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Control of Concrete Cracking in Bridges
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM
NCHRP SYNTHESIS 500

Control of Concrete
Cracking in Bridges
A Synthesis of Highway Practice
Consultant
Henry G. Russell
Henry G. Russell, Inc.
Glenview, Illinois
S ubscriber C ategories
Bridges and Other Structures • Construction • Highways • Materials
Research Sponsored by the American Association of State Highway and Transportation Officials
in Cooperation with the Federal Highway Administration
2017
Copyright National Academy of Sciences. All rights reserved.

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP SYNTHESIS 500
Systematic, well-designed research is the most effective way to Project 20-05, Topic 47-01
solve many problems facing highway administrators and engineers. ISSN 0547-5570
Often, highway problems are of local interest and can best be stud- ISBN 978-0-309-38981-5
ied by highway departments individually or in cooperation with Library of Congress Control No. 2016957897
their state universities and others. However, the accelerating growth © 2017 National Academy of Sciences. All rights reserved.
of highway transportation results in increasingly complex problems
of wide interest to highway authorities. These problems are best
studied through a coordinated program of cooperative research. COPYRIGHT INFORMATION
Recognizing this need, the leadership of the American Associa-
Authors herein are responsible for the authenticity of their materials and
tion of State Highway and Transportation Officials (AASHTO) in for obtaining written permissions from publishers or persons who own the
1962 initiated an objective national highway research program using copyright to any previously published or copyrighted material used herein.
modern scientific techniques—the National Cooperative Highway Cooperative Research Programs (CRP) grants permission to reproduce
Research Program (NCHRP). NCHRP is supported on a continuing material in this publication for classroom and not-for-profit purposes.
basis by funds from participating member states of AASHTO and Permission is given with the understanding that none of the material will
receives the full cooperation and support of the Federal Highway be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FRA, FTA,
Office of the Assistant Secretary for Research and Technology, PHMSA,
Administration, United States Department of Transportation. or TDC endorsement of a particular product, method, or practice. It is
The Transportation Research Board (TRB) of the National Acad- expected that those reproducing the material in this document for
emies of Sciences, Engineering, and Medicine was requested by educational and not-for-profit uses will give appropriate acknowledgment
AASHTO to administer the research program because of TRB’s of the source of any reprinted or reproduced material. For other uses of the
recognized objectivity and understanding of modern research material, request permission from CRP.
practices. TRB is uniquely suited for this purpose for many rea-
sons: TRB maintains an extensive committee structure from which
authorities on any highway transportation subject may be drawn; NOTICE
TRB possesses avenues of communications and cooperation with The report was reviewed by the technical panel and accepted for publication
federal, state, and local governmental agencies, universities, and according to procedures established and overseen by the Transportation
industry; TRB’s relationship to the Academies is an insurance of Research Board and approved by the National Academies of Sciences,
objectivity; and TRB maintains a full-time staff of specialists in Engineering, and Medicine.
The opinions and conclusions expressed or implied in this report are
highway transportation matters to bring the findings of research those of the researchers who performed the research and are not necessari-
directly to those in a position to use them. ly those of the Transportation Research Board; the National Academies of
The program is developed on the basis of research needs identi- Sciences, Engineering, and Medicine; or the program sponsors.
fied by chief administrators and other staff of the highway and trans- The Transportation Research Board; the National Academies of Sciences,
portation departments and by committees of AASHTO. Topics of Engineering, and Medicine; and the sponsors of the National Cooperative
the highest merit are selected by the AASHTO Standing Committee Highway Research Program do not endorse products or manufacturers.
Trade or manufacturers’ names appear herein solely because they are con-
on Research (SCOR), and each year SCOR’s recommendations are
sidered essential to the object of the report.
proposed to the AASHTO Board of Directors and the Academies.
Research projects to address these topics are defined by NCHRP,
and qualified research agencies are selected from submitted propos-
als. Administration and surveillance of research contracts are the
responsibilities of the Academies and TRB.
The needs for highway research are many, and NCHRP can make
significant contributions to solving highway transportation prob-
lems of mutual concern to many responsible groups. The program,
however, is intended to complement, rather than to substitute for or
duplicate, other highway research programs.
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The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non-
governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for
outstanding contributions to research. Dr. Marcia McNutt is president.
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including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested
in the development of transportation.
Learn more about the Transportation Research Board at www.TRB.org.

TOPIC PANEL 47-01

JOHN BELCHER, Michigan Department of Transportation, Lansing
BIJAN KHALEGHI. Washington State Department of Transportation, Tumwater
WILL LINDQUIST, Kansas Department of Transportation, Topeka
WILLIAM POTTER, Florida Department of Transportation, Tallahassee
CARIN L. ROBERTS-WOLLMANN, Virginia Polytechnic Institute and State University, Blacksburg
AMY E. SMITH, HDR, Austin, TX
BENJAMIN A. GREYBEAL, Federal Highway Administration (Liaison)
REGGIE H. HOLT, Federal Highway Administration (Liaison)
SYNTHESIS STUDIES STAFF

STEPHEN R. GODWIN, Director for Studies and Special Programs
JON M. WILLIAMS, Program Director, IDEA and Synthesis Studies
MARIELA GARCIA-COLBERG, Senior Program Officer
JO ALLEN GAUSE, Senior Program Officer
GAIL R. STABA, Senior Program Officer
TANYA M. ZWAHLEN, Consultant
DON TIPPMAN, Senior Editor
CHERYL KEITH, Senior Program Assistant
DEMISHA WILLIAMS, Senior Program Assistant
DEBBIE IRVIN, Program Associate
COOPERATIVE RESEARCH PROGRAMS STAFF

CHRISTOPHER J. HEDGES, Interim Director, Cooperative Research Programs
EILEEN P. DELANEY, Director of Publications
NCHRP COMMITTEE FOR PROJECT 20-05
CHAIR
BRIAN A. BLANCHARD, Florida Department of Transportation
MEMBERS
STUART D. ANDERSON, Texas A&M University
SOCORRO “COCO” BRISENO, California Department of Transportation
DAVID M. JARED, Georgia Department of Transportation
CYNTHIA L. JONES, Ohio Department of Transportation
MALCOLM T. KERLEY, NXL, Richmond, Virginia
JOHN M. MASON, JR., Auburn University
CATHERINE NELSON, Salem, Oregon
ROGER C. OLSON, Minnesota Department of Transportation (Ret.)
BENJAMIN ORSBON, South Dakota Department of Transportation
RANDY PARK, Utah Department of Transportation
ROBERT L. SACK, New York State Department of Transportation
FRANCINE SHAW WHITSON, Federal Highway Administration
JOYCE N. TAYLOR, Maine Department of Transportation
FHWA LIAISON
JACK JERNIGAN
TRB LIAISON
STEPHEN F. MAHER
Cover figure: End zone cracks in a prestressed concrete beam (Courtesy: University of Wisconsin and Concrete Bridge Views
published jointly by FHWA and the National Concrete Bridge Council).

FOREWORD Highway administrators, engineers, and researchers often face problems for which infor-
mation already exists, either in documented form or as undocumented experience and prac-
tice. This information may be fragmented, scattered, and unevaluated. As a consequence,
full knowledge of what has been learned about a problem may not be brought to bear on its
solution. Costly research findings may go unused, valuable experience may be overlooked,
and due consideration may not be given to recommended practices for solving or alleviat-
ing the problem.
There is information on nearly every subject of concern to highway administrators and
engineers. Much of it derives from research or from the work of practitioners faced with
problems in their day-to-day work. To provide a systematic means for assembling and
evaluating such useful information and to make it available to the entire highway commu-
nity, the American Association of State Highway and Transportation Officials—through
the mechanism of the National Cooperative Highway Research Program—authorized the
Transportation Research Board to undertake a continuing study. This study, NCHRP Proj-
ect 20-5, “Synthesis of Information Related to Highway Problems,” searches out and syn-
thesizes useful knowledge from all available sources and prepares concise, documented
reports on specific topics. Reports from this endeavor constitute an NCHRP report series,
Synthesis of Highway Practice.
This synthesis series reports on current knowledge and practice, in a compact format,
without the detailed directions usually found in handbooks or design manuals. Each report
in the series provides a compendium of the best knowledge available on those measures
found to be the most successful in resolving specific problems.
PREFACE Cracking of concrete in bridges continues to be a concern for bridge owners, particularly
By Jon M. Williams with bridge decks exposed to severe environments. The control of cracking for aesthetic,
Program Director durability, and structural reasons becomes increasingly important as service-life goals
Transportation are extended and higher-strength concrete, higher-strength reinforcement, and different
Research Board types of reinforcement are used in bridge construction. This study provides information
on methods used to control concrete cracking in bridge superstructures and substructures,
and on the influence of cracking on long-term durability.
The study found that no single best practice can be used to enhance concrete bridge
deck performance. Useful practices include reducing drying shrinkage of the concrete mix;
reducing temperature differences; nighttime concrete placements; and the use of supple-
mentary cementitious materials, internal curing, shrinkage-reducing admixtures, or shrinkage-
compensating concrete. Wet curing of concrete decks beginning immediately after concrete
finishing and continuing for at least 7 days, followed by the application of a curing com-
pound, was identified as an appropriate construction practice for concrete bridge decks.
For prestressed concrete beams, end zone cracking can often be prevented by revising the
detensioning sequence. Cracking in concrete substructures was of less concern than in super
structure components.
Henry G. Russell, Henry G. Russell, Inc., Glenview, Illinois, collected and synthesized
the information and wrote the report. The members of the topic panel are acknowledged
on the preceding page. This synthesis is an immediately useful document that records the
practices that were acceptable within the limitations of the knowledge available at the time
of its preparation. As progress in research and practice continues, new knowledge will be
added to that now at hand.

INTRODUCTION
In 1969, the U.S.DOT was two years old, the Boeing 747 made its first flight, and Apollo 11 landed
on the moon. The Woodstock music festival was held in upstate New York, Wal-Mart was founded,
and the “Miracle Mets” won the World Series.
At the Highway Research Board (now TRB), the NCHRP had been in existence for just seven
years. In the late ’60s, something had become clear to the staff and sponsors: not every problem
faced by transportation practitioners required new research. Many state and local agencies developed
their own solutions to day-to-day problems and issues, but had no idea what practices were being
employed by their colleagues across the country, or how effective they were. As it was phrased at
the time, “There exists a vast storehouse of information relating to nearly every subject of concern to
highway administrations and engineers. Much of it results from research and much from successful
application of the engineering ideas of men faced with problems in their day to day work.” Setting
aside the quaint notion that in 1969 apparently only men had engineering ideas, the idea was born for
a new program to seek out, compile, and synthesize the most useful knowledge and current practices
for the benefit of transportation practitioners.
NCHRP Synthesis No. 1 dealt with a topic that is still of vital importance today: the safety of
road maintenance workers. The report Traffic Control for Freeway Maintenance documented how
agencies supplemented the Manual on Uniform Traffic Control Devices with standard worksite
layouts and detailed instructions on their placement and removal. The Synthesis outlined how some
agencies provided additional signing and lighting to accommodate night work, including “electric
lights placed under translucent plastic traffic cones.”
Four hundred and ninety-nine (499) studies later, the Synthesis of Practice is consistently the
highest rated annual project by NCHRP’s governing board, the AASHTO Standing Committee
on Research and its Research Advisory Committee. The time and money saved by identifying and
employing practices documented in the Synthesis series have saved countless dollars, time, and lives.
Incidentally, the first syntheses included a postage-paid postcard that could be filled out and
returned with responses to two questions: how did readers apply the information in the synthesis,
and how could the synthesis be improved to be more effective? As TRB continues to seek ways to
understand and maximize the impacts of its work, these two questions are as relevant today as they
were in 1969. Don’t expect to see postcards that require a hand-written response, but don’t be sur-
prised to see us asking these two simple questions more often in the future.
Neil Pedersen, Executive Director

Transportation Research Board

CONTENTS
1 SUMMARY
3 CHAPTER ONE INTRODUCTION
Background, 3
Objectives and Scope, 3
Study Approach, 4
Report Organization, 4
5 CHAPTER TWO TYPES AND CAUSES OF CONCRETE CRACKING

IN BRIDGES
Plastic Shrinkage Cracks, 5
Plastic Settlement Cracks, 5
Autogenous Shrinkage, 6
Drying Shrinkage Cracks, 6
Thermal Cracks, 6
Cracking in Bridge Decks, 6
Cracking in Adjacent Box Beam Bridges and Slab Beam Bridges, 19
Cracking in Pretensioned Concrete Beams, 21
Cracking in Nonprestressed Concrete Beams, 25
Cracking in Substructures, 26
Effective Practices for Control of Concrete Cracking, 28
31 CHAPTER THREE EFFECTS OF CONCRETE CONSTITUENT MATERIALS

ON CRACKING
Concrete Constituent Materials for Bridge Decks, 31
Concrete Constituent Materials for Other Components, 36
Internal Curing, 37
Self-Consolidating Concrete, 39
Summary of the Effects of Concrete Constituent Materials, 39
40 CHAPTER FOUR EFFECTS OF CONSTRUCTION PRACTICES ON CRACKING

Curing Practices, 40
Weather Conditions, 42
Placement Length and Construction Sequence, 42
Other Practices, 43
Summary of Construction Practices, 43
44 CHAPTER FIVE EFFECTS OF REINFORCEMENT TYPE ON CRACK CONTROL

Yield Strength of Reinforcement, 44
Corrosion-Resistant Steel Reinforcement, 44
Fiber-Reinforced Polymer Reinforcement, 45
Specifications for Crack Control, 47
Conclusions About the Effects of Reinforcement Type on Crack Control, 53

54 CHAPTER SIX INFLUENCE OF CRACKING ON LONG-TERM

BRIDGE PERFORMANCE
AASHTO LRFD Specifications for Durability, 56
Permissible Crack Widths, 56
Determination of Bar Spacing to Control Crack Widths, 57
Service Life, 59
Conclusions About the Influence of Cracking on Long-Term Bridge Performance, 60
61 CHAPTER SEVEN CASE EXAMPLES

California Department of Transportation, 61
Kansas Department of Transportation, 62
Pennsylvania Department of Transportation, 64
Washington State Department of Transportation, 65
68 CHAPTER EIGHT Conclusions and Suggestions for Future Research

Conclusions, 68
Suggestions for Future Research, 70
72 ABBREVIATIONS
73 REFERENCES
83 APPENDIX A Survey Questionnaire
88 APPENDIX B Summary of Responses to Survey Questionnaire
101 APPENDIX C Cross Reference Table for AASHTO

LRFD Bridge Design Specifications
102 APPENDIX D Research Problem Statement
Note: Photographs, figures, and tables in this report may have been converted from color to
grayscale for printing. The electronic version of the report (posted on the web at www.trb.org)
retains the color versions.

Control Of Concrete Cracking in Bridges
Summary Many advances in bridge design, concrete technology, and reinforcement materials have been made
over the years. Nevertheless, cracking of concrete in bridges continues to be a concern for bridge
owners, particularly in bridge decks exposed to severe environments. The presence of cracks pro-
vides a direct path for water and chlorides to penetrate the concrete and reach the reinforcement,
which can lead to corrosion of steel reinforcement or degradation of the concrete.
The AASHTO LRFD (load and resistance factor design) Bridge Design Specifications provide
requirements for minimum amounts of reinforcement and maximum spacing of reinforcement
to control crack widths. Some requirements are based on in-depth research; others are based on
experience. Nevertheless, bridge owners find the need to supplement the AASHTO specifications
with their own requirements. The control of cracking for aesthetic, durability, and structural reasons
becomes increasingly important as service-life goals are extended and higher strength concrete, higher
strength reinforcement, and different types of reinforcement are used in bridge construction.
The primary objectives of this synthesis are to provide a compilation and discussion of methods
used to control concrete cracking in bridge superstructures and substructures and to present informa-
tion on the influence of cracking on long-term durability. Superstructure components discussed in this
synthesis include full-depth, cast-in-place concrete decks; partial-depth, precast concrete panels with
a cast-in-place topping; full-depth, precast concrete deck panels; and prestressed and nonprestressed
concrete beams. Information for concrete decks on both steel and concrete beams is included. Sub-
structure components include pier caps, columns, abutments, and pile caps.
Information for this synthesis was obtained from a literature review, surveys of state departments
of transportation, and surveys of provincial and territorial agencies in Canada. The survey achieved
a 78% response rate from U.S. agencies (39 responses). Information gathered in this synthesis pro-
vides a basis to understand the causes of concrete cracking in bridges and helps to establish the most
practical and efficient methods for reducing the occurrence of cracking and controlling cracking
when it occurs.
The survey of the state departments of transportation and Canadian agencies provided information
about the frequency of concrete cracking, materials being used in concrete mixes, types of reinforce-
ment being used, and practices that were successful and unsuccessful in reducing bridge deck cracking.
Concrete cracking occurs most often in full-depth, cast-in-place, concrete bridge decks.
The successful practices to reduce bridge deck cracking generally relate to reducing drying shrink-
age of the concrete mix and reducing temperature differences. Drying shrinkage can be reduced by
limiting the amounts of cementitious materials and water in the concrete and using the largest practi-
cal size of aggregate in combination with appropriate construction practices. These practices include
avoiding high compressive strength concrete, applying wet curing immediately after finishing the
concrete surface, continuing wet curing for at least 7 days, and applying a curing compound after
the wet curing to slow moisture loss from the concrete. Temperature differences can be controlled
by limiting the temperature of the concrete at time of placement and ensuring that the concrete tem-
perature does not increase too much as the concrete hydrates. Nighttime concrete placements also
can be beneficial, particularly in hot climates. Overall, no single most effective practice can be used
to enhance concrete bridge deck performance.

2
Practices that show potential for reduction of shrinkage and shrinkage cracking include the use of
supplementary cementitious materials, internal curing, shrinkage-reducing admixtures, or shrinkage-
compensating concrete.
End zone cracking, which occurs in prestressed concrete beams, is an uncommon occurrence and
often can be prevented by revising the detensioning sequence. Cracks that occur can be controlled
through the use of appropriate reinforcement.
Concrete used in substructures also cracks but far less frequently than that used in concrete bridge
decks. Consequently, there appears to be much less concern about substructure cracks. In most cases,
the substructure is protected from rain and deicing salts by the superstructure and thus is not subject
to the same harsh exposure.
Based on the survey results, most U.S. highway agencies use epoxy-coated reinforcement for cor-
rosion resistance. Some states have used zinc-coated, stainless-steel–coated, or solid stainless steel
reinforcement. They reported that the use of these materials had no noticeable effect on deck crack-
ing. However, the use of fiber-reinforced polymer reinforcement has a major effect on crack widths
because the reinforcement has a lower stiffness. Consequently, the amount of fiber-reinforced polymer
reinforcement often is determined on the basis of controlling crack widths rather than satisfying the
need for structural strength.
Four case examples are included describing the steps taken by the states of California, Kansas,
Pennsylvania, and Washington to reduce the severity of cracking in their bridge decks.
The response to the survey resulted in eight topics suggested for research. A research problem
statement incorporating several of the topics related to the use of reinforcement to control cracking
was developed.

3
chapter one
Introduction
Background
Despite many advances in bridge design, concrete technology, and corrosion-resistant reinforce-
ment, cracking of concrete members continues to be a concern for bridge owners, particularly for
bridges exposed to severe environments. The presence of cracks provides a direct path for water and
chlorides to penetrate concrete and reach the reinforcement, a process that can lead to degradation of
the concrete or corrosion of steel reinforcement.
The AASHTO LRFD (load and resistance factor design) Bridge Design Specifications (AASHTO
2017) provide requirements for minimum amounts of reinforcement and maximum spacing of
reinforcement to control crack widths. Some requirements are based on in-depth research; others are
based on experience. Nevertheless, bridge owners find the need to supplement the AASHTO specifi-
cations with their own requirements. The control of cracking for aesthetic, durability, and structural
reasons becomes increasingly important as service-life goals are extended and higher strength concrete,
higher strength reinforcement, and different types of reinforcement are used in bridge construction.
A need existed to compile the latest information about the state of the practice for control of
concrete cracking in bridges and to identify the significance of cracking on long-term durability.
Objectives and Scope
The objectives of this synthesis are to
• Provide a compilation and discussion of methods used to control concrete cracking in bridge
superstructures and substructures, and
• Present information on the influence of cracking on long-term durability.
The scope includes information about the effect of the following on control of cracking:
• Concrete mix design and performance requirements,

• Construction practices,
• Structural design requirements,
• Steel reinforcement with yield strengths from 60 to 100 ksi,
• Corrosion-resistant steel reinforcement, and
• Fiber-reinforced polymer reinforcement.
The discussion includes background study and experience in practice, as well as proven inno-
vative methods. The relationship between environmental exposure conditions and crack-related
parameters, such as width, depth, spacing on concrete degradation, corrosion, and service life, is
addressed. Both lightweight and normal-weight concrete and concrete decks on steel and concrete
beams are discussed.
The scope of this synthesis does not include segmental box girder bridges and cracking caused
by corrosion of reinforcement; detrimental concrete chemical reactions, such as alkali-aggregate
reactivity; or adverse concrete performance from environmental exposure conditions, such as freeze-
thaw damage.

4
Study Approach
Information for this synthesis was obtained from a literature review, surveys of state departments of
transportation (DOTs), surveys of provincial and territorial agencies in Canada, and input from selected
individuals who have in-depth information. The literature search provided many references related to
concrete cracking and concrete shrinkage; such references were too numerous to all be included in this
synthesis. Consequently, the synthesis concentrates on publications from 1990 onward, those related
to bridges, and those that provide practical recommendations. Information on international practice,
except for that of Canada, is not included. In addition, many laboratory research projects on shrinkage
and concrete cracking have been performed but are not referenced in this synthesis.
Information gathered in this synthesis provides a basis for understanding the causes of concrete crack-
ing in bridges and helps to establish the most practical and efficient methods for reducing the occurrence
of cracking and controlling cracking when it occurs.
Report Organization
The text of the synthesis is organized as follows:
• Chapter two provides an overview of the different types and causes of concrete cracking that
can occur in concrete and steel bridges. The crack types are those associated with flexure, tor-
sion, shear, splitting, plastic shrinkage, plastic settlement, autogenous shrinkage, drying shrink-
age, and temperature changes.
• Chapter three provides information about approaches to reduce the potential for cracking through
the selection of concrete constituent materials and use of internal curing.
• Chapter four provides information about the effects of construction practices on cracking, includ-
ing curing, weather conditions, and construction sequence.
• Chapter five includes information about the effects of different types of reinforcement on crack-
ing. It discusses the effects of using steel reinforcement with specified yield strengths from 60
to 100 ksi, corrosion-resistant steel reinforcement, and fiber-reinforced polymer (FRP) rein-
forcement. Specifications for reinforcement to control cracking and practices to supplement the
specifications are described.
• Chapter six discusses the influence of cracking on long-term durability, including permissible
crack widths, bar spacing, and service life.
• Chapter seven provides four case examples showing how the states of California, Kansas,
Pennsylvania, and Washington have reduced the severity of cracking in their concrete bridge
decks.
• Chapter eight provides a summary of the key findings of the synthesis project, including the state
of the practice for control of cracking in bridges and “effective practices.” Key findings and con-
clusions are summarized. Suggestions for future research are offered.
• Appendices provide the survey questionnaire (Appendix A), a compilation of the responses to the
questionnaire (Appendix B), a cross reference table between the article numbers used in the sev-
enth and eighth editions of the AASHTO LRFD Bridge Design Specifications for those articles
referenced in this synthesis (Appendix C), and a research problem statement (Appendix D).
The eighth edition of the AASHTO LRFD Bridge Design Specifications contains a reorganized
version of the seventh edition’s Section 5: Concrete Structures. Because of the reorganization, many
articles have been renumbered. Article numbers used in this synthesis are based on the eighth edition,
with the corresponding number for the seventh edition included in parentheses.

5
chapter two
Types and Causes of Concrete Cracking

in Bridges
Cracks in reinforced concrete members can be classified into two main categories (Leonhardt 1977):
• Cracks caused by externally applied loads, and

• Cracks that occur independent of the loading conditions.
Cracks caused by external loads are generally flexural and shear cracks and occur after the con-
crete has hardened. Cracks independent of the loading condition include plastic shrinkage cracks,
settlement cracks, drying shrinkage cracks, thermal cracks, and map or pattern cracks. Cracks may
also be described by their orientation, such as longitudinal, transverse, diagonal, or random (Patnaik
and Baah 2015).
In the survey for this synthesis, agencies were asked what lessons they have learned about con-
trolling concrete cracking. Several agencies mentioned the necessity of timely and proper water or
moist curing. Several agencies also mentioned that drying shrinkage was a major source of cracking,
and that modifications to the concrete constituent materials to reduce shrinkage are beneficial. Modi-
fications that were mentioned included the use of a shrinkage-reducing admixture (SRA), includ-
ing fibers in the concrete mix, limiting cement or paste content, and internal curing. However, one
agency stated that “nothing will eliminate cracking in concrete.”
Plastic Shrinkage Cracks
Plastic shrinkage occurs near the surface of freshly placed concrete when moisture evaporates from
the surface faster than it is replaced by bleed water [American Concrete Institute (ACI) Commit-
tee 224 2007]. Plastic shrinkage cracking is more likely to occur under conditions that produce high
evaporation rates, such as high air and concrete temperatures, low humidity, and high wind velocity
over the concrete surface. In addition, concrete mixes with lower amounts of bleed water, such as those
containing supplementary cementitious materials (SCMs), have a greater tendency to exhibit plastic
shrinkage cracks (ACI Committee 224 2008). In bridges, plastic shrinkage cracks are most likely to
occur in the decks because of the relatively large surface area compared with the thickness.
Plastic shrinkage cracks can be unsightly but do not normally affect the structural performance of
the concrete member. In most cases, the cracks do not penetrate the full depth of the member but may
act as initiators for full-depth cracks (TRB 2006). Plastic shrinkage can be minimized through the
use of fibers (Kosmatka and Wilson 2016). The most effective solution is to prevent such cracks from
occurring by providing a saturated atmosphere over all exposed surfaces during the curing process.
Thus, it is important to cover the top surface of the concrete with a moisture-proof cover as soon as
concrete placement and finishing are complete.
Plastic Settlement Cracks
Plastic settlement cracks occur when concrete continues to consolidate under its own weight after
initial placement, vibration, and finishing. The cracks are most likely to occur when the vertical
settlement is restrained by horizontal reinforcing bars. Settlement cracking increases with larger bar
sizes, higher concrete slump, and smaller concrete cover (Dakhil et al. 1975; Weyers et al. 1982;
Babaie and Fouladgar 1997).

6
The likelihood of settlement cracking can be reduced by proper vibration of the concrete, use
of the lowest possible slump, and increasing the concrete cover in conventional concrete or using
viscosity-modifying admixtures in self-consolidating concrete (SCC). Plastic settlement cracks can
be reduced through the use of fibers (Kosmatka and Wilson 2016). As with plastic shrinkage cracks,
it is best to prevent plastic settlement cracks by using proper construction procedures.
Autogenous Shrinkage
Autogenous shrinkage is a reduction in volume caused by the chemical process of hydration of cement.
It is most prominent in concretes with water/cementitious materials (w/cm) ratios of less than about
0.40. Consequently, high-strength concretes may have large amounts of autogenous shrinkage. Autog-
enous shrinkage can contribute to plastic shrinkage cracking (TRB 2006). Concretes susceptible to
large amounts of autogenous shrinkage should be cured with external water for at least 7 days to
minimize crack development (Kosmatka and Wilson 2016).
Drying Shrinkage Cracks
Drying shrinkage is caused by the loss of moisture from the cement paste in the concrete. When the
drying shrinkage is restrained by other components, tensile stresses develop in the shrinking concrete
and can lead to cracking. Such is the case for concrete decks cast on steel or concrete beams. The mag-
nitude of the tensile stress is influenced by many factors, including the amount and rate of shrinkage,
the degree of restraint, the modulus of elasticity, and the amount of creep (ACI Committee 224 2007).
The amount of shrinkage is influenced by the concrete constituent materials and the member size. Thin-
ner members have more shrinkage and shrink at a faster rate than do thicker members.
Thermal Cracks
Temperature differences between different components in a concrete structure are caused by dif-
ferent heats of hydration, different cooling rates, and ambient temperature changes. For example, a
bridge deck will heat more quickly from sunshine than will the girders supporting the deck. When
these temperature differences occur, tensile stresses result, which can lead to thermal cracks. Ther-
mal cracks can also occur when the two components have the same temperature change but have
different coefficients of thermal expansion.
This rest of this chapter addresses the causes and types of cracking in hardened concrete for each
of the major components of a bridge.
Cracking In Bridge Decks
Cracks in concrete bridge decks are generally characterized by their orientation with respect to the
longitudinal axis of the bridge (ACI Committee 345 2011). The major types are transverse, longitu-
dinal, diagonal, and random. Transverse cracks are illustrated in Figure 1. In addition, there is map
cracking, which is also called pattern cracking or crazing. In hardened concrete, cracks form where the
tensile stress in the concrete exceeds the tensile strength of the concrete. Tensile stresses are caused by
applied loads such as vehicles or restraint to the length changes caused by shrinkage or temperature
changes. The tensile strength of the concrete depends on the concrete constituent materials, curing
environment, and concrete age.
Some cracking in nonprestressed concrete bridge decks is inevitable because the cross section is
expected to crack before the reinforcement becomes effective. Such cracks include the following:
• Transverse cracks over intermediate supports caused by negative moments from dead and
live loads;
• Diagonal cracks caused by torsional forces in the acute corners of skew bridges, as illustrated
in Figure 2;

7
FIGURE 1 Transverse cracking in a bridge deck (Courtesy:

Michigan Department of Transportation).
• Cracking in curved bridges caused by torsional forces;

• Longitudinal cracks at the ends of spans, particularly where the bridge deck is integral with the
abutment; and
• Cracks at construction joints.
Because some cracks are inevitable, their width and spacing need to be controlled through the use of
reinforcement. This is discussed in chapter five.
The incidence of cracking increases with span length [Larson et al. 1968; Axon et al. 1969; Portland
Cement Association (PCA) 1970], angle of skew (Larson et al. 1968), and use of continuous structures
(Axon et al. 1969; PCA 1970).
Full-Depth, Cast-in-Place Concrete Decks
Cracking in concrete bridge decks is not a new phenomenon. In 1961, the PCA began a study of
concrete bridge deck durability (PCA 1970). The study included a survey of 1,000 bridges selected
FIGURE 2 Diagonal cracking in an acute corner of a skewed bridge

(Courtesy: Henry G. Russell, Inc.).

8
at random in eight states and a detailed survey of 70 bridges in four states. The study concluded that
transverse cracking was the dominant type of cracking. These cracks typically were located above
transverse reinforcing bars. Several other studies have identified that longitudinal and transverse
cracks tend to fall directly above reinforcing bars in the top layer of reinforcement because the pres-
ence of the reinforcement acts as a stress raiser, but this is not always the case (Cheng and Johnston
1985; Perfetti et al. 1985; Kochanski et al. 1990). The formation of these cracks can be initiated by
the presence of plastic shrinkage cracks. A 1996 survey indicated that more than 100,000 bridge
decks in the United States have experienced early-age transverse cracking (Brown et al. 2007).
In the survey for this synthesis, agencies were asked which types of concrete cracking their bridges
had experienced in the past 5 years in cast-in-place (CIP) concrete decks with removable formwork
or stay-in-place steel forms on both steel and concrete beams. The results are summarized in Figure 3.
On the positive side, nearly one quarter of the agencies reported that cracks occurred infrequently.
On the negative side, more than one-half of the agencies reported that cracks occurred frequently.
Fewer agencies reported frequent cracking when stay-in-place metal formwork was used compared
with removable formwork. This could be the result of fewer states using stay-in-place formwork.
The agencies were asked to identify the strategies they are using to minimize cracking in CIP con-
crete bridge decks. Their responses are provided in Table 1 along with the results of surveys in 2012
(Russell 2013) and 2003 (Russell 2004).
Based on this table, the strategies used by at least 85% of the agencies are to specify minimum
concrete compressive strength, minimum concrete temperature at placement, maximum concrete tem-
perature at placement, maximum w/cm ratio, maximum slump, and a minimum wet curing period.
These strategies are the same as those that were rated highly in a 2012 survey (Russell 2013), as shown
in Table 1. One difference between the 2012 and 2016 surveys is that more agencies now specify a
maximum concrete temperature during curing.
Agencies were asked to identify the strategies that were most or least effective in minimizing
cracking in full-depth, CIP concrete decks. Although 23 strategies were listed as most effective, the
strategy cited most often was to apply wet curing early and provide a minimum wet curing period
for the deck, followed by the application of a curing compound. The strategy cited second most often
was the use of fogging to reduce evaporation rates during concrete placement. The third most often
FIGURE 3 Frequency of cracking in full-depth, CIP concrete bridge decks.

9
Table 1
Strategies to Minimize Cracking in CIP Bridge Decks
2012 2003
2016 Survey
Survey Survey
Strategy to Minimize Bridge Deck Cracking No. % % %
None 2 10 – –
Specify minimum cementitious materials content 23 59 76 –
Specify maximum cementitious materials content 20 51 54 33
Specify minimum concrete compressive strength 34 90 94 –
Specify maximum concrete compressive strength 4 10 13 4
Specify a ratio between 7- and 28-day compressive strengths 3 8 16 –
Specify minimum concrete temperature at placement 34 85 83 –
Specify maximum concrete temperature at placement 37 90 94 80
Specify maximum concrete temperature during curing 23 61 30 –
Specify maximum water-cementitious materials ratio 39 95 94 –
Specify maximum slump 36 88 86 98
Specify maximum water content 20 53 42 –
Specify the use of a shrinkage-reducing admixture 9 23 – –
Specify the use of a shrinkage-compensating concrete 6 16 – –
Specify the use of fibers 10 25 – –
Require use of the ACI surface evaporation nomogram 25 63 55 –
Require wind breaks during concrete placement 15 39 38 22
Require evaporation retardants 13 33 28 29
Specify internal curing 4 11 – –
Require fogging during placement when evaporation rates are high 27 68 77 67
Specify a minimum wet curing period 40 95 100 –
Other 11 48 54 –
– = Strategy was not listed in the survey.
cited strategy was a reduction in the cement and paste content. The full list of strategies is provided
in the answer to Question 7 in Appendix B.
Fifteen strategies were identified as least effective in minimizing cracking in full-depth CIP concrete
bridge decks. The strategy listed most often as least effective related to not requiring or enforcing the
use of wet curing per the specifications. The strategies cited next most often were the use of fogging
and the use of fibers. The full list of strategies is provided in the answer to Question 8 in Appendix B.
In a 2012 survey for NCHRP Synthesis 441: High Performance Concrete Specifications and Prac-
tices for Bridges (Russell 2013), state highway agencies identified that drying shrinkage cracking
was a dominant issue in using high-performance concrete (HPC) in CIP bridge decks. It appeared
that the use of HPC had not eliminated the concerns about deck cracking, although the use of HPC
resulted in better performance overall.
Individual agencies also reported that use of the following contributed to increased deck cracking:
• High early strength concrete;

• High-strength concrete;
• Silica fume;
• Larger cement content to produce lower permeability;
• Fly ash; and
• Evaporation retardant.
One agency reported in 2012 that the use of an SRA had helped reduce cracking but not to a satis-
factory degree. The responses did not show any consensus. The one practice that was not successful
in three states was the use of silica fume.
As a means of limiting the free shrinkage of concrete, the criteria listed in Table 2 have been used.
Based on the numbers in Table 2, a reasonable criterion would be less than 300 to 350 millionths
after 28 days of drying. Most of these criteria are based on tests using AASHTO T 160: Length

10
Table 2
Shrinkage Requirements
Shrinkage Length of
(millionths) Drying Application Reference
300a 28 days Caltrans specifications Maggenti et al. (2013)
450 180 days Caltrans specifications Maggenti et al. (2013)
350 56 days Angeles Crest Bridge, Calif. Higareda (2010)
360 21 days SEAOC Class M Higareda (2010)
600 32 weeks Route 36 Highlands Bridge, N.J. Kolota (2011)
320 28 days WSDOT Gaines and Sheikhizadeh (2013)
700 4 months Bridge decks Purvis et al. (1995)
500 180 days Benicia-Martinez Bridge, Calif. Murugesh and Cormier (2007)
450 180 days San Francisco Oakland Bay Bridge, Calif. Brown (2007)
350 28 days Virginia DOT Nair et al. (2016b)
450 28 days Oregon DOT research Ideker et al. (2013)
a
Later changed to 320 millionths (0.032%).
Change of Hardened Hydraulic Cement Mortar and Concrete, but the initial curing period may be
different. A low shrinkage alone does not guarantee that cracking will not occur. However, it does
reduce the likelihood of cracking.
In Kansas, 59 bridge decks were investigated to identify factors that contribute to cracking (Schmitt
and Darwin 1995, 1999; Miller and Darwin 2000; Lindquist et al. 2005). The investigations concluded
that concrete shrinkage or restraint of concrete shrinkage was a major contributor to bridge deck
cracking. Additional details of the Kansas activities are provided in chapter seven.
In 1994, New York State developed an HPC designated as Class HP (Streeter 1999). One of the
goals of Class HP was to reduce cracking. The newly developed concrete was achieved by using fly
ash and silica fume to reduce the cement content, lowering the w/cm ratio, and using normal range
water-reducing admixtures. Streeter (1999) reported that cracking in the HPC bridge decks resulted
for a variety of reasons. If there was not sufficient retardation during placement, cracks developed,
primarily on multispan continuous structures. Shrinkage cracks occurred when curing was delayed
or fresh concrete was placed on existing concrete that was not in a saturated, surface dry condition.
This latter problem was prevented by placing soaker hoses or sprinklers on the existing concrete for
12 or more hours below concrete placement.
To quantify the effects of the use of Class HP concrete, 84 bridge decks, built from 1995 to 1998,
were inspected (Owens and Alampalli 1999). Deck ages ranged from 1 to 4 years. The results of the
study showed that 49% of the inspected decks exhibited no cracking. Transverse cracking was found
on 48% of the decks and longitudinal cracking on 44%. Forty percent of the bridge decks exhibited
both transverse and longitudinal cracking. It was observed that most cracks occurred within 2 weeks
of the deck placement. Visual inspections revealed that the HPC decks cracked with less frequency
and exhibited narrower and shorter cracks than did their non–high-performance counterparts.
Krauss and Rogalla (1996) monitored the temperatures and strains in the replacement deck of
the Portland–Columbia Bridge between Pennsylvania and New Jersey. During the first 12 hours, the
temperature of the deck climbed from 80°F to as high as 131°F from the heat of hydration. After
48 hours, the temperature rise had dissipated. The authors concluded that the differential temperature
alone was not sufficient to cause deck cracking. However, significant cracking occurred after 18 to
41 days of air drying.
A survey of 72 bridges for transverse deck cracking in the Minneapolis-St. Paul metropolitan area
was reported by French et al. (1999). The survey included 34 simply supported, prestressed concrete
girder bridges; 34 continuous, steel girder bridges; and four continuous, rolled steel wide-flange
girder bridges. Overall, the decks of bridges with simply supported prestressed concrete girders were
observed to be in better condition than decks on continuous steel girder bridges. This was attributed
to reduced end restraint and the beneficial creep and shrinkage characteristics of the prestressed con-
crete girders. The few prestressed concrete girder bridge decks that consistently performed poorly

11
were either bridges with reconstructed or re-overlaid decks, or bridges that had decks placed during
extreme temperature conditions. Cracking as a result of deck reconstruction was attributed to shrink-
age of the deck being restrained by the aged prestressed concrete girders.
For the steel girder bridges, end restraint and shrinkage were the most significant factors contrib-
uting to deck cracking. The steel girder bridges had more cracking on interior spans than end spans,
more cracking in curved bridges compared with straight bridges, more cracking with No. 6 bars than
No. 5 bars as transverse reinforcement, and more cracking with increased restraint owing to steel
configuration, girder depth, and closer girder spacing.
A November 2002 multistate survey for the Michigan DOT showed that 30 (97%) of the 31 respond-
ing states had detected early-age cracking in reinforced concrete bridge decks, and 25 (81%) of the
states reported that the cracking was observed in the first few months (Aktan et al. 2003). Almost all
states reported that transverse cracking was most prevalent.
The Michigan research (Aktan et al. 2003) established the mechanism by which the cracks formed
as thermal stresses that develop during the cement hydration process and, in most cases, during the
first 12 to 24 hours after concrete placement. A temperature difference of approximately 20°F was
established as sufficient to initiate cracking. An increase in drying shrinkage arising from delays in
both concrete placement and application of wet curing also affected deck cracking.
Based on a survey of 36 state transportation agencies, Fu et al. (2007) reported that most diagonal
corner cracks in skewed bridges were observed in the first 3 months after bridge construction. The cracks
generally occurred in the acute corners in a circumferential direction around the corner of the bridge, as
illustrated in Figure 2. After inspection of 40 bridge decks in Michigan, instrumentation of two bridge
decks, and finite element analysis, Fu et al. (2007) concluded that the main cause of corner cracking in
skewed bridges was the temperature rise in the deck caused by the heat of hydration. Measured tempera-
tures in two bridge decks had maximum values of approximately 30°F above the initial temperature of
the concrete. Fu et al. recommended that additional reinforcement be used in the corner areas.
The presence of cracks in newly constructed concrete bridge decks prompted the Colorado DOT
to initiate a study and subsequently to introduce a Class H concrete for exposed bridge decks (Xi et al.
2003). The new concrete required a Type II cement, fly ash, and silica fume for a total cementitious
materials content of between 518 lb/ft3 and 640 lb/ft3, air content between 5% and 8%, and a w/cm
ratio between 0.38 and 0.42. In addition, the concrete had to not exhibit a crack at or before 14 days
when tested in accordance with AASHTO PP 34 (now AASHTO T 334 2012): Standard Method of
Test for Estimating the Cracking Tendency of Concrete.
A subsequent article (Pott and Elkaissi 2009) reported that the Class H mixes had achieved the
objective of less cracking, but at a cost. The capability of testing per AASHTO PP 34 was available
at only two facilities in the state. This presented a challenge for the first two projects. The addition
of new capabilities at other testing facilities reduced this challenge.
Pott and Elkaissi (2009) also reported that completely crack-free bridge decks, curbs, and side-
walks are difficult to obtain because of the restraint of drying shrinkage. Even with the elimination
of negative moment cracking at the piers through alternative structural designs, shrinkage cracking
still created challenges. HPC can mitigate this cracking but is only one component in making the
deck system last 75 to 100 years. Secondary protection systems, such as corrosion protection of the
reinforcement and bridge deck waterproofing systems, also are important components.
Mokarem et al. (2009) reported on the inspection of 19 bridges in 14 states in which the concrete
deck was constructed with HPC. The bridges had been in service for 5 to 10 years and were located
in different climatic regions. A detailed crack survey of each bridge deck was made to document the
number, length, and width of the transverse, diagonal, and longitudinal cracks.
Using the crack survey data from each bridge, the lengths of the transverse, diagonal, and longi-
tudinal cracks on each deck were calculated. The average crack lengths for all the bridge decks were

12
0.073 ft/ft2 transversely; 0.008 ft/ft2 diagonally; and 0.042 ft/ft2 longitudinally, indicating that most
cracks were in the transverse direction. The results also indicated that, in some cases, the use of HPC
reduced bridge deck cracking, whereas in other cases the crack lengths were greater.
When the structural system of the bridge included skewed supports, diagonal cracks developed
near the supports. When the structural system included continuity over the supports, transverse
cracks developed in the negative moment regions.
The 14 bridges that used precast, prestressed concrete beams with a full-depth CIP concrete deck
exhibited a wide range of total crack densities. The bridges in Georgia, Louisiana, New Hampshire
(Route 104), and Tennessee (Hickman) had relatively low total crack densities. In contrast, the bridges
in Alabama, Nebraska, New Mexico, North Carolina, South Dakota, Tennessee (Porter), Virginia, and
Washington had at least twice as much cracking. On average, the latter group of bridges had about
eight times as much cracking as the former group.
For most bridges, the highest crack density occurred for cracks running in the transverse direction.
The exceptions were two bridges in Virginia, which are discussed later. The cracking densities in each
span of each bridge were compared with span lengths, beam spacings, deck thickness, girder types,
clear deck spans, and beam span-to-depth ratios in an attempt to identify any overall correlations.
None were identified. However, some comparisons between crack densities on spans of individual
bridges were relevant.
The Georgia bridge comprises four simply supported spans. The bridge exhibited different patterns
of deck cracking in different spans. The eastbound span 3 and westbound span 2 showed little crack-
ing compared with westbound span 3 and eastbound span 2. Some diagonal cracking perpendicular to
the skewed diaphragms at the end of the spans was present.
The Charenton Canal Bridge in Louisiana has five continuous spans with an average length of
73 ft. Each span consists of five Type III AASHTO girders evenly spaced at 10-ft centers. The CIP
concrete deck is 8 in. thick. A visual inspection of the bridge 228 days after casting did not reveal any
cracks (Bruce et al. 2001). A second visual inspection of the bridge deck, performed about 4 years
after the bridge opened to traffic (Mokarem et al. 2009), revealed some cracks.
Most of the cracks were located in the negative moment regions over the intermediate piers. A total
of 46 transverse cracks were recorded on the bridge with a combined total crack length of 187.4 ft over
a bridge deck area of 16,060 ft2. However, all were hairline cracks with a width less than 0.016 in.
No diagonal or longitudinal cracks were observed. The authors reported that the structural system
of the Charenton Canal Bridge is flexible compared with conventional bridges because of the wider
beam spacing and longer span length. This relatively flexible structural system might have contributed
to the development and widening of some cracks.
The Route 104 bridge over the Newfound River in Bristol, New Hampshire, is a single simple-span
bridge that was completed in 1996 (Waszczuk and Juliano 1999). The superstructure consists of a 9-in.-
thick CIP concrete deck supported on five precast, prestressed concrete girders spaced at 12.5 ft on
center. Until 2000, only some hairline longitudinal flexural cracks over the girder lines were observed;
no transverse or shrinkage cracks were found. A visual inspection of the bridge deck was performed
in 2004 (Mokarem et al. 2009). Only two longitudinal cracks were recorded on the bridge with a com-
bined total crack length of 10 ft over a bridge deck area of 3,218 ft2. The maximum crack width was
0.02 in. No transverse or diagonal cracks were observed.
The concrete utilized 660 lb/yd3 of cementitious material, including 8% silica fume. The w/cm ratio
was 0.39. The concrete compressive strength at 28 days ranged from 8.16 to 9.61 ksi. The modulus of
elasticity ranged from 4,200 to 4,300 ksi. The authors commented that the modulus of elasticity was
lower than expected.
In Tennessee, two similar bridges were inspected. Both bridges were constructed in 2000 and consist
of a two-span continuous structure with span lengths ranging from 139 to 159 ft. The superstructures

13
consist of 8¼-in.-thick concrete decks with stay-in-place forms on four precast concrete bulb-tee gird-
ers at 8 ft 4 in. centers. The bridges have skew angles of 27 and 17.5 degrees. The Porter Road Bridge
deck was cast in January 2000 when the ambient temperature at time of placement was 35°F to 40°F.
Heaters were used on the Porter Road Bridge. The Hickman Road Bridge was cast in May 2000 when
the ambient temperature at time of placement was 70°F.
Both bridges had transverse and diagonal cracks and no longitudinal cracks. However, the total
length of cracks on the Porter Road Bridge was 860 ft compared with 110 ft on the Hickman Road
Bridge. These crack lengths corresponded to crack densities of 0.085 and 0.013 ft/ft2. Most of the
cracks were transverse and on a line along the middle of the deck. Some diagonal cracks were present
at the skewed abutments. The authors speculate that the larger number of cracks on the Porter Road
Bridge was the result of differential temperatures between the heated deck and the cooler beams.
Each of the two bridges in North Carolina consists of two pairs of continuous spans. Most of the
cracking was in the transverse direction and occurred in the half of each span adjacent to the continuity
connection over the pier.
Two bridges in South Dakota were three-span continuous structures with a similar amount of
cracking. Most of the cracking was in the transverse direction with some diagonal cracking at the
skewed abutments.
Two bridges in Virginia had simple spans and were the only two bridges with a full-depth CIP
concrete deck on precast, prestressed concrete beams that had more longitudinal cracking than trans-
verse cracking. The reason for this was unclear in that the structural system for these bridges is
similar to that of the other 12 bridges with full-depth, CIP concrete decks.
Patnaik and Baah (2015) studied the negative moment cracking behavior of 13 reinforced concrete
continuous span slab bridges in Ohio and reported cracks as wide as 0.14 in. under dead load alone.
The measured crack widths were reported to be more than 15 times the maximum limit of 0.007 in.
recommended in ACI 224R-01 for bridge decks exposed to deicing salts (ACI Committee 224 2008).
Based on an investigation into the early-age cracking of concrete bridge decks in California,
Araiza et al. (2011) recommended the following changes to their specifications:
• Replace the minimum cement content of 675 lb/yd3 with a maximum cement content of
600 lb/yd3.
• Specify a maximum paste content of 27% by volume.
• Specify a minimum compressive strength of 3.5 ksi at 28 days unless otherwise required for
structural design.
• Consider a maximum compressive strength of 4.5 ksi at 7 or 14 days.
• Reduce the maximum shrinkage from 0.045% to 0.035% at 28 days.
• Specify an air content of 6% to 8% irrespective of exposure content.
• Avoid the use of silica fume.
• Wet cure the deck for 14 days.
• Apply a white curing membrane after the wet curing period.
• Hold a pre-job conference with the contractor to discuss curing and cracking.
Stringer and Burgueno (2012) inspected 16 bridge decks in Michigan. Transverse cracking was
present in bridge decks supported on concrete beams or steel beams. Longitudinal cracking was present
only in the decks on concrete beams. Cracking was more prevalent in the negative moment regions. The
authors identified that the cause of deck cracking in jointless bridges was restrained concrete shrinkage
caused by the end restraint conditions. They concluded that restrained shrinkage cracking in concrete
decks of jointless bridges is unavoidable in steel and concrete beam bridges. The lowest amount of
cracking was predicted for bridges with nonintegral abutments or low-shrinkage concrete mixes.
Based on a limited review of bridges in Iowa and finite element modeling, Phares et al. (2015)
concluded that longitudinal and diagonal cracking in the deck on an integral abutment bridge in Iowa

14
was caused by the restraint of the abutment and the temperature differences between the abutment
and the deck. Although not likely to induce cracking, shrinkage of the deck concrete may have exac-
erbated cracks that developed from thermal effects. Longitudinal and diagonal cracks were prevalent
in integral abutment bridges but not as prevalent in bridges with stub abutments. Bridge width and
skew had minimal effect on the bridge deck strain resulting from restrained thermal expansion. Pier
type, girder type, girder spacing, and number of spans also appeared to have no influence on the level
of restrained thermal expansion strain in the deck near the abutment.
Based on research for the Indiana DOT, Frosch et al. (2002) recommended that the total amount
of reinforcing steel, As, to control crack widths in concrete bridge decks should satisfy the following
equation:
f c′
As ≥ 6 Ag (1)
fy
where
Ag = gross area of concrete section (in.2);

As = area of reinforcement in the cross-section (in.2);
f ′c = specified compressive strength of concrete (psi); and
fy = specified yield strength of reinforcement (psi).
The purpose for this quantity of reinforcement is to prevent yielding of the reinforcement that can
result in uncontrolled crack growth. For a 4.0-ksi concrete compressive strength with a 60-ksi yield
strength reinforcement, this requirement results in a reinforcement percentage of 0.63 or 0.61 in.2/ft in
an 8-in.-thick deck. This compares with 0.27 in.2/ft and 0.18 in.2/ft for bottom and top layers, respec-
tively, required by the empirical design procedure of the AASHTO LRFD Specifications (AASHTO
2016). Frosch et al. (2002) also recommended a maximum bar spacing of 6 in. to control crack widths.
In contrast, the Texas DOT recently reduced the amount of reinforcement used in the top mat of
reinforcement in concrete bridge decks 8 in. and 8.5 in. thick (Holt 2014). Previously, No. 5 bars at
a 6-in. spacing were used in the transverse direction and No. 4 bars at a 9-in. spacing in the longitu-
dinal direction. The new requirement is No. 4 bars at 9-in. spacing in both directions, supplemented
with short No. 5 bars at 9-in. spacing in the overhang portions to ensure adequate strength for the
overhang and forces on the traffic railings. The selection of a 9-in. spacing for the top mat was based
on inspections and observations of in-service decks where adequate crack control was being obtained
by using No. 4 bars at 9-in. spacing in the longitudinal direction. This is equivalent to 0.27 in.2/ft
or 50% more than 0.18 in.2/ft required by the AASHTO specifications for top bars in the empirical
design method.
Riding et al. (2009) measured concrete and ambient temperatures during the casting of a bridge
deck in Austin, Texas, in August 2006. The measured temperature at middepth of the deck ranged
from about 85°F at time of concrete placement to a maximum of about 123°F. The measured tempera-
tures were then used in the laboratory with restrained specimens to determine the induced concrete
stresses in a variety of concrete mixes. The testing revealed that the early-age thermal stresses were
reduced by as much as 50% when a coarse aggregate with a lower coefficient of thermal expansion
was used. A simulation of casting the concrete late at night versus in the morning also reduced the
tensile stresses.
In 2011, the Washington State DOT introduced a performance-based specification to reduce

cracking in their bridge decks (Gaines and Sheikhizadeh 2013). Instead of placing requirements on
minimum cementitious material content, the new mix has the following requirements:
• 28-day concrete compressive strength not less than 4.0 ksi;

• 28-day drying shrinkage of 320 millionths per AASHTO T 160;
• 56-day rapid chloride permeability of 2,000 coulombs per AASHTO T 277; and
• Scaling resistance with a visual rating less than or equal to 2 after 50 cycles per ASTM C672.

15
Although implementation of the new specifications reduced deck shrinkage cracking, minor
cracking was still evident. This was attributed to the differential temperature between the deck peak
hydration temperature and the ambient temperature. Gaines and Sheikhizadeh (2013) indicated that
strain caused by this temperature differential can be as much as 300 millionths. A differential tem-
perature limited to 24°F maximum has resulted in a significant reduction in transverse deck cracking.
The Washington state performance-based approach is discussed in chapter seven.
In Pennsylvania, data from a field investigation of 203 bridge decks were used to identify factors
that contribute to early-age cracking and to assess the effect of cracks on the long-term durability of
bridge decks (Manafpour et al. 2016). The following main conclusions were reported:
• Higher concrete compressive strengths resulted in higher crack densities. A maximum allow-
able concrete strength of 4.0 or 5.0 ksi at 7 or 28 days, respectively, was suggested.
• Lower total cementitious materials content and higher quantities of SCMs resulted in less
cracking. A maximum cementitious materials content of 620 lb/yd3 and the use of SCMs to
reduce heat of hydration were suggested.
• Decks constructed with half-width procedures to allow one half of the bridge to remain open
cracked four times more often than did decks constructed with the full-width cast at one time
and the use of traffic detours.
Lwin and Russell (2006) recommended the following practices to reduce cracking in concrete
bridge decks:
• Decrease the volume of water and cementitious paste consistent with achieving other properties.
• Use the largest practical maximum size aggregate.
• Use aggregates, when locally available, that result in a lower concrete shrinkage.
• Use the smallest transverse bar size and minimum spacing that are practical.
• Avoid high concrete compressive strengths.
• Design the concrete mix to produce a low modulus of elasticity and high creep.
• Implement surface evaporation requirements and use windbreaks and fogging equipment,
when necessary, to minimize surface evaporation from fresh concrete.
• Apply wet curing immediately after finishing and cure continuously for at least 7 days.
• Apply a curing compound after the wet curing to slow the shrinkage and enhance the concrete
properties.
Partial-Depth, Precast Concrete Panels with a Cast-in-Place Topping
This bridge deck system consists of precast concrete panels that span between the top flanges of
adjacent steel or concrete beams. The panels generally are pretensioned in the direction of their span
and initially supported on bearing strips along the beam flanges. Below casting the topping, it is
important that the precast panel top surface be thoroughly cleaned and saturated with water without
ponding. The CIP deck placed over the beams and panels forms the complete deck and makes a
composite system of the CIP concrete deck, precast panels, and the bridge beams. The system is often
used to accelerate bridge deck construction.
In the survey for this synthesis, agencies were asked about the frequency of cracking in CIP con-
crete decks on precast concrete deck panels. The results are summarized in Figure 4, which indicates
that less than half of the agencies use partial-depth precast concrete panels and that cracking occurs
slightly more frequently than infrequently.
In Texas, this system has been used extensively where the design has been standardized. Lon-
gitudinal cracking over the girders has been reported as the most significant problem associated
with the use of partial-depth concrete panels because it can result in a reduction in deck stiffness
over the girders, which could compromise the deck’s load-transfer mechanism (Merrill 2002). The
cracks have been caused by insufficient support of the panels on the beams and shrinkage of the CIP
concrete being restrained by the precast concrete panels. Shrinkage of the CIP deck concrete and
panel restraint have also led to transverse cracking. The widths of longitudinal and transverse cracks

16
FIGURE 4 Frequency of cracking with partial-depth, precast

concrete panels.
are controlled by the reinforcement in the CIP concrete. In comparative laboratory tests, Tsui et al.
(1986) showed that a deck with partial-depth panels was stronger, stiffer, and more crack-resistant
than a deck with full-depth, CIP concrete.
As part of their inspection of 19 HPC bridges, Mokarem et al. (2009) reported the inspection of
three bridges that used precast, prestressed concrete panels supporting a composite CIP concrete
deck. The three bridges that included panels are the Route 3A Bridge in New Hampshire and the
Louetta Road and San Angelo bridges in Texas.
The New Hampshire Route 3A Bridge uses four longitudinal NE 1000 simple-span girders spaced
at 11.5-ft centers and supporting 3.5-in.-thick precast concrete panels and a 5.5-in.-thick CIP com-
posite concrete deck. Cracking in the main span of the bridge consisted of five cracks with a total
length of 18.5 ft. This was a low amount of cracking and indicates that the use of precast concrete
deck panels is not always a contributing factor in bridge deck cracking.
The Texas Louetta Road Bridge consists of separate northbound and southbound structures. Both
structures use precast, prestressed concrete U-beams supporting 3.5-in.-thick precast concrete deck
panels and a 3.75-in.-thick composite CIP concrete deck. Beam spacing varies from 11.5 to 16.6 ft. The
panels span between the two top flanges of individual beams as well as between the flanges of adjacent
beams. The specified concrete strengths for the CIP decks on the northbound and southbound structures
were 4.0 ksi at 28 days and 8.0 ksi at 28 days, respectively. Measured compressive strengths were about
5.7 ksi at 28 days for the northbound structure and about 9.1 ksi at 28 days for the southbound structure.
Overall, both structures exhibited a similar and relatively high total cracking density, with the north-
bound having less transverse cracking and more longitudinal cracking than the southbound bridge.
Most of the longitudinal and transverse cracking appears to occur above the edges of the precast deck
panels and occurs throughout the length of each span. Factors that contribute to this cracking could be
shortening of the precast panels as a result of creep and differences in the coefficient of thermal expan-
sion between the CIP concrete and the precast panel concrete. It appears that the different concrete
strengths used in the two bridges did not play a significant role in the amount of cracking in the decks.
The Texas San Angelo Bridge consists of separate eight-span eastbound and nine-span westbound
structures. Both structures consist of precast, prestressed concrete I-beams supporting 4.0-in.-thick
precast concrete deck panels and a 3.5-in.-thick composite CIP concrete deck. AASHTO Type IV
beams are used for most spans with Texas Type B beams for two short spans. Beam spacing varies
from 5.4 to 11.0 ft. For the eastbound structure, HPC was used for the beams, panels, and CIP con-
crete deck, except for the CIP deck of spans 6 through 8. For the westbound structure, HPC was used
only for the CIP deck of spans 1 through 5.

17
Overall, both structures exhibited the largest total crack density of the 19 bridges included in the
investigation (Mokarem et al. 2009). However, the total crack density in the eastbound structure was
about 60% of that in the westbound structure. In both structures, about 65% of the cracking occurred
in the transverse direction. Similar to the Louetta Road Bridge, the presence of the precast concrete
panels influenced the location of the cracks.
Of the 17 spans included in both structures, eastbound spans 1 through 4 exhibited the least total
crack density. All four spans are rectangular in plan. Spans 1 through 3 have a constant beam length and
spacing. Span 4 has a slightly variable beam length to accommodate a change in the roadway width and
skew angle of the bents. Spans 2 through 4 are the longest three spans in the bridge. By contrast, east-
bound spans 5 through 7 are shorter and have a larger change in beam spacing and length; in addition,
there is a large skew at the end of span 7. Most of the cracking, which is transverse, occurred above the
beams with the longer span lengths. In addition, span 7 is relatively short but has a large skew at one
end and exhibited the second highest total crack density in all of the bridge spans inspected. Westbound
span 9, which has a square abutment on one end and skew bent at the other, had the highest total crack
density. These observations indicate that bridge geometry influences the amount of concrete cracking,
particularly when the geometry results in torsional stresses.
In Missouri, several bridge decks with partial-depth panels were observed to have spalling on
the underside at the edges of the panels (Spraggs et al. 2012). A detailed investigation indicated
that reflective cracking in the deck above the transverse joints had allowed water and chlorides to
penetrate to the interface between the CIP concrete and the precast concrete panels. The water then
penetrated into the precast panel causing corrosion of the prestressing strand located nearest to the
panel joints.
According to Kwon et al. (2014), approximately 200,000 ft2 of deck panels composed of 3,000
pieces measuring 8 ft by 8 ft by 4 in. are rejected annually in Texas because of cracking during fab-
rication, handling, or transporting. The most common cracks form above and below the prestressing
strands after strand release. The researchers determined that the likelihood of this type of cracking
could be reduced by lowering the initial strand stress from 189 to 169 ksi.
The weakness of the system is the reflective cracking that occurs and allows water and chlorides
to penetrate into and below the deck. Research is needed to identify the primary factors causing the
reflective cracking and ways to reduce or eliminate it.
Full-Depth, Precast Concrete Panels
In the full-depth, precast concrete deck system, panels span transversely across several bridge beams,
as shown in Figure 5. The length of a panel along the roadway is usually 8 to 12 ft. The width of a
FIGURE 5 Erection of full-depth, full-width, precast concrete panels

[Courtesy: ENTRAN PLC (now Stantec) and ASPIRE–
The Concrete Bridge Magazine].

18
panel is usually the full width of the bridge, unless that makes the panel too long or heavy to ship
or staged construction is used. The panels generally are pretensioned in the transverse direction and
may be posttensioned in the longitudinal direction. The panels usually are made composite with the
beams using studs or reinforcement as shear connectors. The shear connectors fit into pockets in the
panels. Grouting the pockets accomplishes the composite action [Precast/Prestressed Concrete Insti-
tute (PCI) 2011]. The use of precast panels facilitates faster construction for deck replacements and
new construction.
The advantage of a full-depth panel system is the prestressing in two horizontal directions,
which reduces the likelihood of cracking. For simple span bridges, the PCI State-of-the-Art
report (PCI 2011) suggests a precompression across the transverse joint between panels of
0.250 ksi after all losses. For continuous spans, the amount is 0.300 to 0.850 ksi, depending
on the magnitude of the negative moment. On Nebraska’s Skyline Bridge (Fallaha et al. 2004),
the precompression across the transverse joints from the longitudinal posttensioning was about
0.800 ksi. This allowed for no tension in the deck even in the negative moment regions over the
piers. Swenty et al. (2014) recommended that the transverse joints have sufficient prestressing
force across them to limit the tensile stress to a maximum of 3√f ′c psi under superimposed dead
loads and live loads. Carter et al. (2007) reported that Wisconsin’s first full-depth precast panel
bridge had no cracks of any kind 1 year after completion. Other installations are described in
PCI (2011).
In addition to the panels being designed to carry live load and superimposed dead loads, it is
important that the stresses during lifting and shipping be checked to ensure that the panels do not
crack under such loading conditions.
In the survey for this synthesis, slightly less than half the agencies reported on the frequency of
cracking in full-depth, precast concrete deck panels. The results are summarized in Figure 6, which
indicates that cracks occur above the connections and at other locations. Apparently, the use of this
system has not always eliminated deck cracking.
A 2003 survey (Badie and Tadros 2008) identified that nine states had used full-depth panels in
the previous 10 years. In the survey for this synthesis, 16 states provided information about cracking
in full-depth panel systems.
30
25
20
No. of
Agencies
15
10
0
er
ly
ly
le
ay
w
nt
nt
ab
ev
no
lw
ue
ue
ic
N
nk
A
l
eq
eq
pp
U
fr
Fr
A
In
ot
N
FIGURE 6 Frequency of cracking in full-depth, precast concrete deck panels.

19
FIGURE 7 Longitudinal cracking in an adjacent box beam bridge

(Courtesy: New York State DOT).
Cracking in Adjacent Box Beam Bridges and Slab Beam Bridges
Adjacent box beam and slab beam bridges consist of precast, prestressed concrete beams that are
placed next to each other (Russell 2009). Adjacent units generally are connected by a longitudinal
grouted keyway. For box beams, transverse ties are incorporated to hold the beams together. The ties
may be grouted or ungrouted and vary from a limited number of nontensioned threaded rods to sev-
eral high-strength tendons posttensioned in multiple stages. A transverse diaphragm is provided at
the location of each transverse tie (Russell 2009). Adjacent slab beam bridges are similar to adjacent
box beam bridges, except the adjacent units are usually connected with reinforcement protruding
from the beams into the joint region between the adjacent units.
A noncomposite topping or a composite concrete slab may be added as the riding surface. The com-
posite topping contains transverse and longitudinal reinforcement to control cracking and provides
lateral transfer of shear between adjacent beams or slabs. According to a 2008 U.S. survey, approxi-
mately two-thirds of the states use adjacent box beam construction (Russell 2009). As illustrated in
Figure 7, longitudinal cracking occurs at the location of the joint between the adjacent box beams. The
transverse ties and composite topping, if used, are provided to control this type of cracking.
In the survey for this synthesis, agencies provided information about the frequency of cracking
with this system. The results are shown in Figure 8. It appears that the frequency of cracking is about
the same for a system with and without a CIP concrete deck.
FIGURE 8 Frequency of cracking in adjacent box beam bridges.

20
Ahlborn et al. (2005) reported on an inspection of 15 box beam bridges in Michigan. Longitudinal
deck cracking reflecting from the shear keys was identified as the leading cause of distress. Similar
longitudinal cracking has been observed in slab beam bridges in Florida (Alfonso et al. 2006).
In a 2008 survey of state agencies, 76% of the respondents who used box beam bridges indicated
that the most common type of observed distress was longitudinal cracking along the grout and box
beam interface (Russell 2009). For bridges with a CIP topping, reflective cracks often were visible
in the riding surface. The impact of the cracking was to allow water and salt leakage through the
longitudinal joint. This was reported as the second most common type of observed distress. The
presence of longitudinal cracking in adjacent box beam bridges has been reported by others, as
described here.
Attanayake and Aktan (2008) reported that cracks along the shear key and box beam interfaces
were observed before and after transverse posttensioning. Fifteen days after the deck was cast,
through-thickness cracks that stemmed from the top surface of the deck above the abutments were
observed.
Mokarem et al. (2009) reported on the inspection of two adjacent precast, prestressed concrete
box beam bridges: one in Ohio and one in Colorado. The Ohio bridge consisted of a single span with
twelve 42-in.-deep box beams and a 3-in.-thick asphalt riding surface. With the exception of three
short diagonal cracks, the entire crack pattern consisted of longitudinal cracks.
The Colorado bridge consisted of two spans with twenty-four 29.5-in.-deep box beams and a
6.9-in.-thick CIP concrete deck with a 3- to 4-in.-thick asphalt overlay. No visible leakage on the
underside of the box beams was observed during the inspection. The lack of visible cracking above
the edges of the box beams may have been the result of using a 6.9-in.-thick CIP concrete deck that
acts as a transverse tie.
Stringer and Burgueno (2012) reported that longitudinal cracking was common in bridges in
Michigan with both adjacent box beams and spread box beams. The cracks typically ran the entire
length of the bridge and were spaced at the same spacing as the beams. The longitudinal cracks
in the adjacent box beam bridges likely were caused by differential settlement between the beams
and the grout filler or loss of the transverse posttensioning force between the beams. For the
spread box beam bridges, longitudinal cracking likely occurred because of a concentration of
longitudinal shear forces at the edges of the beams. This was predicted because the spacing of the
cracks matched the beam spacing. These types of cracks were not caused by restrained concrete
shrinkage. Transverse cracking was not evident in adjacent box beams but was present in spread
box beam bridges.
A Precast/Prestressed Concrete Institute report (PCI 2012) confirms that the predominant distress
observed in adjacent box beam bridges is reflective cracking of the deck along the shear keys between
beams and the associated degradation below the cracks. The cracking allows water and deicing salts
to penetrate through the deck and may cause freeze-thaw damage or corrosion of the transverse tie.
Researchers differ on the causes of the longitudinal cracks. Miller et al. (1999) reported that stresses
caused by temperature changes crack the keys along the interface. Grace et al. (2012) concluded that
a positive temperature gradient (top surface hotter than the bottom surface) and not live load was the
major contributing factor in the initiation of longitudinal cracks. On the other hand, other researchers
have developed design procedures to prevent cracking on the basis of force transfer (El-Remaily
et al. 1996; Hanna et al. 2007; Badman and Liang 2007; Hansen et al. 2012). Field inspection data for
bridges in Michigan revealed that a high level of posttensioning force did not prevent reflective crack-
ing (Attanayake and Aktan 2008). In a study of New York State bridges, Lall et al. (1997) concluded
that the frequency of longitudinal cracking in adjacent box beam bridges was unrelated to maximum
span length, total bridge length, and bridge skew.
One practice that has the potential to eliminate the longitudinal cracking at the keyways is the
use of ultra–high-performance concrete (UHPC) as the grout between the adjacent box beams

21
(Graybeal 2014). UHPC has the ability to provide a much stronger bond strength with the precast
elements than do conventional grouts. The use of UHPC in connections together with a reinforce-
ment lap splice can provide a connection that is capable of transferring shear, moment, and axial
forces across the connection. The UHPC detail eliminates the need for transverse posttensioning or
a structural concrete overlay.
The Sollars Road Bridge over Lees Creek in Fayette County, Ohio, was the first box beam bridge
in the United States to use the UHPC detail. The bridge consists of seven 21-in.-deep by 48-in.-wide
adjacent box beams. No transverse posttensioning was provided, so the intermediate diaphragms
were eliminated. No cracking in the joint was observed before application of the waterproofing
membrane (Steinberg et al. 2015).
NCHRP Project 12-95 has the objective of developing guidelines for the design and construction
of connection details for adjacent precast concrete box beam bridges to eliminate cracking and leak-
age in the longitudinal joints between adjacent boxes.
Cracking in Pretensioned Concrete Beams
End Zone Splitting Cracks
End zone cracking occurs in pretensioned concrete girders during or after release of the pretensioned
strands. The strands may be released by flame cutting, gradual release using hydraulic jacks, or a
combination. The draped strands usually are released first and then the hold-down anchorage devices
at the harp points are removed. The straight strands are then released (PCI 2014).
Various types of end zone cracking have been observed, as illustrated in Figure 9. Cracking at the
ends of pretensioned girders is not a new phenomenon. In 1962, Marshall and Mattock reported that
horizontal web cracks had been observed at the ends of pretensioned girders. These cracks occurred
FIGURE 9 End zone cracks in a prestressed

concrete beam (Courtesy: University of
Wisconsin and Concrete Bridge Views, published
jointly by FHWA and the National Concrete
Bridge Council).

22
more frequently in girders with draped strands. Based on experimental research, the following equa-
tion was proposed to control the size of these cracks:
T h
At = 0.021 × (2)
fs lt
where
At = total cross-sectional area of stirrups required (in.2);

T = effective prestressing force (kip);
fs = maximum allowable stress in stirrups (ksi);
h = overall depth of the girder (in.); and
lt = strand transfer length (in.).
If h/lt is taken as 2, the maximum value for which the equation was developed, the equation reduces to
designing for about 4% of the prestressing force, which is the amount of splitting reinforcement required
by Article 5.9.4.4.1 (formerly 5.10.10.1) of the AASHTO LRFD Bridge Design Specifications (2017).
The authors recommended that this reinforcement be located as close as possible to the ends of the girder.
Based on the results of the survey for this synthesis, as shown in Figure 10, end zone splitting
cracks occur infrequently.
Mirza and Tawfik (1978) reported that narrow vertical cracks were observed at the ends of beams
during the prestressing transfer after approximately one-half of the strands had been detensioned.
The cracks were located within a few inches of the beam end and extended from the bottom of the
lower flange into a portion of the web. They determined that the restraining effect of unreleased
strands can cause the cracking. When some of the strands were cut, the beams shortened and cam-
bered, but the uncut strands restrained the shortening. Increasing the free length of the strand in the
bed or debonding some strands at the ends was proposed as a means for eliminating the cracking.
Kannel et al. (1997) reported vertical cracks similar to those reported by Mirza and Tawfik. The
cracks occurred after the draped strands were cut and before any straight strands were cut. They also
reported that diagonal cracks at an angle of 45 degrees formed in the tapered portion of the bottom
flange during cutting of the straight strands. Short horizontal cracks also formed at the web-to-bottom
flange intersection during cutting of the final strands. The straight strands were flame cut from the
outside face of the flange toward the center of the beam. The cause of the cracks was attributed to the
restraining effect of unreleased strands as the girders shorten from the partially transferred prestress
and from shear stresses generated by the cutting order of the strands (Kannel et al. 1997).
FIGURE 10 Frequency of end splitting cracks.

23
Based on analytical and experimental research, Kannel et al. (1997) recommended the following
sequence for cutting strands:
• Cut some of the bottom straight strands before all of the draped strands. A general rule of thumb
is to precut one pair of straight strands for every three pairs of draped strands.
• Cut the bottom straight strands in alternating columns from the interior of the cross section
toward the outside face. The outer column of strands should not be the last to be released.
• Where debonding is used to control cracking, cut a few straight strands first.
According to Cook and Reponen (2008), six types of cracks were evident during site visits to three
Florida manufacturers of precast, prestressed concrete beams.
• Vertical end cracks: These cracks appear on the vertical face of the bottom flange within a few
inches of the end of the beam.
• Radial cracks: These cracks form a radial pattern that extends over the full depth of the web at
the end of the beam. The authors attribute this cracking to the change in support location when
the beams are lifted. Before the beams are lifted, the support is below the bottom flange. When
lifted through lifting hooks, the lifting location moves to the top of the beam.
• Angular cracks: These cracks originate in the sloped part of the bottom flange a few inches
away from the end of the beam and propagate upward at an angle toward the web. These are
similar to the cracks discussed by Kannel et al. (1997).
• Strand cracks: These cracks originate at the end of the prestressing strand and propagate to the
outer surface of the beam. The authors attribute the causes of these cracks to a combination of
the Hoyer effect, strand rust occurring after casting, and the strand cutting pattern.
• Horizontal top flange cracks: These cracks begin at the end face of the upper flange and move
inward. Field personnel indicated that these cracks are caused by formwork pressing against
the beam as it cambers during transfer.
• Horizontal web cracks: These cracks begin at the end of the beam near the interface between
the web and the bottom flange and extend a short distance into the beam.
The authors’ primary recommendation to reduce vertical end cracks was to install steel bearing plates
at the beam ends to reduce the friction force that develops between the end of the beam and the cast-
ing bed. Florida now uses galvanized bearing plates in all I-beams.
Field surveys of the ends of pretensioned concrete bridge beams in Virginia indicated that many
of the precast bulb-tee beams developed cracks within the anchorage zone region (Crispino et al.
2009). The lengths and widths of these cracks ranged from acceptable to poor and in need of repair.
Field observations also indicated deeper cross sections, heavily prestressed sections, and beams with
lightweight concrete tended to be most susceptible to crack formation. Based on their analyses, the
authors developed design tables that provide the area of stirrups required within h/4 and between h/4
and 3h/4 from the end of the beam, where h is the depth of the beam.
Ronald (2015) has stated that bearing zone tearing cracks will not occur in every beam, only those
in which the friction force exceeds the tensile strength of the concrete. The problem can be eliminated
by using bearing plates, but there are likely thresholds that can be quantified to avoid the problem in
less heavily stressed girders. Detensioning of all prestressing strands at the same time may also prove
to be as effective as steel bearing plates in eliminating these cracks.
In NCHRP Report 654, Tadros et al. (2010) identified the following possible causes for end zone
cracking:
• Method of detensioning: flame cut or hydraulic.

• Release of the top straight or draped strands before the bottom straight strands.
• Order of release of bottom strands with flame cutting.
• Length of free strand in the prestressing bed.
• Friction between the beam end and the bottom form of the prestressing bed.
• Heat concentration from flame cutting.

24
• Lifting the beam from the bed.

• Hoyer effect.
• Use of larger diameter strands.
• Inadequate design of end zone reinforcement.
• Concrete type: lightweight or normal weight.
• Strand distribution: draped or straight.
Based on the results of structural testing of eight full-scale girders and field inspection of five
bridges, the following proposed crack width limits were developed for acceptance, repair, or rejection
of beams with web splitting cracks at the ends of beams (Tadros et al. 2010):
• Cracks narrower than 0.012 in. may be left unrepaired.

• Cracks ranging in width from 0.012 to 0.025 in. should be repaired by filling the cracks with
approved specialty cementitious materials and coating the end 4 ft of the beam web side faces
with an approved sealant.
• Cracks ranging in width from 0.025 to 0.050 in. should be filled by epoxy injection and the end
4 ft of the beam web coated with an approved sealant.
• For beam webs exhibiting cracks wider that 0.050 in., the beams should be rejected unless shown
by detailed analysis that the structural capacity and long-term durability are sufficient.
The report also recommended that vertical splitting reinforcement at the ends of prestressed con-
crete beams be provided to resist at least 2% of the prestressing force at transfer and located within
the distance h/8 from the end of the beam, where h is the overall depth of the precast member. In
addition, the total amount of vertical reinforcement located within the distance h/2 from the end of
the beam shall be provided to resist at least 4% of the prestressing force at transfer. The existing
requirement of the AASHTO LRFD Specifications is that reinforcement to resist 4% of the prestress-
ing force at transfer be distributed over a distance of h/4.
Ross at al. (2013) conducted experimental and analytical research programs to evaluate and quan-
tify the effects of different end region detailing practices on end zone cracking. The programs included
the testing of 14 Florida I-beam specimens and finite element analyses. The authors concluded that the
Florida DOT’s confinement reinforcement requirement is adequate for beams to at least an FIB-63.
The current detail generally requires No. 3 bars at 3.5-in. spacing over a distance of approximately
0.3d from the end of the beam and then No. 3 bars at 6-in. spacing to a distance of approximately 1.5d
from the end of the beam, where d is the distance from the compression face to the centroid of the
tension reinforcement. Florida DOT (2016) has design standards detailing the reinforcement for each
beam type and size. The current detail also includes an embedded steel bearing plate, which functions
as a confining element.
For the use of partially debonded strands, Ross et al. (2013) recommended that the fully bonded
strands be placed as close as possible to the centerline of the web to prevent bottom flange split-
ting cracks. They also indicated that the AASHTO limitation of no more than 40% of the debonded
strands, or four strands, whichever is greater, be terminated at any section should control flange
splitting cracks within the transfer length.
To prevent or control web splitting cracks, Ross et al. (2013) recommended that the Florida DOT
requirement of vertical end region reinforcement be used. This requirement is generally two No. 5
bars at 3.5-in. spacing over a distance of approximately 0.3d from the end of the beam and then two
No. 5 bars at 6-in. spacing to approximately 1.5d from the end of the beam, where d is the distance
from the compression face to the centroid of the tension reinforcement. Florida DOT has design
standards detailing the reinforcement for each beam type and size.
Okumus and Oliva (2013) identified three types of cracking in the ends of prestressed concrete
girders, as shown in Figure 9. These were inclined longitudinal cracks in the webs, horizontal longitu-
dinal cracks in the webs, and Y- and T-shaped cracks at the web-bottom flange intersection as seen at
the ends of the girders. They evaluated methods to control these cracks using nonlinear finite element
analysis methods. Results were compared with the observed crack patterns. The most effective crack

25
control methods were debonding the strands at the ends rather than using draped strands, locating
the lifting loops at a distance equal to the girder depth from each end, and detensioning the strands
beginning with the innermost ones.
Increasing the vertical reinforcement area in the end zone alone was not recommended because
it did not eliminate cracking, although it did help control crack widths. The two sets of bars clos-
est to the girder end were determined to be the most effective bars in controlling the size of
cracks in the webs. Additional bars further into the section were not useful in controlling web
crack widths.
For strand debonding, the authors recommended that the innermost strands of the bottom flange
should be fully bonded and the rest of the bonded strands evenly distributed across the bottom flange.
Debonding the strands within 12 in. of the end of the girders was highly recommended to control
horizontal web and Y cracks. However, this approach results in the end of the beam being nonpre-
stressed, a practice that may not be acceptable by state bridge engineers. It also makes it more dif-
ficult to satisfy the longitudinal reinforcement requirements of Article 5.7.3.5 (formerly 5.8.3.5) of
the AASHTO LRFD Bridge Design Specifications.
Shear Cracks
Compared with the number of publications about cracking in bridge decks and cracking at the ends
of prestressed concrete beams, there are few publications about shear cracks in prestressed concrete
beams in actual bridges. This probably is because the principal tensile stress in the web of a prestressed
concrete beam at service load does not exceed the tensile strength of the concrete. To ensure that shear
cracks do not occur with the use of higher strength concretes, the eighth edition of the AASHTO LRFD
Bridge Design Specifications (AASHTO 2017) requires that the principal tensile stress in the webs of
pretensioned girders with a compressive strength of concrete for use in design greater than f c′ = 10.0 ksi
shall not exceed 0.110l√f c′ when the superstructure element is subjected to the loadings of Service III
limit state, where l = concrete density modification factor.
Cracking Before Transfer
Vertical cracks extending the full depth of the webs of precast, prestressed concrete beams have
been observed to develop before transfer of the prestressing force. These cracks generally are in
the midspan region of the beam and are more prevalent in deep, long-span beams that have higher
strength concrete and a large quantity of prestressing strands (Baran et al. 2004). They are more
likely to occur if the beams are left in the precasting bed for a longer time period between the end of
heat curing and transfer of the prestressing force. The cracks close up and may not be visible after
the prestressing force is transferred.
The cause of these cracks has been attributed to shortening as the beams and exposed strands
between the beams cool. This shortening is restrained by the strands that are anchored at both ends
of the bed. As a result, tensile stresses develop in the beam before transfer of the prestressing force.
The likelihood of these cracks occurring can be reduced by providing sufficient free lengths of
strand between adjacent beams and between the end beams and the abutments in the casting bed. A
prolonged period of time between form stripping and transferring the prestressing force should be
avoided (Zia and Caner 1993; Baran et al. 2004).
Based on the survey for this synthesis, as shown in Figure 11, vertical cracks occur infrequently
before transfer.
Cracking in Nonprestressed Concrete Beams
In the survey for this synthesis, 11 agencies reported that cracking occurred infrequently or never in
nonprestressed concrete beams. Eight agencies reported frequent cracking, and 25 agencies reported
they did not know or the question was not applicable.

26
FIGURE 11 Frequency of vertical cracking before transfer.
Flexural cracking in nonprestressed concrete beams is inevitable because cross sections are
designed to be cracked. Crack control is provided by using a minimum amount of reinforcement and
a maximum bar spacing.
According to Higgins et al. (2004), approximately 500 CIP, reinforced concrete deck-girder
bridges in the Oregon DOT inventory are identified as exhibiting diagonal-tension cracking. Most of
the cracked bridges were built between 1947 and 1962. The cracks were attributed to an overestima-
tion of the concrete contribution to shear that was permissible in the design specifications at the time.
Subsequently, revisions were made to the specifications to alleviate the cause of the cracks.
Shear cracking in some nonprestressed substructures is discussed in the next section.
Cracking in Substructures
Cracking in substructures appears to be uncommon but can occur, as illustrated in Figure 12. In
the survey for this synthesis, 28 agencies identified that they use the same crack control criteria for
substructures that they use for superstructures. Eleven agencies use different criteria. These include
FIGURE 12 Cracking in a bent cap (Courtesy: Florida DOT).

27
different concrete mixes, shorter curing period, or a different exposure factor in Equation 5.6.7-1
(formerly 5.7.3.4-1) of the AASHTO LRFD Specifications (AASHTO 2017).
Pier or Bent Caps
As part of the survey for this synthesis, 31 agencies responded that cracking in pier caps occurred
infrequently or never. Ten agencies identified that their bridges had experienced frequent cracking
in pier caps, and one agency identified that cracking always occurred. The cracking was attributed
to shrinkage, shear, flexure, or temperature. One agency mentioned that the design stress for flexural
reinforcement in all substructures under Service III loading is limited to a maximum of 24 ksi.
Fu et al. (1992) reported that cracks occurred in eight pier caps of the Governor Thomas Johnson
Memorial Bridge in Maryland. The bridge was opened to traffic in December 1977, and the cracks were
observed during the first inspection in October 1979. It was subsequently determined that the tension
reinforcement was inadequate for the design condition. The design had used working stress design
assuming simple flexural behavior, whereas the behavior was predominantly one of shear in a deep beam.
Top and side face cracking at outside column locations in reinforced bent caps has been reported
for bridges in Texas (Bracci et al. 2000). This cracking, as illustrated in Figure 13, occurs under ser-
vice load conditions and, in some cases, is initiated under dead load alone. Based on experimental
and analytical research, the researchers recommended that the stress in the longitudinal reinforce-
ment under service load be limited to 36 ksi for moderate exposure and 30 ksi for severe exposure
conditions. In addition, horizontal side face reinforcement should be provided within the web tension
region per the AASHTO Specifications.
To control cracking in structures or regions thereof designed by the strut-and-tie method, the
AASHTO LRFD Bridge Design Specifications (AASHTO 2017) require the use of orthogonal grids
of bonded reinforcement. The spacing of the bars in these grids shall not exceed the smaller of d/4
and 12.0 in., where d is the effective depth of the member, and the reinforcement shall be distributed
evenly near the side faces of the strut. This reinforcement is intended to control crack widths and
ensure a minimum ductility for the member.
Columns
As part of the survey for this synthesis, 35 agencies responded that cracking in columns and abut-
ments occurred infrequently or never. Six agencies reported that their bridges had experienced
FIGURE 13 Diagonal cracking in a nonprestressed, concrete bent

cap (Courtesy: Texas DOT).

28
frequent cracking in columns or abutments, and one agency reported that cracking always occurred.
The cracking was identified as being caused by flexure, shear, shrinkage, formwork settlement, or
foundation settlement. Columns are generally in compression. Thus, it is unusual for them to expe-
rience cracks under service loads.
Pile Caps
Most pile caps tend to be relatively large components in bridge construction. As such, they are suscep-
tible to cracking caused by the heat of hydration of the cementitious materials. The likelihood of this
cracking can be reduced by control of the temperature differential between the surface concrete and
the interior concrete temperature. Cooling of the surface concrete can be prevented through the use of
surface insulation. The temperature rise of the internal concrete can be controlled by using cementi-
tious materials that produce a low heat of hydration, such as fly ash, and lowering the temperature
of the concrete at the time of placement through the use of ice or liquid nitrogen, the use of internal
cooling pipes, or a combination of these methods.
Specifications for larger projects generally require that the contractor develop a thermal control
plan showing how thermal cracking will be controlled. A chart indicating when concrete should be
considered mass concrete has been developed by Gajda and Feld (2015).
As part of the survey for this synthesis, 32 agencies reported that cracking in concrete pile caps
occurred infrequently or never. Several agencies reported that their bridges experienced minor crack-
ing in concrete pile caps. In general, the cracking was associated with shrinkage and temperature and
occurred infrequently.
Effective Practices for Control of Concrete Cracking
Two general approaches for crack control are possible. The first approach is to prevent the cracks.
This is a goal that may not always be achievable. The second approach is to ensure that adequate
reinforcement is present to control crack widths if cracking occurs.
Full-Depth, Cast-in-Place Concrete Bridge Decks
Many factors are known to affect deck cracking, including bridge design; concrete mixture propor-
tions; concrete constitutive materials; environmental conditions; and placing, finishing, and curing
practices. Studies have shown that the primary causes of bridge deck cracking are shrinkage (plastic,
autogenous, and restrained drying) and temperature differences between the deck concrete and the
supporting beams.
Practices that can reduce shrinkage and associated shrinkage cracking in CIP concrete bridge
decks are as follows:
• Using the lowest quantity of water and cement paste in the concrete consistent with achieving
other required properties.
• Using the largest practical maximum size coarse aggregate to reduce the water demand.
• Avoiding concrete compressive strengths greater than 6.0 ksi.
• Specifying a minimum shrinkage of 300 to 350 millionths after 28 days of drying when tested
in accordance with AASHTO T 160.
Practices that can reduce cracking caused by temperature differences include the following:
• Minimizing the temperature difference between the CIP concrete deck and the supporting steel
or concrete beams.

29
• Specifying and ensuring minimum and maximum concrete temperatures at the time of placement
as 55°F and 75°F, respectively.
• Minimizing cement content.
• Using a Type II cement.
• Using aggregates with low modulus of elasticity, low coefficient of thermal expansion, and high
thermal conductivity.
Construction practices that can reduce the likelihood of deck cracking include the following:
• Applying wet curing procedures immediately after concrete finishing and maintaining the surface
wet for at least 7 days.
• Applying a curing compound after the wet curing period to slow the shrinkage and enhance the
concrete properties.
• Using windbreaks and fogging equipment, when necessary, to minimize surface evaporation
from fresh concrete.
Other practices some agencies have used that offer potential solutions are the use of SRAs, internal
curing, and SCMs.
After cracking, crack widths can be controlled with appropriate amounts of reinforcement.
This is most effectively achieved with smaller bars and a specified maximum spacing of reinforc-
ing bars.
The main concern with the use of partial-depth, precast concrete panels with a CIP topping is the
reflective cracking that occurs in the topping above the edges of the panels. This type of cracking may
be reduced by saturating the surface of the panel before casting the topping, special joint detailing, and
delaying erection of the panels until most of the creep and shrinkage have occurred. Crack widths can
be controlled by the reinforcement in the topping. Research is needed to identify the primary factors
causing the reflective cracking and ways to reduce or eliminate it.
Although two-directional prestressing in full-depth, precast concrete panels offers the potential to pro-
duce a crack-free concrete deck, the results from the survey indicate that this is not always accomplished.
Research is needed on this topic to provide a solution for crack control.
Adjacent Precast Box Beam Bridges and Slab Beam Bridges
Lateral ties are used in adjacent precast box beam bridges to tie together adjacent beams. As such,
the ties function to control the crack widths. The degree of restraint varies from requiring a minimum
compressive stress across the longitudinal joint to providing a passive tie. NCHRP Project 12-95 has
the objective of developing guidelines for the design and construction of connection details for adja-
cent precast concrete box beam bridges to eliminate cracking and leakage in the longitudinal joints
between adjacent boxes. The use of UHPC is one potential solution.
Pretensioned Concrete Beams
End zone cracking in pretensioned concrete beams occurs infrequently and can be prevented by
modifying the detensioning sequence. Cracks that occur can be controlled through the use of split-
ting and confinement reinforcement in the end zone region. Vertical cracking that occurs in the webs
before transfer can be reduced by providing longer lengths of free strand in the prestressing bed.

30
Non-Prestressed Concrete Beams
Cracking in nonprestressed concrete beams is almost inevitable but is controlled by providing mini-
mum amounts of reinforcement to control the widths of cracks caused by flexure or shear.
Substructures
In general, cracking in substructures occurs infrequently. Limiting the maximum stress in the rein-
forcement under service loads provides a means of crack width control. Design of deep components
using the strut-and-tie method, rather than the sectional design method, along with the required
reinforcement should provide improved crack control. For large members, a thermal control plan
should be developed.

31
chapter three
Effects of Concrete Constituent

Materials on Cracking
Concrete constituent materials have an important impact on cracking, particularly in bridge decks,
because they affect the magnitude of shrinkage.
Concrete Constituent Materials for Bridge Decks
The primary benefit achieved by careful selection of concrete constituents is the reduction in drying
shrinkage and the associated reduction in cracking. This section summarizes practices and recom-
mendations that have been made to reduce shrinkage and concrete cracking in bridge decks.
General
Forty-eight bridge decks containing 10 different concrete mixes were inspected in Ohio for deck crack-
ing on the top and bottom surfaces (Lefchik 1994). The report noted that many decks showed varying
degrees of cracking over the surface of the deck with some isolated areas having more or less cracking.
In some cases, one end of a deck was relatively crack free, whereas the other end exhibited cracking. The
report concluded that factors other than concrete mix had a significant effect on the amount of cracking.
Krauss and Rogalla (1996) concluded that concrete material factors important in reducing cracking
include low shrinkage, low modulus of elasticity, high creep, low heat of hydration, and selection of
aggregates and concrete that provide a low cracking tendency. The material factors helpful in reducing
cracking included lower cement content, higher water-cement ratio, using shrinkage-compensating
concrete, and avoiding materials that produce high early compressive strengths and modulus of
elasticity values.
An evaluation of existing bridge decks in Kansas showed that cracking increased with increasing
values of slump, percent volume of water and cement, water content, cement content, and compressive
strength (Schmitt and Darwin 1995, 1999; Miller and Darwin 2000; Lindquist et al. 2005). Decreases
in cracking were noted with increases in air content. A study by North Carolina State University noted
a tendency for reduced cracking in the presence of higher slump and higher air concrete (Cheng and
Johnston 1985).
Based on a comprehensive literature search, Hadidi and Saadeghvaziri (2003) made the following
recommendations as positive steps to reduce the potential for deck cracking:
• Reduce cement content to 650 to 660 lb/yd3.

• Consider using a low early-strength concrete when early opening of the deck is not required.
• Limit the water-cement ratio to 0.40 to 0.45 or lower with the use of water reducers.
• Use the largest maximum aggregate size and the maximum aggregate content.
Menkulasi et al. (2015) recommended that a concrete mix for a CIP concrete deck should have
low shrinkage and high creep properties to reduce the likelihood of excessive cracking in bridge
decks. Low free shrinkage reduces the tensile stresses that develop because of restrained differential
shrinkage. High creep helps relax any tensile stresses that may develop. In addition, the short-term
properties that will help reduce the extent of cracking caused by differential shrinkage include a mix
with high tensile strength and low modulus of elasticity.

32
Because it is difficult to find a concrete mix that embodies all of these long-term and short-term
properties, priority should be given to a mix with the lowest shrinkage because it is the free shrinkage
of the deck that serves as a catalyst for the creation of tensile stresses in the CIP topping (Menkulasi
et al. 2015). Measurements on seven different concrete mixes showed that the mix with normal
weight coarse aggregate and saturated lightweight fine aggregate exhibited the lowest shrinkage
strain and the highest creep coefficient.
Before 2013, the Illinois Tollway used a prescriptive approach for mix proportioning and
had standard mixes for bridge decks (Gillen and Gancarz 2016). The mixes were made up of 605 to
705 lb/yd3 of cement, no SCMs or only small amounts of fly ash, and one coarse aggregate grada-
tion. Early-age cracking was seen on many bridge decks. In 2013, the Illinois Tollway introduced a
performance specification, which included requirements for linear shrinkage and restrained shrink-
age. Since 2013, 77 bridges have been built under the new provisions, and shrinkage cracking has
been reduced.
Cement
In the survey for this synthesis, agencies were asked to identify the frequency of use of different
cements in concrete bridge decks. Their responses are summarized in Table 3. Clearly, the most
frequently used cements are Types I and II.
The source of cement may have a large effect on drying shrinkage. Cements with high alkali con-
tent, high C3S and C3A contents, low C4AF, and high fineness have high strength gain and are found
to have higher cracking tendencies (TRB 2006). Thus, Type III cements should be used with caution
for deck applications. Some agencies restrict the use of Type III cements to precast concrete mem-
bers (Russell 2013). In an effort to control temperatures, Type II or Type IV cements, with their lower
heat of hydration, often are used in lieu of Type I cement, especially when warmer ambient condi-
tions exist. Slower-setting cements can be expected to have reduced drying shrinkage and cracking.
Decks constructed with Type II cement cracked less than did those constructed with Type I cement
(TRB 2006). The use of Type II cement was recommended by Saadeghvaziri and Hadidi (2002).
Krauss and Rogalla (1996) pointed out that the general chemistry of cements has changed over
time. In addition, today’s cements are finer than previous ones. Consequently, concrete made with
today’s cements gain strength more rapidly than did concrete made with previous cements. As a
result, modern concretes with a high early compressive strength and modulus of elasticity provide
an increased risk of cracking because of the high stresses that develop as a result of early shrinkage
and thermal strains.
One material that has been used in concrete bridge decks to reduce cracking is a shrinkage-
compensating concrete. A shrinkage-compensating concrete incorporates an expansive cement or
Table 3
Frequency of Use of Cements
Cement Never Sometimes Often Always

AASHTO M 85 Types I and IA 7 4 13 9
AASHTO M 85 Types II and IIA 3 6 13 11
AASHTO M 85 Types II(MH) and 19 3 6 1

II(MH)A
AASHTO M 85 Types III and IA 23 7 1 1

AASHTO M 85 Type IV 32 0 0 0
AASHTO M 85 Type V 29 2 1 0
AASHTO M 240 22 5 3 1
ASTM C1157 23 3 2 1

33
expansive component that causes the concrete to expand during the first few days. Thereafter, the
concrete shrinks in a manner similar to that of conventional concrete (ACI Committee 223 2010).
McLean et al. (2016) reported that approximately 600 bridge decks in the United States have been
built using shrinkage-compensating concrete.
The Ohio Turnpike is reported to have built more than 500 bridge decks using shrinkage-
compensating concrete, and cracking was reduced (Ramey et al. 1999). Gruner and Plain (1993) also
reported that the use of an expansive cement in place of a Type I portland cement on Ohio bridges
resulted in excellent performance.
The New York Thruway Authority placed 47 bridge decks from 1991 to 1994 using shrinkage-
compensating concrete. Most of the decks developed scaling problems to such an extent that the
authority discontinued the use of shrinkage-compensating concrete. An investigation of the causes
of the scaling determined that it had nothing to do with the use of shrinkage-compensating concrete
(Ramey et al. 1999).
Cope and Ramey (2001) investigated the use of shrinkage-compensating concrete with and without
silica fume and the use of an SRA to reduce early-age deck cracking. They concluded that the shrinkage-
compensating concrete without silica fume was a viable candidate for mitigating drying shrinkage crack-
ing. The Illinois DOT conducted laboratory tests of shrinkage-compensating concrete containing Type K
and Type G expansive components with and without SCMs (Chaunsali et al. 2013). Saadeghvaziri and
Hadidi (2002) also suggested the use of shrinkage-compensating concrete when available.
The Virginia DOT investigated the effectiveness of shrinkage-compensating concrete in reducing

cracks in bridge decks (Nair et al. 2016a). The bridge deck on the Route 613 Bridge over the South Fork
Shenandoah River in Warren County was selected for the study. The results showed that the bridge deck
with preblended Type K cement concrete had fewer transverse cracks than typically found in decks
constructed with Type I/II cement. There were several longitudinal cracks caused by the differential
movement at the keyway of the adjacent prestressed concrete box beams that could not be prevented
by the use of shrinkage-compensating concrete. Slump loss under hot weather conditions was a more
serious problem in shrinkage-compensating than in normal portland cement concrete.
Supplementary Cementitious Materials
Supplementary cementitious materials, such as fly ash, slag, and silica fume, are used frequently in
mixtures to enhance early and long-term performance characteristics (TRB 2006). In the survey for
this synthesis, agencies were asked to identify the frequency of use of different SCMs in concrete
bridge decks. Their responses are summarized in Table 4.
From these data, it appears that Class F fly ash is the SCM most frequently used in bridge
decks, and Class N pozzolan is used the least. This is similar to results obtained in a 2012 survey
(Russell 2013).
Fly ash and slag typically reduce the rate of strength gain, lower the heat of hydration, reduce
the rate of stiffness development, and thus typically reduce the potential for cracking (TRB 2006).
Table 4
Frequency of Use of Supplementary
Cementitious Materials
Material Never Sometimes Often Always
Fly ash Class C 11 11 13 3
Fly ash Class F 5 11 17 6
Pozzolan Class N 26 8 2 0
Silica fume 11 16 9 5
Ground-granulated
12 10 15 1
blast-furnace slag
Other 17 1 0 1

34
Yuan et al. (2015) reported that the use of slag cement as part of the cementitious materials
reduced the free shrinkage compared with mixtures containing only portland cement as the cementi-
tious material. When slag cement was used in combination with a porous limestone coarse aggregate,
an even greater reduction in free shrinkage was observed.
Silica fume can increase the rate of strength development, increase the heat of hydration, reduce
bleeding, and create conditions that are favorable for cracking. Some strongly discourage the use of
silica fume in bridge deck applications (Hopper et al. 2015); however, others have reported that silica
fume is not a cause of early cracking. According to Ozyildirim (1992), silica fume concrete is suscep-
tible to plastic shrinkage cracking because of its lack of bleeding. Therefore, immediate application
of sprays or misting after placement is essential to avoid the formation of plastic shrinkage cracks in
silica fume concrete.
According to laboratory tests by Whiting and Detwiler (1998), the cracking tendency of con-
crete was influenced by the addition of silica fume only when the concrete was improperly cured.
They recommended that specifications for silica fume concrete in bridge deck construction include
a provision for a 7-day continuous moist curing of exposed surfaces. Concretes containing silica
fume had somewhat higher shrinkages at early ages than did their counterparts not containing silica
fume. However, the long-term shrinkage of the silica fume concretes was not greater than identical
concretes without silica fume.
Aggregates
Most recommendations specify a maximum size aggregate of 1½-in. or the smaller of one-third
the deck thickness and three-fourths the minimum clear spacing between reinforcing bars (Krauss
and Rogalla 1996). A 1961 PCA study (PCA 1970) recommended the use of the largest practical
maximum size of coarse aggregate to minimize the water content to reduce cracking. Other recom-
mendations included use of the lowest reasonable slump and keeping the maximum slump within the
range of 2 to 3 in. Saadeghvaziri and Hadidi (2002) also recommended the use of the largest coarse
aggregate size and maximum aggregate content.
The use of soft aggregates, such as sandstone, results in increased drying shrinkage, whereas
the use of hard aggregates, such as quartz, dolomite, and limestone, results in decreased shrinkage
(TRB 2006).
The use of optimized combined aggregate gradations can result in the use of less water, less cementi-
tious materials, and thus less paste content (AASHTO 2010), which leads to less shrinkage. Optimized
combined aggregate gradations may be determined using the combined fineness modulus, coarse factor
chart, power chart, or percent retained on each sieve, as explained in the Appendix A8 of the AASHTO
LRFD Bridge Construction Specifications (AASHTO 2010).
The Virginia DOT investigated the performance of seven bridges with lightweight concrete decks
that were built between 2012 and 2014 (Nair et al. 2016c). The lightweight concrete contained
lightweight coarse aggregate and normal-weight fine aggregate. The concrete compressive strengths
ranged from 4.5 to 6.0 ksi at 28 days. The authors reported that some bridge decks had no cracks,
whereas others had fewer cracks than was typical of decks constructed with normal weight aggregate
over the past 20 years. Based on a field inspection, Ozyildirim and Moruza (2014) concluded that
lightweight, HPC bridge decks can be produced that have no visible cracking after 2 years in service.
Chemical Admixtures
Chemical admixtures can have a positive, negative, or no effect on concrete shrinkage and crack-
ing (TRB 2006). In the survey for this synthesis, agencies were asked about the frequency of use of
chemical admixtures, corrosion inhibitors, SRAs, and expansive cement or expansive components
for CIP concrete bridge decks. The respondents’ reported frequency of use of the admixtures is
shown in Table 5.

35
Table 5
Frequency of Use of Admixtures in Cast-In-Place Concrete Bridge Decks
Admixture Never Sometimes Often Always
AASHTO M 194 Type A—Water-reducing admixtures 2 7 15 14

AASHTO M 194 Type B—Retarding admixtures 4 20 10 3
AASHTO M 194 Type C—Accelerating admixtures 19 15 2 1
AASHTO M 194 Type D—Water-reducing and retarding

5 18 11 3
admixtures
AASHTO M 194 Type E—Water-reducing and accelerating
21 14 2 1
admixtures
AASHTO M 194 Type F—High range water-reducing admixtures 8 12 13 5
AASHTO M 194 Type G—High range water-reducing and

16 15 5 2
retarding admixtures
Corrosion inhibitors 25 11 2 1
Shrinkage-reducing admixtures 21 13 2 2
Expansive cement or components 30 8 0 0
The data indicate that agencies use a variety of the chemical admixtures specified in AASHTO
M 194, with Type A–water-reducing and Type F–high-range, water-reducing being used most fre-
quently and Type E–water-reducing and accelerating used the least. Corrosion inhibitors, SRAs, and
expansive cements or components are used by only a few agencies. The results shown in Table 5 are
similar to those obtained in a 2012 survey (Russell 2013).
An SRA has a positive effect by reducing the surface tension of the pore water and thus lowering
plastic and long-term shrinkage. Schemmel et al. (1999) reported that free shrinkage was reduced on
the order of 50% with the use of an SRA. However, the use of SRAs can affect air content, set time,
and bleed time (Kosmatka and Wilson 2016).
California Department of Transportation (Caltrans) found that the use of an SRA in the concrete
resulted in less shrinkage cracking in bridge decks (Maggenti et al. 2013). Beginning in the late
summer of 2002, Caltrans began using SRAs in their concrete deck mixes. As a result, there was a
dramatic reduction in cracking, and the decks remained free of visible cracking until at least 2013.
Given the agency’s positive experience with these and subsequent bridges, Caltrans has selected
SRAs as a method of crack control for CIP concrete decks on precast concrete girders. More details
about the Caltrans approach are provided in chapter seven.
Virginia DOT also investigated the effectiveness of SRAs in reducing drying shrinkage in concrete
mixtures and thus reducing cracks in bridge decks (Nair et al. 2016b). Nine bridges were selected for
study. Three different SRA products were used. With the exception of one mixture, the maximum
cementitious materials content was limited to 600 lb/yd3. The results showed that concrete with low
cementitious materials content and an SRA was effective in minimizing bridge deck cracking. The study
showed that bridges with fewer and narrower cracks or no cracks can be constructed and recommended
the use of an SRA and a cementitious materials content less than 600 lb/yd3 in Virginia DOT bridge deck
concrete mixtures. A special provision was developed for the future use of SRAs in concrete mixtures.
To provide the most effective resistance to drying shrinkage cracking in concrete bridge decks,
Brown et al. (2007) recommended that mixtures containing an SRA, polypropylene fibers, expansive
cement, or high volume fly ash be used.
Cementitious Materials Content and Water-Cementitious Materials Ratio
The most important factor affecting drying shrinkage is the amount of water per unit volume of
concrete (Kosmatka and Wilson 2016). Only about half of the water is used in the hydration process.

36
The rest is there to provide workability and finishability. The excess free water that remains in the
hardened concrete contributes to the drying shrinkage. Thus, shrinkage can be minimized by keep-
ing the water content as low as possible. For the same w/cm ratio, this also reduces the cementitious
materials content. Collectively, the paste content is reduced and the aggregate content is increased.
A study of premature cracking in concrete bridge decks for the Wisconsin DOT resulted in recom-
mendations to limit the water-cement ratio to a maximum of 0.40 and to use coarse aggregate with a
maximum size greater than 0.75 in. (Kochanski et al. 1990). Saadeghvaziri and Hadidi (2002) recom-
mended the use of a water-cement ratio between 0.40 and 0.45 and a cement content of 650 to 660 lb/yd3.
Responses to a Michigan DOT 2002 survey indicated that 52% of the 31 responding states use a
cement content of 658 lb/yd3 and 32% use 564 lb/yd3 in their bridge deck concretes (Aktan et al. 2003).
When the South Carolina DOT introduced a Class E concrete, they found that most of the bridge
decks experienced cracking occurring both before the bridge was opened to traffic and immediately
thereafter (Hussein 2006). After an investigation, the South Carolina DOT introduced a concrete mix
with less cementitious material, required that all bridge decks be wet cured for 7 full days, and wind
barricades and foggers be used during placement of all bridge deck concrete. The new mix resulted in
a concrete compressive strength of 4.0 ksi at 28 days. After implementation of the new requirements,
a few projects with HPC bridge decks were constructed without cracking. According to the authors, it
appears that the rich concrete mix was a major factor in causing the early-age cracking.
Based on their study of cracking in 19 concrete bridge decks, Mokarem et al. (2009) concluded that
a concrete mixture with a w/cm ratio between 0.35 and 0.40, a cementitious materials content between
600 and 700 lb/yd3, and appropriate construction practices, such as a 7-day wet curing, should be
expected to result in a lower crack density.
In their research to develop a low-cracking HPC, Darwin et al. (2012) recommended a maximum
cementitious materials content of 540 lb/yd3 and a w/cm ratio of 0.44 to 0.45.
Fibers
In the survey for this synthesis, 10 of 40 agencies reported that they had specified fibers as a strategy
to minimize cracking in concrete bridge decks. One agency listed the use of fibers as a strategy that
was most effective, whereas two agencies identified that it was the least effective.
ASTM C1116—Standard Specification for Fiber-Reinforced Concrete classifies fiber-reinforced

concrete into four different categories based on the material type of fiber: steel, glass, synthetic, and
natural. Fibers are beneficial in reducing bleeding and plastic settlement cracking in fresh concrete
and increasing energy absorption and load-carrying capacity after cracking (Kosmatka and Wilson
2016). Additional information about fibers is provided in ACI 544.1 (2009).
Several states now require the use of fibers in bridge decks. For example, Caltrans specifies that
each cubic yard of deck concrete must contain at least 1 lb of polymer microfibers and at least 3 lb
of polymer macrofibers. Microfibers must have a length from 0.5 to 2 in. Macrofibers must have a
length from 1.0 to 2.5 in. Oregon DOT specifies the use of synthetic fibers from the qualified prod-
uct list in all bridge deck concrete. The specified quantity differs according to the manufacturer’s
recommendations.
Concrete Constituent Materials for Other Components
Cracking in components other than bridge decks is generally less of a concern for owners because
the other components are exposed to a less severe environment than is the deck. In addition, the other
components are thicker than the deck, which reduces the magnitude and rate of shrinkage. The use of
continuous decks or watertight expansion joints over the piers and abutments in combination with proper
drainage serve to protect the piers, columns, and abutments from rain, snow, ice, and deicing salts.

37
In all structures, a reduction in concrete shrinkage will reduce the tendency for shrinkage crack-
ing (ACI Committee 224 2008). This can be achieved by using less water in the mix and the largest
practical maximum aggregate size. A lower water content can be achieved by using a well-graded
aggregate, stiffer consistency, and lower initial temperature.
ACI Committee 224 (2008) lists the following items to be included in specifications to minimize
drying shrinkage:
• Cement should be AASHTO M 85 Types I, II, V; AASHTO M 240 Types IS and IP; or
ASTM C845.
• Aggregates should be well-graded and well-shaped with minimum amounts of clay, dirt, and
excessive fines. Rock types that result in low shrinkage concrete should be used.
• The largest practical maximum coarse aggregate size and the lowest practical fine aggregate
size should be used.
• The lowest practical slump and concrete temperature should be used.
Internal Curing
Internal curing is defined by the ACI as “a process by which the hydration of cement continues because
of the availability of internal water that is not part of the mixing water” (ACI 2013). Internally cured
concrete uses absorptive materials in the mixture that supplement standard curing practices by supplying
moisture to the interior of the concrete. This process adds moisture without affecting the w/cm ratio. The
water addition can be achieved using a variety of materials (Kovler and Jensen 2007), but for bridges, the
most likely material is prewetted, lightweight aggregate. More information about the use of prewetted,
lightweight aggregate is provided in ACI Report (308-213)R-13 (ACI Committee 308 2013).
The use of prewetted, lightweight aggregate (LWA) can minimize the development of autogenous
shrinkage and help to avoid early-age cracking (Wei and Hansen 2008; Bentz and Weiss 2011). At
the same time, the use of prewetted LWA has been shown to increase hydration, decrease shrinkage
and permeability, and increase compressive strength.
The use of LWA for internal curing is described in ASTM C1761/C1761M (“Standard Specification
for Lightweight Aggregate for Internal Curing of Concrete”). An appendix provides guidance on cal-
culating the quantity of LWA for internal curing. There is also a guide on the website of the Expanded
Shale, Clay and Slate Institute (www.escsi.org). A procedure for mix proportioning has been reported
by Bentz et al. (2005). Internal curing has been used in bridges in Illinois (Tollway), Indiana, Iowa,
New York, Ohio, Texas, Utah, and Virginia.
In 2010, a pair of bridge decks was cast in Monroe County, Indiana (Weiss et al. 2013). Both
decks were cast using ready-mixed concrete. The first deck was cast using a conventional bridge
deck concrete, and the second was cast using an internally cured concrete made using the same raw
materials. Although the 1-day strength of the internally cured concrete was approximately 10% less
than that of the conventional concrete, the conventional and internally cured concrete had equivalent
strengths at approximately 10 days. After 3 months, the internally cured concrete was 20% stronger
than the conventional concrete. Tests per AASHTO T 277 showed that the internally cured concrete
had a 10% lower charge passed through at 28 days and nearly 40% lower charge passed through after
3 months. The internally cured mixture also had a lower shrinkage. Cracks developed in the conven-
tional concrete deck after the first few months of service, whereas the internally cured concrete had
no visible cracking at 1 year after placement.
New York State DOT has used internal curing on at least 17 bridges located throughout the state
(Streeter et al. 2012). The New York State DOT uses a special mixture design that is similar to their
conventional deck concrete mix design (nearly 650 lb/yd3 of cementitious material with silica fume)
but includes 200 lb/yd3 of fine LWA. According to Streeter et al. (2012), internal curing has been
shown to provide improvements by reducing the cracking associated with concrete shrinkage but
has not eliminated all deck cracking. It presented no problems to concrete suppliers when batching
concrete or to contractors placing and finishing concrete on the bridges.

38
According to Bentz and Weiss (2011), there were no negatives associated with using internal curing
on the New York State bridges; however, the potential benefits need to be quantified through com-
parisons with conventional concrete bridge deck materials. Three internally cured decks were walked
to assess their performance after 1 to 3 years, and only one small crack was observed in the negative
moment region of one internally cured bridge deck. Conversely, the parapet walls and sidewalks pro-
duced with concrete without internal curing showed several large cracks. The decks appeared to be
wearing as expected. The New York State DOT permits these concretes to be pumped, and no problems
have been reported (Bentz and Weiss 2011).
In Ohio, the DOT used a modified HPC No. 4 mixture that contained 595 lb/yd3 of cementitious mate-
rials and silica fume. Approximately 200 lb/yd3 of LWA was used for internal curing. The mixture was
pumped to the deck without incident and maintained sufficient entrained air. The mixture was reported
to have strengths that were similar or superior to the conventional mixture without internal curing.
In May 2007, two bridge decks were cast in Euclid, Ohio; one deck used a standard Ohio DOT
deck mixture, and one incorporated internal curing (Delatte and Crowl 2012). About 5 weeks after
the decks were cast, two small cracks were observed on the underside of the bridge below the side-
walk at points where two pieces of formwork came together. A second inspection 4½ years after
casting revealed no additional cracks on both decks.
The city of Cleveland has a major bridge across the Cuyahoga River, known as the Main Avenue
Bridge, with a deck constructed of LWA concrete with expansive cement. This deck was placed dur-
ing renovations in 1992. In 2011, the deck was still showing excellent performance with no cracks
visible on the top of the deck. The underside could not be inspected because stay-in-place metal
forms were used (Delatte and Crowl 2012).
Four CIP concrete bridge decks over precast concrete deck panels were built in Northern Utah:
two constructed with conventional concrete and two containing prewetted lightweight fine aggregate
(Guthrie and Yaede 2013; Bitnoff 2014). Data from sensors embedded in the CIP concrete decks
indicated that the moisture content of the internally cured concrete was 2% to 4% higher than the
moisture content of the conventional concrete for the first year after deck construction but less than
2% at 2 years. At 28 days, the average compressive strength of the internally cured concrete was 1%
higher than that of the conventional concrete, but at 1 year the conventional concrete was 13% stron-
ger. In rapid chloride permeability testing, the internally cured concrete consistently passed between
13% and 18% less current than did the conventional concrete.
In the field, rebound hammer testing showed similar concrete strengths for both deck types at 1 year
but showed that the internally cured concrete was weaker than the conventional concrete at 2 years. On
average, the internally cured concrete exhibited between 2% and 16% and between 12% and 46%
greater chloride concentration, depending on the depth interval, than did a conventional concrete at
1 and 2 years, respectively. After 2 months, three to five cracks 0.008 to 0.12 in. wide were found
on each of the conventional concrete bridge decks, but no visible signs of cracking were found in
the bridge decks with internal curing. At 5, 8, 12, and 24 months, the conventional concrete bridge
decks had 4.8, 6.6, 2.5, and 1.3 times more cracking, respectively, than did the internally cured con-
crete decks. During surveys at 1 and 2 years, distinctive reflective cracks from the joints between the
underlying precast, partial-depth deck panels were observed on all of the decks.
A laboratory testing program was conducted for the Florida DOT to evaluate the properties of
three standard concrete mixes and three corresponding internally cured concrete mixes with the same
w/cm ratios and the same cementitious materials contents (Tia et al. 2015). The average compressive
strength, flexural strength, modulus of elasticity, and splitting tensile strength of the internally cured
mixes were lower than were those of the corresponding standard mixes. The differences ranged from
10% to 18%. The average cracking age of all internally cured mixes, as measured by the restrained
shrinkage ring test, was 2.7 times that of the standard mixes.
Jones et al. (2014) investigated autogenous shrinkage, restrained shrinkage cracking, and free
shrinkage in a 50% relative humidity drying condition of internally cured concrete for use in Colo-

39
rado. Internally cured mixtures minimized autogenous shrinkage and caused initial expansion (or
swelling) in a sealed system. Restrained shrinkage showed that internally cured concrete reduced the
residual stress buildup in the material. Internally cured mixtures had less drying shrinkage because
water present in the matrix allowed continuous hydration as the surface dried.
A bibliography on internal curing is available at http://concrete.nist.gov/~bentz/phpct/database/

ic.html.
Self-Consolidating Concrete
Self-consolidating concrete (SCC) is defined as a highly flowable nonsegregating concrete that can
spread into place, fill the formwork, and encapsulate the reinforcement without any mechanical
consolidation (ACI Committee 237 2007). Its use is beneficial for casting complex shapes or mem-
bers with congested reinforcement. SCC is made with conventional concrete materials except that a
viscosity-modifying admixture may be included.
SCC has been used in the construction of many bridges including its use in drilled shafts, pile
caps, columns, precast bridge beams, precast deck panels, and connections between precast com-
ponents. It has also been used in the rehabilitation of existing bridges. Its use in CIP decks has been
limited because the concrete tends to flow downhill, making it difficult to cast sloping elements.
Some states restrict its use to certain bridges components.
SCC can be prone to plastic shrinkage cracking because the mixtures exhibit little or no surface
bleeding (ACI Committee 237 2007). Thus, it is important to protect the concrete from early mois-
ture loss (ACI Committee 237 2007). The increased paste volume in SCC creates a potential for
increased drying shrinkage (PCI 2015). However, drying shrinkage of SCC can be similar to or less
than that of conventional concrete.
NCHRP Report 628: Self-Consolidating Concrete for Precast, Prestressed Concrete Bridge
Elements provides guidelines for the use of SCC in precast, prestressed concrete bridge elements
(Khayat and Mitchell 2009). Tests on four full-scale AASHTO Type II girders indicated that the
greater shrinkage of SCC compared with that of HPC can lead to larger prestressing losses and
smaller camber. SCC and HPC girders of similar compressive strengths exhibit similar flexural
cracking moments and cracking shear strengths.
Kim et al. (2015) reported that the AASHTO expressions for estimating the cracking moment of
precast, prestressed concrete bridge girders were appropriate for a girder made with a river gravel
SCC but slightly overestimated the cracking moment for a girder made with a limestone SCC.
Summary of the Effects of Concrete Constituent Materials
The following materials and criteria have been identified as being beneficial in the reduction of
cracking in concrete bridge decks:
• Using a cement content not greater than 650 lb/yd3.

• Using SCMs.
• Using the largest maximum aggregate size and maximum aggregate content that can be prop-
erly placed.
• Using aggregates with an optimized combined aggregate gradation.
• Using an SRA.
• Using internal curing.
• Using a w/cm ratio in the range of 0.40 to 0.45.

40
chapter four
Effects of Construction Practices on Cracking
Curing Practices
Plastic shrinkage cracks occur in the top surface of concrete when job conditions are so dry that
moisture is removed from the surface at a faster rate than it is replaced by bleed water (ACI Com-
mittee 224 2008). The rate of evaporation depends on the air and concrete temperatures, air relative
humidity, and wind speed. If the rate of evaporation approaches 0.2 lb/ft2/h, precautions against
plastic shrinkage cracking are needed. The potential for plastic shrinkage cracking can be minimized
by not placing concrete when conditions are not favorable or taking precautionary methods such as
fog spraying. The National Ready Mixed Concrete Association nomogram is often used to determine
evaporation rates (ACI Committee 305 2014).
ACI 224R-01 states that the most effective curing environment is to keep the concrete continu-
ously wet with a wet cover in contact with the surface of the concrete for at least 7 days (ACI Com-
mittee 224 2008). At the end of the curing period, the cover is to be left in place until it and the
concrete surface appear dry. Shrinkage cracking in hardened concrete can occur shortly after the end
of water curing if the concrete is allowed to dry too rapidly. ACI 224R-01 also states that rapid dry-
ing can be prevented by using a curing compound after water curing. Wet curing of concrete bridge
decks is illustrated in Figures 14 and 15.
Based on the results from the survey for this synthesis, all responding agencies except one wet
cure concrete bridge decks. However, the duration of wet curing varies from 3 to 14 days, as shown
in Figure 16. Clearly, most states cure the deck concrete for 7 to 14 days. This is consistent with the
length of curing periods reported in a 2012 survey (Russell 2013). Most agencies wet cure the decks
using soaker hoses in combination with prewetted burlap and plastic sheeting, curing blankets, or
plastic-coated burlap.
In a survey for NCHRP Synthesis 333 published in 2004, agencies in the United States and
Canada indicated a range of curing periods from 3 to 14 days, the most frequent time period
being 7 days (Russell 2004). However, between 2004 and a survey in 2012, the percentage of
agencies specifying 7 days or fewer decreased from 87% to 67%, and the percentage specifying
14 days had increased from 11% to 24%. In the 2012 survey, only two states reported fewer than
7 days of wet curing.
Based on their experiences with cracking on the westbound Kernville viaduct, the Pennsylva-
nia DOT (PennDOT) adopted the following construction considerations for the eastbound bridge
(Spangler and Tikalsky 2006):
• Place positive moment regions on 1 day followed by the placement of negative moment regions
no less than 3 days later.
• Apply moist curing immediately after concrete finishing and maintain continuously for 10 days
with curing compound applied thereafter.
• Increase vigilance in quality control and quality assurance operations.
Based on a research study for the Indiana DOT, Frosch et al. (2002) recommended a minimum 7-day
wet curing process to reduce overall shrinkage strains and that the drying shrinkage of the concrete
mix should be minimized through concrete mix design and materials selection. Concrete compressive

41
FIGURE 14 Application of wet burlap within minutes of strike off

(Courtesy: Michigan DOT).
FIGURE 15 Application of polyethylene sheeting to ensure wet

curing (Courtesy: Texas DOT).
FIGURE 16 Duration of wet curing for concrete bridge decks.

42
strengths higher than specified by structural design are not required and can exacerbate deck cracking.
Higher concrete compressive strengths can require additional cementitious materials that produce con-
cretes with higher shrinkage, higher tensile strength, and higher modulus of elasticity. The higher ten-
sile strength is beneficial in reducing cracking, but its benefit is more than offset by the higher shrinkage
and higher modulus of elasticity, which contribute to higher tensile stresses.
Weather Conditions
Krauss and Rogalla (1996) identified that weather conditions, such as high temperatures and low
humidity, and inadequate curing are construction factors that affect deck cracking. They recommended
that concrete placement cease or protective measures be taken during periods of high evaporation.
Casting concrete decks at night significantly reduced deck cracking. They recommended wet curing
during hot weather and for a period of at least 14 days.
Kivisto (2003) reported two instances when construction practices led to cracking in bridge
decks. The first instance happened in 1999, when the specifications required the contractor only
to fog the deck to keep it wet below placing wet burlap. During the deck placement, the wind
speed increased, and the manual fogging operation was not able to keep up with the rate of evapo-
ration. As a result, several areas of map cracking were evident in the deck after completion of
the curing period. As a result, the specifications were revised to require placement of wet burlap
within 15 minutes of finishing and the burlap to be maintained in a wet condition for 7 days after
placement of the deck.
A second instance of deck cracking occurred in 2002, when the contractor did not have the work
bridges set up behind the paving machine for immediate application of the wet burlap. The contractor
tried to fog the deck from the ends and sides of the bridge. As the wind increased, the manual fogging
was not able to keep up with the surface evaporation. Transverse cracks at 5-ft intervals occurred
throughout the deck.
Placement Length and Construction Sequence
Construction sequence can influence transverse deck cracking in the negative moment regions of
continuous structures. If the negative moment region is cast before the positive moment region, the
casting of the positive moment region introduces tensile stresses in the top of the negative moment
region. The practice of casting the positive moment region ahead of the negative moment region is
aimed at alleviating this situation but may not always be practical.
Although placement sequences are specified in the bridge plans, contractors often employ their
own placing sequence (Schmitt and Darwin 1995). These new sequences should be approved by
the engineer, but frequently they are not recorded. Given the limited data available on the subject,
researchers have found varying levels of importance in placement sequence and its relationship
to cracking.
Perfetti et al. (1985) calculated the concrete stresses caused by the construction sequences of
16 continuous steel girder bridges built in North Carolina. They reported no consistent correlation
between the incidence of transverse deck cracking and the maximum tensile stresses induced by only
the dead load of the concrete. However, when the tensile stresses from live load were combined with
the residual dead load stresses, a correlation existed between the calculated tensile stresses and the
incidence of deck cracking. They recommended that alternate casting sequences be considered to
minimize tensile stresses.
Schmitt and Darwin (1995), in an investigation of 40 bridge decks in northeast Kansas, could not
identify any relationship between cracking and placement length for monolithic bridge decks. How-
ever, cracking clearly increased as placement length increased for bridge deck overlays. Krauss and
Rogalla (1996) reported that placement sequence is important but that the sequence is not a primary
cause of transverse deck cracking.

43
Babaie and Fouladgar (1997) pointed out that flexural transverse cracks over supports of continu-
ous structures can be lessened by placing concrete in the center portion of adjacent spans before
placing the concrete over the supports.
Ramey et al. (1997) recommend a detailed placing procedure as follows:
• Place complete deck at one time when possible.

• Place simple span bridges one span per placement, or if span is long, divide the deck longitu-
dinally and place each strip at one time. If this cannot be done, place the center of the span first
and then place other portions.
• If multiple placements are made on continuous beams, place middle spans first and wait 72 hours
between placements. Use a bonding agent to enhance bond at construction joints.
According to Saadeghvaziri and Hadidi (2002), earlier studies (Cheng and Johnston, 1985; Per-
fetti et al. 1985) reported that placement length and sequence do not appear to influence crack-
ing. However, later studies suggested that placement length, sequence, and rate of placement may
have some effects on deck cracking, and Saadeghvaziri and Hadidi (2002) recommended placement
sequences similar to those suggested by Ramey et al. (1997) and that the placement sequence be
specified.
Kochanski et al. (1990) recommend placing concrete at a rate faster than 0.6 span lengths per
hour. In an analytical study, Issa (1999) attributed cracking to sequence of placement and recom-
mended placing concrete in positive moment regions first. Hopper et al. (2015) made the same
recommendation.
The Uphapee Creek Bridge in Alabama consists of seven equal simple spans of 114 ft (Mokarem
et al. 2009). Almost 100% of the cracks in the bridge deck occurred in the transverse direction and
were located in the quarter-span lengths at the end of each span. The middle half of each span was
relatively free of cracks. The center portion of each span was cast first and the quarter lengths were
cast several days later. The measured properties of the concrete used in the quarter and center lengths
were similar. The casting of the quarter lengths after the center would induce compressive stresses
in the deck of the center portion and may explain why the center portion was relatively crack free.
Other Practices
Frosch et al. (2002) also suggested that alternatives to stay-in-place metal deck forms should be con-
sidered because the pan shape causes stress concentrations and the pan prevents inspection of the
underside of the deck. The use of a metal angle with a leg upturned into the deck should be discontinued
because the leg produces a crack initiator along the edge of the girders’ top flanges.
Summary of Construction Practices
Construction practices that can reduce the likelihood of deck cracking include the following:
• Applying wet curing procedures immediately after concrete finishing and maintaining the surface
wet for at least 7 days.
• Applying a curing compound after the wet curing period.
• Where practical, using a placement sequence minimizes tensile stresses in previously placed
fresh concrete.
• In hot or low humidity conditions, placing concrete at night.

44
chapter five
Effects of Reinforcement Type on Crack Control
Yield Strength of Reinforcement
It is generally accepted that crack widths in nonprestressed concrete members increase as the tensile
stress in the reinforcement increases. Consequently, the use of higher strength reinforcement will lead
to wider crack widths unless an upper limit is placed on the tensile stress in the reinforcement under
service loads. Some agencies have chosen to do this. In doing so, the advantage of the higher strength
reinforcement is reduced.
Sharooz et al. (2011) collected extensive data on crack widths during flexural tests of concrete beams
reinforced with ASTM A1035 Grade 100 reinforcement. They concluded that, at service load levels as
great as a steel stress level of 72 ksi, average crack widths were less than the limits of 0.017 and 0.013 in.
that are assumed for Class 1 and 2 exposure conditions, respectively, in Article 5.6.7 (formerly 5.7.3.4)
of the AASHTO LRFD Specifications. When the AASHTO LRFD Specifications were revised to
permit the use of reinforcement with a specified yield strength, fy, to 100 ksi, the calculated stress in
nonprestressed reinforcement at the service limit state was limited to 0.60fy (AASHTO 2013).
Corrosion-Resistant Steel Reinforcement
In the survey for this synthesis, agencies identified the types of corrosion-resistant steel reinforcement
used in CIP concrete bridge decks. The results are shown in Table 6.
Clearly, epoxy-coated reinforcement remains the predominant type of corrosion-resistant reinforce-

ment used in bridge decks. All agencies that reported the use of epoxy-coated reinforcement in bridge
decks reported using it in both layers of reinforcement. Agencies also reported the use of zinc coating,
stainless steel coating, and solid stainless steel reinforcement and that their use did not affect deck
cracking. The use of ASTM A1035 reinforcement is relatively new, and no information was reported
about its effect on deck cracking.
Tension tests of reinforced concrete prisms by Patnaik and Baah (2015) revealed that the concrete
specimens with epoxy-coated bars developed a first crack at smaller loads and developed larger crack
widths that did corresponding specimens with uncoated bars. Flexural tests of reinforced concrete
slabs with epoxy-coated bars showed a first crack at smaller loads, wider cracks and a larger number
of cracks, and failure at smaller loads than was seen in the corresponding test specimens with uncoated
bars. To investigate a preventive measure, slab specimens with basalt MiniBar or polypropylene fibers
were included in the test program. These specimens exhibited higher cracking loads, smaller crack
widths, smaller midspan deflections, and higher failure loads than those seen with the slab specimens
without fibers. The authors concluded that merely satisfying the reinforcement spacing requirements
given in the AASHTO LRFD Specifications was not adequate to limit cracking below the maximum
limits recommended by ACI 224R-01 (ACI Committee 224 2008), even though all the relevant design
requirements were otherwise met.
Hart and Lysogorski (2005) reported on 27 state projects that had used corrosion-resistant reinforce-
ment under the FHWA Innovative Bridge Research and Construction Program. The different reinforce-
ment types included solid stainless steel Types 316, 2201LDX, and 2205; stainless Type 316 clad bars;
low-carbon chromium steel bars; and galvanized steel bars. The various state projects demonstrated

45
Table 6
Use of Corrosion-Resistant Reinforcement
Respondents
Type of Reinforcement Number Percentage
Epoxy-coated in top layer 33 87
Epoxy-coated in bottom layer 33 87
Epoxy-coated in both layers 33 87
Epoxy-coated reinforcement projecting 23 64
into the deck from the beam
Zinc-coated 19 45
Stainless-steel–coated 13 13
Solid stainless steel 18 43
ASTM A1035 at 100 ksi 3 7
Other (type not listed) 3 3
that corrosion-resistant reinforcing bars can be used in bridge construction with relative ease. No
information about the effect on cracking was reported.
Salomon and Moen (2014) showed, by testing and analysis, that slab specimens reinforced with
ASTM A1035 or UNS S32304 steel bars had similar deformability ratios and crack widths that com-
plied with current AASHTO requirements, with as much as 36% less reinforcing steel compared with
Grade 60 reinforcement. Bridge deck slabs employing high-strength reinforcement without a defined
yield plateau provided ductility consistent with AASHTO ductility limits at a strength limit state.
Sim (2014) tested twelve 8-in.-thick slabs reinforced with conventional uncoated bars and six dif-
ferent corrosion-resistant bars to evaluate the influence of various materials on cracking. The bar types
affected the spacing and width of primary cracks. For the control of crack widths, the author recom-
mended that crack widths be calculated based on conventional bars and multiplied by modification
factors. These factors could also be used to reduce the bar spacings calculated for conventional bars.
Fiber-Reinforced Polymer Reinforcement
Fiber-reinforced polymer (FRP) reinforcement consists of a continuous fiber, such as glass, carbon, or
aramid, embedded in a resin matrix, such as epoxy, polyester, vinylester, or phenolics (ACI Committee
440 2007). The advantages of this type of reinforcement are that it does not corrode as does uncoated
steel reinforcement and is lighter to ship and install than is steel reinforcement. The first bridge built
in the United States using FRP reinforcement in the concrete deck was in West Virginia in 1996. The
bridge used glass FRP bars as deck reinforcement (Thippeswamy et al. 1998). Subsequently several
other agencies used FRP in bridge decks on an experimental basis, including ones in Kentucky (Trejo
et al. 2000), Michigan (Trejo et al. 2000), New Hampshire (Goodspeed et al. 2002), Ohio (Eitel and
Huckelbridge 2002; Huckelbridge and Eitel 2003), Texas (Bradberry and Wallace 2003), Vermont
(Benmokrane et al. 2006), Manitoba (Rizkalla et al. 1998), Québec (Tadros 2000; Benmokrane et al.
1999), and Calgary (Tadros 2000).
As part of the survey for this synthesis, 17 of 42 agencies responding identified that they had used FRP
reinforcement in CIP concrete bridge decks. Three agencies reported that its use was beneficial in reduc-
ing cracking. Other agencies did not respond to the question or did not know if FRP had been used. The
amount of FRP reinforcement often is based on control of crack widths, as discussed later in this chapter.
Nawy and Neuwerth (1977) reported that beams reinforced with FRP reinforcement had more
cracks than corresponding beams with steel reinforcement. The large number of well-distributed cracks
in the FRP-reinforced beams indicated that good mechanical bond was developed between the FRP bar
and surrounding concrete.
Faza and GangaRao (1992) determined that concrete beams reinforced with spirally deformed
FRP-reinforcing bars in 4.0-ksi compressive strength concrete exhibited crack formation that was

46
sudden and propagated toward the compression zone as soon as the concrete stress reached its ten-
sile strength. Crack spacing was determined by the stirrup spacing. With higher strength concrete
and sand-coated FRP reinforcing bars, the propagation of cracks and crack widths decreased. An
expression for maximum crack spacing was developed.
In 2000, the Texas DOT used glass fiber-reinforced polymer (GFRP) bars as the top mat of rein-
forcement in the CIP topping on partial-depth, precast, prestressed concrete panels on the Sierrita
de la Cruz Creek Bridge near Amarillo (Bradberry and Wallace 2003). The design was governed
by serviceability considerations with the estimated crack width being the controlling parameter.
The designer chose the maximum crack width of 0.02 in. recommended by the Canadian Standards
Association (CSA 1996). The calculated maximum stress for this crack width for this slab was less
than 15% of the guaranteed ultimate strength of the bar. This resulted in No. 6 GFRP bars with cen-
ters spaced at 5½ in. With epoxy-coated reinforcement, No. 5 bars at 6-in. spacing would have been
required. Thus, the use of GFRP bars required 42% more area of reinforcement and 7% closer
bar spacing compared with the use of epoxy-coated reinforcement (Bradberry 2001).
In 2015, nine concrete cores were extracted from different locations on the bridge for various analy-
ses (Gooranorimi et al. 2016). Carbonation depth and pH of the concrete surrounding the GFRP bars
were measured. Scanning electron microscopy imaging and energy dispersive X-ray spectroscopy were
performed to monitor any microstructural degradation or change in the GFRP chemical compositions.
Finally, GFRP interlaminar (horizontal) shear strength, glass transition temperature, and fiber content
were determined and compared with the results of similar tests performed on control samples at the time
of construction. Microscopic examination revealed no GFRP degradation. Fibers did not lose any cross-
sectional area, the matrix was intact, and no damage was observed at the fiber-matrix interface. In addi-
tion, the concrete-GFRP interface was maintained properly, and no interfacial bond loss was observed.
Soroushian et al. (2001) caution that the substitution of FRP reinforcement for steel reinforcement
on an equal area basis typically results in significantly higher deflections with wider crack widths. In
addition, shear capacity is likely to be significantly reduced as a result of increased crack widths and
reduced size of the compressive stress blocks.
In Virginia, the deck of one end span of the Gills Creek Bridge was constructed with GFRP bars
as the top mat and epoxy-coated steel bars as the bottom mat (Phillips et al. 2005). Live load
tests were performed in 2003, shortly after completion of construction, and again in 2004. In
addition, tests were performed on the deck of the opposite end span, which had all epoxy-coated
steel reinforcement. There were no significant differences in the behavior of the deck after 1 year of
service, and there was no visible cracking. The behavior of the two end spans was similar, and the mea-
sured girder distribution factors were less than the AASHTO design recommendations. The impact
factors were less-than-design values for the 2003 tests but higher-than-design values for the 2004
tests. Stresses in the GFRP-reinforcing bars were much less than the design allowable stress and did
not change significantly after 1 year of service.
In 2013, the Kansas DOT replaced the decks of the I-635 bridges over State Avenue in Kansas City
with traditional epoxy-coated steel reinforcement in the northbound bridge and GFRP reinforcement in
the southbound bridge (Koch and Karst 2015). The deck with the epoxy-coated steel reinforcement con-
tained No. 5 bars at 6-in. centers, whereas No. 6 bars at 6-in. centers were used in the GFRP-reinforced
deck. There was a small premium to use GFRP reinforcement over traditional steel reinforcement. This
is expected to be offset by an increase in the service life of the deck.
ACI Committee 440: Fiber-Reinforced Polymer Reinforcement recommends the use of the
Canadian Standards Association’s limits for crack widths with FRP reinforcement (ACI Commit-
tee 440 2006). The Canadian standard (CSA 2002) implicitly allows crack widths of 0.020 in. for
exterior exposure. However, Committee 440 cautions that the limit may not be sufficiently restric-
tive for structures exposed to aggressive environments.
Committee 440 also proposes that a modified version of the Frosch equation (Frosch 1999) be
used to calculate maximum probable crack width:

47
()
2
ff s
wcu = 2 β s k b ( d c )2 + (3)
Ef 2
where
wcu = maximum probable crack width for FRP reinforcement (in.);

ff = stress in FRP reinforcement (ksi);
Ef = modulus of elasticity of FRP reinforcing bars (ksi);
βs = ratio of distance between the neutral axis and tension face to the distance between the neutral
axis and the centroid of the reinforcement;
kb = bond quality coefficient;
dc = thickness of concrete cover measured from extreme tension fiber to center of the flexural
reinforcement located closest thereto (in.); and
s = spacing of nonprestressed reinforcement in the layer closest to the tension face (in.).
Analysis of available data indicated that kb could vary from 0.60 to 1.72, depending on the surface char-
acteristics of the bar. A value of 1.4 was recommended in instances in which the actual value is unknown.
A design example for a beam illustrates that crack width criteria control the amount of FRP reinforce-
ment (ACI Committee 440 2006). The use of the Frosch equation with steel reinforcement is discussed
in the next chapter.
Although the highly alkaline environment of concrete is beneficial in preventing corrosion of

conventional uncoated steel reinforcement, its effect on FRP reinforcement may be detrimental (ACI
Committee 440 2007). Tests have shown that FRP bars placed in a highly alkaline solution can lose
tensile strength (Mehus 1995; ElSafty et al. 2014). Thus, it is important that FRP bars be evaluated
for alkali resistance.
Specifications for Crack Control
This section of the synthesis contains a summary of the articles in the AASHTO LRFD Bridge Design
Specifications (AASHTO 2017) that relate to the use of reinforcement to control cracking when it
occurs. Some background to the articles and information about relevant research is also provided. Some
of these articles originally were developed for Grade 60 steel reinforcement, and their appropriateness
for use in crack control with higher strength reinforcement, corrosion-resistant reinforcement, and FRP
reinforcement may not have been verified.
Article 5.6.3.3: Minimum Reinforcement
Article 5.6.3.3 (formerly 5.7.3.3.2) contains provisions for minimum reinforcement intended to reduce
the probability of brittle failure by providing a flexural capacity greater than the cracking moment
of the member. Unless otherwise specified, at any section of a noncompression-controlled flexural
component, the amount of prestressed and nonprestressed tensile reinforcement shall be adequate to
develop a factored flexural resistance, Mcr, greater than or equal to the lesser of the following:
• 1.33 times the factored moment required by the applicable strength load combination specified
in Table 3.4.1-1;
 ( Snc )
• Mcr = g 3 ( g 1 fr + g 2 fcpe ) Sc − M dnc Sc − 1 

( 5.6.3.3-1) (4)
where
Mcr = cracking moment (kip-in.);

fr = modulus of rupture of concrete specified in Article 5.4.2.6 (ksi);

48
fcpe = compressive stress in concrete caused by effective prestress forces only (after allowance
for all prestress losses) at extreme fiber of section where tensile stress is caused by exter-
nally applied loads (ksi);
Mdnc = total unfactored dead load moment acting on the monolithic or noncomposite section
(kip-in.);
Sc = section modulus for the extreme fiber of the composite section where tensile stress is
caused by externally applied loads (in.3);
Snc = section modulus for the extreme fiber of the monolithic or noncomposite section
where tensile stress is caused by externally applied loads (in.3);
g1 = flexural cracking variability factor;
g2 = prestress variability factor; and
g3 = ratio of specified minimum yield strength to ultimate tensile strength of the nonpre-
stressed reinforcement.
Equation 5.6.3.3-1 was developed by Holombo and Tadros (2009) to provide a rational design pro-
cedure for minimum reinforcement to prevent brittle failure of concrete sections. This was achieved
through the use of the gamma factors. A subsequent NCHRP Project 12-94 is investigating minimum
flexural reinforcement requirements.
Article 5.6.7 (Formerly 5.7.3.4): Control of Cracking by Distribution of Reinforcement
Article 5.6.7 addresses the distribution of tension reinforcement to control flexural cracking for
all concrete components, except deck slabs designed in accordance with Article 9.7.2: Empirical
Design. The article requires that the spacing, s, of nonprestressed reinforcement in the layer closest
to the tension face shall satisfy the following equation:
700 g e
s≤ − 2d c ( 5.6.7-1) (5)
β s fss
in which
dc
βs = 1 + ( 5.6.7-2 ) (6)
0.7 ( h − dc )
where
bs = ratio of flexural strain at the extreme tension face to the strain at the centroid of the reinforce-
ment layer nearest the tension face;
ge = exposure factor;
= 1.00 for Class 1 exposure condition;
= 0.75 for Class 2 exposure condition;
reinforcement located closest thereto (in.);
fss = calculated tensile stress in steel reinforcement at the service limit state not to exceed
0.60 fy (ksi); and
h = overall thickness or depth of the component (in.).
Class 1 exposure condition relates to an estimated maximum crack width of 0.017 in., and
Class 2 relates to an estimated maximum crack width of 0.013 in. Class 2 typically is used for situa-
tions in which the concrete is subjected to severe corrosion conditions, such as bridge decks exposed
to deicing salts and substructures exposed to water. Class 1 is used for less corrosive conditions and
could be thought of as an upper bound in regard to crack width for appearance and corrosion (SHRP 2
2015). The different classes of exposure conditions have been so defined in the design specifications
to provide flexibility in the application of these provisions to meet the needs of the bridge owner. A
calibration study of Equation 5.6.7-1 determined that the reliability indices for a 1-year return period
and 5,000 average daily truck traffic were 1.6 and 1.0 for Class 1 and Class 2 exposure conditions,
respectively (SHRP 2 2015).

49
The intent of the article is to control flexural cracking in which the crack width is assumed to be pro-
portional to its distance from the neutral axis as represented by bs. However, most cracks in the bridge
decks are caused by restrained shrinkage, differential temperatures, or discontinuities in the supporting
beams or slabs. The cracks are usually full depth and have a width somewhat constant. Therefore, the
use of the article to control some types of cracking in bridge decks may not be appropriate.
As part of the survey for this synthesis, the states were asked whether they used Article 5.6.7 of
the AASHTO LRFD Specifications to determine maximum spacing of reinforcement in bridge decks.
Responses were as follows:
• Yes, with no modifications: 26 U.S. agencies;

• Yes, with modifications: eight U.S. agencies; and
• No: four U.S. agencies.
Most agencies reported using an exposure factor of 1.0, with 12 agencies reporting a value of 0.75
for some or all applications. The agencies also listed the following modifications related to Article 5.6.7:
• Decks made continuous (link slabs) have supplemental reinforcement.

• AASHTO LRFD Specifications were used before the 2005 Interim revisions.
• Maximum value for cover used to calculate dc was 2 in., whereas actual cover was 3 in.
• Quantity of reinforcement was checked against the Frosch et al. (2002) equation.
• Standardized deck designs were used. Article 5.6.7 was rarely used.
• Concrete compressive stress was limited at the service limit state because of the positive bend-
ing moment between girders to 0.4 f c′, bar spacing to 8 in. maximum, and reinforcement bar size
in decks to No. 6 maximum.
• The definition of dc was modified and defined where Class 1 and Class 2 apply.
• Redistribution percentage was modified in terms of c/de ratio.
Article 5.7.2.5 (Formerly 5.8.2.5): Minimum Transverse Reinforcement
Where transverse reinforcement is required and nonprestressed reinforcement is used to satisfy that
requirement, the area of steel shall satisfy:
 b s
Av ≥ 0.0316l f c′  v  ( 5.7.2.5-1) (7)
 fy 
where
Av = area of transverse reinforcement within distance s (in.2);

bv = width of web adjusted for the presence of ducts as specified in Article 5.7.2.8 (in.);
s = spacing of transverse reinforcement (in.);
fy = yield strength of transverse reinforcement (ksi) ≤ 100 ksi; and
l = concrete density modification factor, as specified in Article 5.4.2.8.
A minimum amount of transverse reinforcement is required to restrain the growth of diagonal shear
cracks and ensure that the member has adequate ductility.
Article 5.7.2.6 (Formerly 5.8.2.7): Maximum Spacing of Transverse Reinforcement
Article 5.7.2.6 specifies a maximum spacing of transverse reinforcement to ensure that any diagonal
crack is intersected by a reinforcing bar. The spacing of the transverse reinforcement shall not exceed
the maximum permitted spacing, smax, determined as:
• If vu < 0.125 f c′, then:
smax = 0.8d v ≤ 24.0 in. ( 5.7.2.6-1) (8)

50
• If vu ≥ 0.125 f c′, then:
smax = 0.4 d v ≤ 12.0 in. ( 5.7.2.6-2 ) (9)
where
vu = shear stress calculated in accordance with Article 5.7.2.8 (ksi); and

dv = effective shear depth as defined in Article 5.7.2.8 (in.).
Article 5.8.2.6 (Formerly 5.6.3.6): Crack Control Reinforcement
For members designed using the strut-and-tie method, Article 5.8.2.6 requires the use of orthogonal
grids of bonded reinforcement in structures and components or regions thereof, except for slabs and
footings, to control the width of cracks and ensure a minimum ductility for the member so that, if
required, significant redistribution of internal stresses is possible.
The spacing of the bars in these grids shall not exceed the smaller of d/4 and 12.0 in. The rein-
forcement in the vertical direction shall satisfy the following:
Av
≥ 0.003 ( 5.8.2.6-1) (10)
bw sv
and the reinforcement in the horizontal direction shall satisfy the following:
Ah
≥ 0.003 ( 5.8.2.6-2 ) (11)
bw sh
where
Ah = total area of horizontal crack control reinforcement within spacing sh (in.2);

Av = total area of vertical crack control reinforcement within spacing sv (in.2);
bw = width of member’s web (in.); and
sv, sh = spacing of vertical and horizontal crack control reinforcement, respectively (in.).
Where provided, crack control reinforcement shall be distributed evenly near the side faces of the
strut. The required minimum reinforcement is based on the work of Birrcher et al. (2009) and Larson
et al. (2013).
Article 5.9.4.4.1 (Formerly 5.10.10.1): Splitting Resistance
Article 5.9.4.4.1 requires a minimum amount of splitting resistance in the webs of I-beams or webs
and bottom flanges of boxes and U-girders to control end region splitting cracks that may develop
parallel to the strands. The minimum amount of reinforcement is calculated as:
Pr
As = (12)
fs
where
As = total area of reinforcement located within the distance h/4 from the end of the beam (in.2);
Pr = splitting resistance taken as not less than 4% of the total prestressing force before transfer
(kip);
fs = stress in steel not to exceed 20.0 ksi (ksi); and
h = overall dimension of precast member in the direction in which splitting resistance is being
evaluated (in.).

51
For pretensioned I-girders or bulb tees, h is the overall height of the member. For pretensioned
solid or voided slabs, h is the overall width of the member. For pretensioned box or tub girders, h is
the lesser of the overall width or height of the member.
As part of the survey for this synthesis, the U.S. state agencies were asked whether they used Arti-
cle 5.9.4.4.1 to design splitting reinforcement at the ends of prestressed concrete beams. Responses
were as follows:

• Yes, with modifications: five U.S. agencies; and
• No: seven U.S. agencies
Modifications included the following:
• Use a minimum spacing of 10 in. for a distance of h/4.

• Provide the reinforcement over a distance greater than h/4 to facilitate concrete placement.
• Provide additional reinforcement to keep crack widths less than 0.012 in.
• Use a maximum spacing of 3 in.
• Consider end blocks when prestressing forces exceed 1,800 kip.
• Anchor closely spaced grids for members with prestressing forces in excess of 1,800 kip.
• Spread bars beyond h/4.
Based on NCHRP Project 18-14, Tadros et al. (2010) recommended that at least 50% of the split-
ting reinforcement be placed in the end h/8 of the member. The balance of the splitting reinforcement
was recommended to be placed in the distance between h/8 and h/2 from the member end. The reason
for this distribution was to concentrate the reinforcement at the location where the highest bursting
stresses are expected to exist.
Article 5.9.4.4.2 (Formerly 5.10.10.2): Confinement Reinforcement
Article 5.9.4.4.2 requires that reinforcement be placed to confine the prestressing steel in the bottom
flange of beams other than box beams for a distance of 1.5d from the end of the beam. The reinforce-
ment shall not be less than No. 3 deformed bars, with a spacing not exceeding 6 in. and shaped to
enclose the strands. For box beams, the transverse reinforcement must be provided and anchored by
extending the legs of stirrups into the webs of the beam.
As part of the survey for this synthesis, the states were asked whether they used Article 5.9.4.4.2 to
design confinement reinforcement at the ends of prestressed concrete beams. Responses were as follows:

• Yes, with modifications: three U.S. agencies; and
• No: three U.S. agencies.
Modifications included the following:
• Use closer spacing at beam ends but do not always extend the confinement reinforcement to
the full 1.5d.
• Use closer spacing at beam ends and extend the confinement reinforcement for the full length
of the beam using a wider spacing.
• Extend the confinement to 1⁄3 of the span with No. 4 bars at a spacing to match the vertical stirrup
spacing with a maximum spacing of 21 in.
Article 5.10.3.2 (Formerly 5.10.3.2): Maximum Spacing of Reinforcing Bars
Article 5.10.3.2 limits the maximum spacing of reinforcement in walls and slabs to 1.5 times the
thickness of the member or 18.0 in., whichever is the lesser.

52
Article 5.10.6 (Formerly 5.10.8): Shrinkage and Temperature Reinforcement
Article 5.10.6 contains requirements for minimum amounts of reinforcement at each face to control
shrinkage and temperature stresses in members exposed to daily temperature changes and in struc-
tural mass concrete. For bars or welded wire reinforcement, the area of reinforcement per foot on
each face and in each direction shall satisfy:
1.30 bh
As ≥ ( 5.10.6-1) (13)
( b + h ) fy
Except that
0.11 ≤ As ≤ 0.60 ( 5.10.6-2 ) (14)
where
As = area of reinforcement in each direction and each face (in.2/ft);

b = least width of component section (in.);
h = least thickness of component section (in.); and
fy = specified yield strength of reinforcing bars ≤ 75 ksi.
The coefficient of 1.3 in Equation 5.10.6-1 is the product of 0.0018, 60 ksi, and 12 in./ft. The equa-
tion is written to show that the total required reinforcement is distributed uniformly around the
perimeter of the component.
Article 5.12.2.3.3d (Formerly 5.14.4.3.3d): Longitudinal Construction Joints
Article 5.12.2.3.3d addresses longitudinal construction joints between precast concrete flexural
components. The joint shall consist of a keyway filled with a nonshrinkage mortar attaining a
compressive strength of 5.0 ksi within 24 hours. The depth of the keyway should not be less than
5.0 in. If the components are posttensioned together transversely, the amount of transverse pre-
stress, after all losses, shall not be less than 0.25 ksi through the keyway. In the last 3.0 ft at a
free end, the required transverse prestress shall be doubled. A similar article does not exist for
concrete decks on concrete beams.
Article 6.10.1.7: Minimum Negative Flexure Concrete Deck Reinforcement
Article 6.10.1.7 is applicable to CIP concrete decks on steel beams. It requires that an area of longi-
tudinal reinforcement not less than 1% of the total cross-sectional area of the concrete deck be pro-
vided where the longitudinal tensile stress in concrete exceeds the factored modulus of rupture of the
concrete. Article 6.10.3.2.4 requires that this check be made for various loading conditions, including
critical stages of construction. This article is intended to control cracking. A similar provision is not
provided for CIP decks on concrete beams.
Article 9.7.2: Empirical Design and Article 9.7.3: Traditional Design
Two methods for concrete bridge deck design are provided in Section 9 of the AASHTO LRFD
Bridge Design Specifications. The empirical method of Article 9.7.2 is based on the concept that the
primary structural action is by internal arching. It is applicable when certain design conditions apply
and requires that four layers of reinforcement be provided. The minimum amount of reinforcement
is 0.27 in.2/ft for each bottom layer and 0.18 in.2/ft for each top layer. Checking of bar spacing to
control flexural crack widths per Article 5.6.7 (formerly 5.7.3.4) is not required. Some states use the
concept of the empirical method but not exactly as stated in the AASHTO Specifications.
The traditional method of Article 9.7.3 is based on the assumption that the primary action is
flexural. Four layers of reinforcement are required, with distribution reinforcement provided in the

53
direction perpendicular to the primary reinforcement at a percentage of the amount of primary

reinforcement. Checking of bar spacing to control flexural crack widths per Article 5.6.7 (formerly
5.7.3.4) is required.
Conclusions about the Effects of Reinforcement Type on Crack Control
Various types of corrosion-resistant steel reinforcement have been used in bridges. The predominant
type continues to be epoxy-coated reinforcement. Zinc-coated, stainless-steel–coated, and solid stain-
less steel reinforcement have been used. Agencies reported that the use of these materials did not affect
deck cracking, although limited research shows opposite findings. Fiber-reinforced polymer reinforce-
ment has been used as nonprestressed reinforcement in CIP concrete bridge decks. In this application,
the amount of FRP reinforcement often is based on control of crack widths.
The AASHTO LRFD Bridge Design Specifications contain numerous articles about providing mini-
mum reinforcement to ensure minimum sectional strength if cracks occur. These articles also ensure
that crack widths will be controlled after a crack occurs. Narrower crack widths result from using
smaller diameter bars at a closer spacing. However, some agencies modify their design practices to
supplement some of the AASHTO LRFD Specifications. The LRFD articles do not encompass the full
range of reinforcement types available today.

54
chapter six
Influence of Cracking on Long-Term

Bridge Performance
One of the intents of providing concrete cover to steel reinforcement is to protect the reinforcement
from direct contact with materials that will cause corrosion, such as saltwater and deicing chemicals.
If cracks occur, that protection is lost, and this is the concern that owners have, particularly for bridge
decks and substructures. However, the following factors determine if corrosion actually occurs:
• Is the concrete surface exposed to chemicals that will cause the reinforcement to deteriorate?
• Can the chemicals reach the reinforcement?
• If the chemicals reach the reinforcement, will they cause deterioration?
If a crack is present and exposed to harmful chemicals, the chemicals will reach the level of the
reinforcement much earlier than if a crack is not present. Miller and Darwin (2000) reported signifi-
cantly higher chloride contents at the locations of cracks at the level of the transverse reinforcement.
The chloride contents exceeded the threshold level of corrosion in as little as 1,000 days. Lindquist
et al. (2005) reported that chloride concentrations taken at the level of the top transverse reinforce-
ment at crack locations can exceed the corrosion threshold in as little as 9 months and most bridge
decks exceeded the threshold level in 24 months. In contrast, the chloride levels away from the cracks
rarely exceeded even the most conservative estimates of the corrosion threshold for conventional
reinforcement.
According to ACI Committee 222 (2001), the role of cracks in the corrosion of reinforcing steel is
a matter of controversy. One viewpoint is that cracks permit deeper and rapid penetration of carbon-
ation, chloride ions, moisture, and oxygen. The other viewpoint is that chloride ions eventually pen-
etrate uncracked concrete, and the resulting corrosion of the reinforcement is more widespread. So,
after a few years, there is little difference between the amount of corrosion in cracked and uncracked
concrete. However, with the lower-permeability concrete being used today, the length of time for
chlorides to penetrate uncracked concrete is greater.
Cracks perpendicular to reinforcing bars hasten corrosion of the reinforcement at the crack location
by facilitating the ingress of moisture, oxygen, and chloride ions (Russell 2004). Studies have shown
that crack widths of less than 0.01 in. have little effect on the overall corrosion of the reinforcing steel
(Houston et al. 1972; Ryell and Richardson 1972). Although wider cracks may accelerate the onset
of corrosion over several years, crack width has little effect on the rate of corrosion (Beeby 1983).
Cracks that follow the line of a reinforcing bar are more serious because the length of the bar
exposed to the ingress of moisture, oxygen, and chlorides is equal to the length of the crack. This crack-
ing can initiate as settlement cracking, or the bars can create a weakened plane. In addition, the presence
of the cracks reduces the resistance of the concrete to spalling if the reinforcement corrodes.
Beeby (1983) reported that no consensus exists regarding the levels of cover, concrete quality,
and permissible crack width that should be specified. Beeby concluded that crack widths have little
influence on corrosion, and many design recommendations require unnecessary detailed calculations
for crack control as a corrosion control method.
Fanous et al. (2000) collected concrete cores from cracked and uncracked areas of bridge decks in
Iowa to determine the extent to which the epoxy-coated reinforcement had deteriorated at the location

55
of cracks and evaluate the impact of cracking on service life. No delaminations or spalls were found
in bridge decks constructed with epoxy-coated reinforcement. The oldest bridge deck was 20 years
old. All of the reinforcing bars extracted from uncracked locations showed no evidence of corrosion.
Most of the corrosion on the epoxy-coated bars was on bars extracted at cracked locations. For a
corrosion threshold range of 3.6 to 7.2 lb/yd3 for epoxy-coated reinforcement, the predicted service
life for Iowa bridge decks with epoxy-coated reinforcement was more than 50 years.
Rodriguez and Hooton (2003) investigated the influence of crack widths and crack surface rough-
ness on chloride ingress into concrete. Smooth and rough crack surfaces with widths ranging from
0.003 to 0.027 in. were exposed to a chloride bulk diffusion test. They concluded that chloride diffu-
sion was independent of crack width or crack wall roughness. The cracks behaved like free concrete
surfaces, greatly contributing to lateral chloride diffusion.
In Pennsylvania, concrete cores were extracted from 19 bridge decks and evaluated in the labora-
tory to determine the chloride content at the reinforcement level (Manafpour et al. 2016). For each
deck, an attempt was made to take one core sample at a crack location and one core off a crack
location. The chloride content at the reinforcement level for the on-crack locations was found to be
as much as 10 times greater than that for the samples from the off-crack locations in the same deck.
The chloride content was used to calculate the deck’s effective diffusion coefficient according to the
Fick’s second law, accounting for age and surface concentration of chlorides. On-crack effective dif-
fusion coefficients typically were as much as four times greater than off-crack values.
Brown et al. (2003) investigated the size and length of cracks in Virginia bridge decks to assess
the frequency and severity of the cracks. Correlation of cracks with chloride penetration was used to
characterize the influence of cracking on deck deterioration. Cracks influenced the rate of chloride
penetration, but the frequency and width distributions of cracks indicated that cracks are not likely
to shorten the overall service life of most bridge decks in Virginia.
It is reasonably well established that a chloride content of approximately 1.0 to 1.5 lb/yd3 at the
level of the reinforcement will initiate corrosion of uncoated steel reinforcement (ACI Committee 222
2001). Although some data exist, it is not well established what level of chlorides can exist before
coated steel reinforcement begins to corrode and what levels solid corrosion-resistant bars can tolerate;
it is always assumed that a limit exists. Sim (2014) compared the performance of different types of
steel reinforcement using macrocell specimens with cracked concrete specimens and ranked 10 types
of steel reinforcement in order of corrosion performance. In general, stainless steels showed the most
effective performance.
McDonald et al. (1998) conducted laboratory exposure tests on concrete specimens reinforced
with uncoated reinforcement, epoxy-coated reinforcement, stainless steel reinforcement, copper-clad
reinforcement, galvanized reinforcement, and spray metallic-clad reinforcement. The corrosion rates
of epoxy-coated bars were less than those of uncoated bars. The authors concluded that Type 316
stainless steel reinforcement should be considered as a means for achieving a 75- to 100-year ser-
vice life.
Michigan DOT (MDOT) compared the deterioration trends of bridge decks containing epoxy-
coated reinforcement, stainless steel reinforcement, and FRP reinforcement using the National
Bridge Inventory condition rating scale (Valentine 2015). The condition rating scale ranges from
0 (failed) to 9 (excellent). The study yielded the following conclusions:
• The service life of a bridge deck containing epoxy-coated reinforcement is estimated to be

approximately 86 years.
• The trend for bridge decks with stainless steel reinforcement is slightly better in the early stages
than the trend for bridge decks with epoxy-coated reinforcement.
• The trend for bridge decks with FRP reinforcement is not as good in the early years as the trend
for bridge decks with epoxy-coated reinforcement. This is attributed to the lower modulus

56
of elasticity of the FRP reinforcement, which may be resulting in increased cracking of

the bridge deck surface. The few FRP decks included in this study used different materials
and design.
AASHTO LRFD Specifications for Durability
Article 5.14 of the AASHTO LRFD Bridge Design Specifications (AASHTO 2017) addresses durabil-
ity of concrete structures. The principal aim of the AASHTO Specifications, with regard to durability,
is the prevention of corrosion of the reinforcing steel. The commentary states that design consider-
ations for durability include concrete quality, protective coatings, minimum cover, distribution and
size of reinforcement, details, and crack widths or prestressing. Reinforcement that is susceptible to
corrosion and used in concrete exposed to deicing salts or saltwater shall be protected by the use of
low-permeability concrete and concrete cover to the reinforcement. Specific information is provided
for concrete cover but not for permeability.
The commentary also states that the effects of salt intrusion and depassivation caused by carbon-
ation can be mitigated by using corrosion inhibitors, coated reinforcement, bimetallic reinforcement,
stainless steel reinforcement, or nonmetallic reinforcement, such as FRP composites. Article 5.14
does not mention controlling shrinkage and permissible crack widths, although crack widths are a
design consideration in other articles.
Permissible Crack Widths
Although the research described indicates that crack width may not be that significant when it
comes to corrosion, recommendations for limiting crack widths have existed for many years and
are still in use today. For example, Tadros et al. (2010) summarized permissible maximum crack
widths developed between 1935 and 1970 and generally used to control flexural cracking in beams.
Values ranged from 0.001 to 0.080 in., depending on the application and exposure conditions. Their
analysis of the recommendations indicated that most flexural crack widths in beams, at a 40-ksi
tensile stress in the reinforcement, ranged from 0.005 to 0.010 in.
ACI Committee 224 (2008) provides a table of reasonable crack widths in reinforced concrete
under service loads, as shown in Table 7. A footnote to the table states that a portion of the cracks
in a structure will exceed these values, and with time, a significant portion can exceed these values.
These crack widths are not always a reliable indication of the corrosion deterioration to be expected.
A larger cover, which will lead to wider surface crack widths, may be preferable for corrosion control
in certain environments (ACI Committee 224 2008).
Article 5.6.7 (formerly 5.7.3.4) of the AASHTO LRFD Bridge Design Specifications, which
addresses control of cracking by distribution of reinforcement, is indirectly based on crack widths
of either 0.017 or 0.013 in., depending on the selected exposure condition. The commentary states
that “Previous research indicates that there appears to be little or no correlation between crack width
and corrosion.”
Table 7
Reasonable Crack Widths
Exposure Condition Crack Width (in.)
Dry air or protective membrane 0.016
Humidity, moist air, soil 0.012
Deicing chemicals 0.007
Seawater, and seawater spray, wetting 0.006
and drying
Water-retaining structures 0.004
Source: ACI Committee 224 (2008).

57
Determination of Bar Spacing to Control Crack Widths
Over the years, different equations have been developed for the calculation of crack widths in
concrete components (Modjeski and Masters et al. 2015). Most of these equations are based on an
analysis of crack widths measured on laboratory test specimens loaded in flexure.
The first equation relating to bar spacing and crack width to be used in U.S. bridge specifica-
tions was the Gergely-Lutz equation (Gergely and Lutz 1968). It was based on a statistical analysis
of experimental data. The original equation for predicting crack width, wc, was
wc = 0.076bs fs 3 dc A (15)
where
wc = maximum probable crack width at the tension face (in.);

bs = ratio of flexural strain at the extreme tension face to the strain at the centroid of the
reinforcement;
fs = stress in steel reinforcement (ksi);
reinforcement located closest thereto (in.); and
A = average effective concrete area per bar of the flexural tension reinforcement (in.2). For a
single layer of reinforcement of constant spacing, the term, A, simplifies to 2dc s, where
s = bar spacing.
h − kd
bs = (16)
d − kd
where
h = overall thickness or depth of the beam (in.);

k = distance from neutral axis to compression face divided by the effective depth of the beam
(in.); and
d = effective depth of the beam (in.).
The AASHTO Standard Specifications (AASHTO 2002) and the subsequent LRFD Specifica-
tions (AASHTO 1994) included the Gergely-Lutz equation in a slightly rearranged form. The crack
width variable and the bs factor were consolidated into a single Z-factor, and the equation was written
in terms of allowable stress. Using an approximate limiting crack width of 0.016 in. and an average
bs factor of 1.2 resulted in
Z
fsa = (17)
( d c A)
13
where
fsa = allowable reinforcement stress (ksi);

Z = factor
= 170 for moderate exposure conditions
= 130 for severe exposure conditions,
with the remaining terms as defined previously.
Based on physical phenomenon, Frosch (1999) developed the following equation to predict crack
widths:
()
2
fs
( dc ) + 2s
2
wcu = 2 bs (18)
Es

58
where
wcu = maximum crack width for uncoated reinforcement (in.);

fs = stress in steel reinforcement (ksi); and
Es = modulus of elasticity of reinforcing bars (ksi),
with the remaining terms as defined previously.
The equation can be rewritten to solve for maximum permitted reinforcement bar spacing as follows:
2
w E 
s = 2  cu s  − ( dc )2 (19)
 2 fsb s 
where
bs = 1.0 + 0.08 dc . (20)
Frosch compared crack widths calculated by his equation with existing test data for reinforcement
stress levels ranging from 20 to 50 ksi. Based on crack widths between 0.016 and 0.021 in., Frosch
proposed the following simplified design equation:
 d 
s = 12a s 2 − c  ≤ 12a s (21)
 3a s 
where
36
as = gc (22)
fs
as = reinforcement factor; and

gc = reinforcement coating factor: 1.0 for uncoated reinforcement and 0.5 for epoxy-coated rein-
forcement, unless test data can justify a higher value.
Based on a review of past research, parametric studies, and various crack width predictive methods,
DeStefano et al. (2003) proposed the following equation:
700 ge gr
fss = ≤ 0.8 f y (23)
bs ( s + 2 dc )
where
fss = calculated tensile stress in steel reinforcement at the service limit state (ksi);
ge = exposure factor; and
gr = reinforcement factor
= 0.75 for smooth welded wire reinforcement
= 1.00 for all other types of reinforcement.
dc
bs = 1 + (24)
0.7 ( h − dc )
The upper limit of 0.8fy on the allowable stress was proposed to provide a factor of safety against
permanent yielding of the reinforcement under service loads. It is similar to that stipulated for steel
flexural members in Article 6.10.4.4.2 of the AASHTO LRFD Specifications (AASHTO 2014). The
paper (DeStefano et al. 2003) compares their equation with various design equations but does not
compare the equation directly with test data.

59
A rearrangement of the Equation 23 results in
700 ge gr
s= − 2 dc (25)
bs fss
With gr = 1.0, this equation becomes Equation 5.6.7-1 (formerly 5.7.3.4-1) in the 2017 AASHTO
LRFD Specifications (AASHTO 2017):
700 ge
s≤
bs fss
− 2 dc ( 5.6.7-1) (26)
In certain situations involving higher-strength reinforcement or large concrete cover, the use of
Equation 5.6.7-1 can result in small or negative values for s. Therefore, the 2016 Interim Revisions
(AASHTO 2016) introduced a limit that for calculation purposes dc need not be taken greater than
2 in. plus the bar radius and that s need not be less than 5 in. to control flexural cracking.
Equation 5.6.7-1 contains an exposure factor, ge, with suggested values of 1.0 or 0.75 depending on
the exposure condition. This same factor could be used to address different types of corrosion-resistant
reinforcement, or a new factor could be added to the equation similar to the gr in Equation 25. The fac-
tors could also vary depending on the desired service life of the structure. For this approach to be imple-
mented, additional research and data are needed to determine the appropriate values for the factors.
Service Life
Service life for bridges is defined by AASHTO as the period of time the bridge is expected to be in
operation (AASHTO 2017). At the present time, there are no U.S. standards or guidelines in place
to establish performance criteria for service life design. However, this may change in the future as a
result of an AASHTO and FHWA program to promote the use of service life design.
The Second Strategic Highway Research Program produced a “Design Guide for Bridges for
Service Life” (Azizinamini et al. 2014). The guide provides information, guidance, and procedures
to systematically approach service life and durability for new and existing bridges. It is expected that
the guide will be expanded, modified, and progressively embraced at different project and program
levels by the bridge and structures community.
Many factors can limit the service life of a bridge, but a major factor is corrosion of steel rein-
forcement caused by deicing chemicals or saltwater. Prediction of service life based on corrosion of
reinforcement generally is based on a two-part model: an initiation phase, during which chloride ions
build up at the level of the reinforcement until a critical concentration is reached, and a propagation
phase, during which the reinforcement corrodes (Bartholomew 2015).
The duration of the initiation phase depends on the chloride concentration at the concrete surface,
the rate at which the chloride ions penetrate the concrete, the distance that the chloride ions have to
travel, and the critical chloride concentration for the initiation of corrosion. For most bridges, the
only variable that is well defined is the distance that the chloride ions have to travel. Consequently,
a deemed-to-satisfy approach is usually taken by specifying a minimum concrete cover and a maxi-
mum permeability. All of this assumes that the concrete is not cracked. If service lives of 100 years
are to be predicted with any degree of reliability, analytical models or design procedures that include
the presence of cracks in the concrete are needed.
Although there are controversial findings about the impact of crack width on corrosion rate, gen-
eral agreement exists that cracking reduces the time to corrosion initiation (TRB 2006). The local-
ized corrosion at the cracked areas leads to additional longitudinal surface cracking, delamination,
and debonding, which ultimately result in a reduction in the strength and stiffness of the structure.
Thus, it is desirable to control crack widths to an acceptable level even though there is no consensus
on the size of allowable crack widths.

60
According to Nair et al. (2016a), early deterioration of concrete bridge decks has serious implica-
tions both financially and with regard to public safety. A shortened service life of the bridge deck,
higher maintenance costs, increased frequency of maintenance, and corrosion of reinforcing steel
are some of the consequences of deck cracking. The dollar impact of corrosion on highway bridges
is considerable. The average annual direct cost of corrosion for highway bridges was estimated to
be $8.29 billion (Yunovich et al. 2005). Thus, the corrosion of the reinforcing steel that is attributed
primarily to bridge deck transverse cracking and the application of deicing chemicals containing
chloride is costly (McLeod et al. 2009).
Conclusions About the Influence of Cracking

on Long-Term Bridge Performance
Research has established that the presence of cracks in concrete allows chloride ions to reach the
reinforcement in less time than in uncracked concrete. Consequently, corrosion of noncorrosion-
resistant reinforcement will begin earlier in cracked concrete than in uncracked concrete. However,
most analytical models assume uncracked concrete.
The use of corrosion-resistant reinforcement prolongs the time to initiation of corrosion and thus
increases service life. Stainless steel provides the longest life, although coated bars, such as epoxy-
coated ones, can provide sufficient protection for many applications. Additional work is needed to be
able to predict service life with cracked concrete and the different types of reinforcement available.
Currently, no U.S. standards exist to predict long-term performance and service life.

61
chapter seven
Case Examples
This chapter contains case examples describing how four states have looked for solutions for pre-
venting or reducing cracking in concrete bridge decks.
California Department of Transportation
The following case example is extracted from an article by Maggenti et al. (2013) and is published
with permission of the American Concrete Institute.
Between 2001 and 2003, six new bridges with CIP concrete decks on spliced precast concrete
bulb-tee girders were constructed on I-80 near Truckee, California. The concrete had a w/cm of 0.36,
cementitious materials content of 752 lb/yd3 with 25% fly ash, and 6% air content.
After the first few decks were constructed, multiple transverse cracks at about 2-ft centers were
visible. Beginning in late summer of 2002, deck mixtures were modified to include SRAs. This caused
a dramatic reduction in cracking. The following construction season, the remaining structures were
constructed using an SRA in the deck concrete. The decks constructed using SRAs remained free of
visible cracking for several years.
Following this simple, yet effective, adjustment to the mixture design, specifications were written
for the deck concrete for the Angeles Crest Bridge on SR-2 in Los Angeles County, in the mountains
northeast of Los Angeles, California. This is a 208-ft, single-span bridge with the deck cast on six
8-ft-deep spliced precast, prestressed concrete bulb-tee girders spaced at 6.5-ft centers. The specifi-
cations called for a 28-day concrete compressive strength of 5.0 ksi and a 6% air content. Construc-
tion was completed in 2008 using a deck mixture with 767 lb/yd3 of cementitious materials and an
SRA. Upon later inspection, only a few hairline shrinkage cracks were observed at the westerly end.
The same result was achieved on the 2007 emergency replacement of the fire-destroyed bridge
spans at the MacArthur Maze in Oakland, California. This replacement was completed in a mere
26 days using a deck mixture made up of SRAs, 800 lb/yd3 of cementitious material, water reducers,
and a Type C accelerating admixture. The deck was cast on steel girders with headed studs to achieve
composite action. By 2013, no cracking had been reported on this replacement deck span, whereas
transverse cracks have been noted every few feet on all adjacent deck spans, which used a cementi-
tious materials content of 564 lb/yd3 and a 1.5-in. maximum nominal aggregate size. These projects
demonstrated that SRAs could eliminate the need to specify low-strength concrete, long curing times,
a low w/cm ratio, or large aggregates.
In 2011, a 5-in.-thick concrete deck was placed on precast concrete box beams over Craig Creek
on SR-99 near Red Bluff, California. The concrete mixture was designed to develop a 3-day strength
of 4.0 ksi, using 705 lb/yd3 of portland cement, a water-cement ratio of 0.39, an SRA, and synthetic
macrofibers at 3.0 lb/yd3. The project was used to study accelerated bridge construction through HPC
and only 3 days for moist curing. No visible cracking was noted during inspection after 14 months of
service. It was concluded that a high-quality, durable deck can be successfully and rapidly constructed.
The Caltrans Standard Specifications now require limiting the shrinkage of deck concrete to a
maximum of 0.032% (320 millionths) after 28 days of drying, a minimum amount of an SRA, a dose

62
of polymer fibers, and stricter curing requirements. In 2013, a Caltrans fact sheet estimated that
Caltrans was spending $50 million annually on sealing cracks in concrete bridge decks. The increase in
concrete costs after implementing the new requirements is estimated to be about $2 million annually.
In 2012, the calculated increase in costs was $0.89/ft2.
Kansas Department of Transportation
In 2003, Kansas DOT (KDOT) became the lead state of a pooled fund study with 18 other states
and the FHWA. The goal of the study was to construct low-cracking, high-performance concrete
(LC-HPC) bridge decks (Browning and Darwin 2007; Browning et al. 2009). By 2012, 16 bridges in
northeast Kansas and seven in other participating states had been constructed using some or all of the
new specifications (Darwin et al. 2012). Most LC-HPC bridge decks had a companion non–LC-HPC
bridge deck so comparisons could be made.
Evaluation of more than 150 bridge decks, most supported by steel beams, has demonstrated that
crack density increases with time. The bridge decks that performed well in the first 3 years performed
well at later ages. Monolithic decks tended to perform better than did those constructed with over-
lays because cracks in the subdeck reflected through the overlays, and shrinkage of the overlay was
restrained by the subdeck (Darwin 2014).
Other conclusions from the research indicated the following:
• Concrete mixes with greater paste content exhibited greater drying shrinkage.
• The restraint to drying shrinkage was greater for steel beam bridges than for bridges with precast,
prestressed concrete beams.
• Increased concrete slump leads to increased settlement cracking.
• Increased air content reduces cracking.
• Increased concrete strength results in more cracking.
• Higher creep is beneficial in reducing cracking.
• Extra finishing leads to increased plastic and shrinkage cracking.
• Rapid evaporation of bleed water increased plastic shrinkage cracking.
• Large temperature differences between the deck concrete and the beams at time of placement
result in thermal cracking.
• The use of stay-in-place forms doubles the moisture gradient.
Based on the previous information, specifications for LC-HPC for bridge decks were developed,
including the following requirements:
• Cementitious materials content of 500 to 540 lb/yd.3 (This was later changed to a maximum of
540 lb/yd3.)
• Use of only Type I/II cement.
• Maximum w/cm ratio of 0.42. (This was later revised to 0.44 to 0.45.)
• Paste content (total volume of water and cement) less than 25%.
• Maximum aggregate size of 1 in.
• Combined aggregate gradation optimized for uniform size distribution.
• Maximum aggregate absorption of 0.7%.
• Designated air content of 7.0% to 9.0% (with 6.5% to 9.5% acceptable).
• Compressive strength at 28 days of 3.5 to 5.5 ksi.
• Designated slump of 1.5 to 3.0 in. (with a maximum of 3.5 in. acceptable).
• Concrete placement temperature of 55°F to 70°F.
• Evaporation rate less than 0.2 lb/ft2/h.
• Wet curing with one layer of presoaked burlap starting within 10 minutes of concrete strike off
followed by a second layer of burlap within 5 minutes, as shown in Figure 17.
• Fourteen days of wet curing followed by application of a curing compound to be unmarred
for 7 days.
• A qualification slab with dimensions equal to the bridge width, full slab depth, and 33 ft long to
be cast before bridge deck placement to demonstrate the contractor’s capabilities.

63
FIGURE 17 Application of precut, rolled, wet burlap within 10 min-

utes after concrete finishing (Courtesy: David Darwin, University
of Kansas and Concrete Bridge Views, published jointly by FHWA
and the National Concrete Bridge Council).
Curing during cold weather requires extra precautions to reduce cracking caused by thermal
stresses. To prevent cracking, the difference between the concrete and steel girder temperatures
must be kept within a tolerable range. During the first 72 hours of the curing period, if the ambient
air temperature falls below 40°F, protective measures must be taken to maintain the temperature of
the concrete and the girders between 55°F and 75°F. This may include using straw or extra burlap
on the concrete, and wrapping the girders with plastic and using propane heaters. Similar protec-
tive measures must be taken when the ambient air temperature is expected to drop more than 25°F
below the placement temperature of the concrete during the first 24 hours after placement. After
the first 72 hours, the contractor has the option of maintaining the temperature throughout the cur-
ing period or extending the curing period to account for periods during which the air temperature
drops below 40°F.
Two of the primary lessons learned were that these concrete specifications can be implemented
at a reasonable cost and that the low-paste concrete mix is workable, placeable, and finishable in
the field (Browning et al. 2009). Concrete strengths were about 4.0 ksi. The establishment of a good
working relationship among owners, inspectors, contractors, and concrete suppliers was of prime
importance for the successful construction of an LC-HPC bridge deck. All participants must clearly
communicate their expectations and successfully meet the specifications (Browning et al. 2009).
Bridge decks constructed with LC-HPC had less than 10% of the cracking found in traditional
bridge decks.
Sixteen LC-HPC bridge decks and 13 control decks were inspected in 2014 and 2015 as part of
the continuing program to monitor cracking in these bridge decks (Alhmood et al. 2015). Based on
the results of these inspections, the following conclusions were developed:
• LC-HPC bridge decks exhibit less cracking than do the matching control decks in most cases.
• Only one bridge deck had a higher overall crack density than its control deck.
• The most common crack type is transverse cracking. Cracks of this type appear to run parallel
to the top layer of the deck’s reinforcement.
• Near the abutments, cracks usually propagate perpendicular to the abutments.
As part of the continuing LC-HPC program, the effects of SRAs, SCMs, prewetted LWA, slag
cement, silica fume, and air entraining admixtures on concrete properties were evaluated in laboratory
mixes (Reynolds et al. 2009; Pendergrass and Darwin 2014; Yuan et al. 2015). Shrinkage-reducing
admixtures reduced early-age and long-term shrinkage, with the reductions in shrinkage concentrated

64
within the first 90 days. Prewetted LWA reduced early-age and long-term shrinkage (Browning et al.
2011). Shrinkage was also reduced when slag cement was used at 30% by volume of the cementitious
materials and as silica fume was used at a nominal 3% by volume in conjunction with LWA and
slag cement.
Pennsylvania Department of Transportation
In 1995, Purvis et al. (1995) reported that increased cracking had been observed in newly constructed
concrete highway bridge decks in Pennsylvania. Consequently, PennDOT initiated a research project
to identify factors that may cause premature concrete cracking, relate these factors to PennDOT bridge
deck cracking, and recommend changes. Based on field observations and laboratory tests, the authors
concluded that the main cause of transverse cracking was a combination of thermal shortening and
drying shrinkage. The following recommendations were made:
• Control the temperature difference between the deck and the girders to less than 22°F for at
least 24 hours after the concrete is placed.
• Require that deck concrete have a shrinkage not greater than 700 millionths after 4 months
of drying.
To comply with the temperature requirement in hot weather, the authors recommended the use of
a retarder and to cover the deck concrete with wet burlap within 30 minutes after placing to minimize
heat buildup from the sun. It was also preferable to place concrete at night.
To comply with the temperature difference in cold weather, the authors recommended that the air
underneath the deck be heated to 55°F to 75°F to raise the temperature of the beams and reduce the
temperature difference with the deck concrete. At the same time, the top surface of the deck is to be
insulated to maintain the same temperature range.
To comply with the shrinkage requirement, the authors suggested the use of hard aggregates, such
as quartz, dolomite, and limestone; maximum coarse aggregate absorption of 0.5%; maximum fine
aggregate absorption of 1.5%; a lower water content in combination with a water-reducing admix-
ture; a lower cement content; and a Type II cement. At that time, the specifications allowed a water
content of 323 lb/yd3 and a maximum cement content of 752 lb/yd3.
The Kernville viaducts in Pennsylvania consist of two 2,700-ft, 27-span, curved, continuous steel
girder bridges with an 8-in.-thick reinforced concrete deck. The westbound lanes were built in 2001. A
crack survey of the decks after construction of the westbound lanes showed that there were 237 cracks
at an average spacing of 6.4 ft in the positive moment regions and 227 cracks at an average spacing
of 5.1 ft in the negative moment regions (Spangler and Tikalsky 2006). Cracks had a width generally
greater than 0.04 in., with numerous cracks being larger than 0.12 in.
Below placement of the concrete deck for the eastbound lanes, the following changes to the con-
crete mixtures were developed:
• Increase the w/cm ratio from 0.40 to 0.43.

• Decrease the cementitious materials content from 650 to 588 lb/yd3.
• Decrease the percentage of ground granulated blast-furnace slag from 50% to 42% of the total
cementitious materials content.
• Decrease the target slump from 6.0 to 4.5 in.
• Reduce the maximum concrete temperature at time of placement from 80°F to 70°F.
The following construction changes were also implemented:
• Place positive moment regions successively on one day, followed by placement of negative
moment regions 3 or more days later.
• Apply moist curing immediately after concrete finishing and maintain for 10 days.
• Apply a pigmented curing compound at the end of the moist curing period.
• Increase vigilance in quality control and quality assurance operations.
65
After construction of the eastbound lanes, crack surveys made immediately after curing and in
subsequent months showed a dramatic reduction in the frequency and width of cracks. Early-age
cracking immediately after curing was nearly eliminated by the changes in mixture design and con-
struction practices. At 7 months, 174 total cracks were recorded on the eastbound deck, compared
with 464 cracks on the westbound deck. Most of the cracks in the eastbound lanes were narrower
than 0.005 in. during cold weather conditions.
In another research project, Manafpour et al. (2016) reported data from field investigations of
203 bridge decks in Pennsylvania with ages to 50 years. The data were used to identify factors that
contribute to early-age cracking and assess the effect of cracks on the long-term durability of bridge
decks. The following main conclusions were drawn:
• Higher concrete compressive strengths correlated with higher crack densities in the deck. The
authors advised a maximum limit on the concrete compressive strength at 7 or 28 days (e.g.,
4.0 or 5.0 ksi, respectively).
• Lower total cementitious materials content and higher SCMs content resulted in less cracking.
The authors advised a maximum limit on the cementitious materials content (e.g., 620 lb/yd3)
and encouraged the use of SCMs to reduce heat of hydration, increase electrical resistivity, and
prevent alkali–silica reaction. It was acknowledged that high SCM contents could pose poten-
tial challenges with strength gain in cooler seasons.
• Decks constructed with half-width procedures to allow one half of the bridge to remain open
cracked four times more than did decks constructed with the full width at one time and the use
of traffic detours.
Washington State Department of Transportation
In a survey for NCHRP Synthesis 441 (Russell 2013), Washington State DOT (WSDOT) reported
that the performance of HPC in CIP bridge decks was worse than that of conventional concrete. This
was based on an observed increase in the amount of cracking, which appeared to be associated with
the required use of fly ash. However, the cracking may have been caused by the use of girders with
wide top flanges. These girders provide more restraint to the differential shrinkage between the deck
concrete and the girders. WSDOT reported that no strategy employed was effective in minimizing
cracking. The use of evaporation retardants was found to be the least effective.
At that time, the WSDOT Standard Specifications for bridge deck concrete required a minimum
cementitious materials content of 660 lb/yd3 with a fly ash content between 10% and 20% or a
slag cement content between 10% and 30% of the total cementitious material. If both fly ash and
slag cement were included, the maximum allowable content increased to 40%. The use of a water-
reducing admixture and a retarding admixture was required. The use of a high-range, water-reducing
admixture was permitted (Russell 2013).
In the 2010 Standard Specifications, WSDOT increased the nominal maximum aggregate size
from ¾ in. to 1 in. In 2011, WSDOT introduced a performance-based specification for bridge decks
to eliminate or reduce early-age restraint cracking in bridge decks (Ferluga and Glassford 2015).
Bridge decks constructed with this revised concrete specification are referred to as “Performance
Based Bridge Decks.”
The revised specification no longer had a minimum cementitious materials content and did not
require the use of fly ash. Another significant change was to increase the nominal maximum aggre-
gate size from 1 to 1½ in. The performance-based requirement for minimum concrete compressive
strength remained in the specification at 4.0 ksi at 28 days. Performance limits on permeability,
shrinkage, and surface scaling, with an optional requirement for freeze–thaw durability to reduce
prescribed air content, were included. In addition to the performance limits, modulus of elasticity
and density were required to be measured, but no limits were specified.
In addition to revisions to the mix design, changes were made to the placement, finishing, and
texturing portions of the specification. The goal of these revisions was to begin adequate wet curing
as soon as possible. The original specifications for placing and texturing typically resulted in a delay
66
in the application of wet burlap to the surface of the bridge deck. This delay occurred because the
texturing was done by tining transverse grooves with a metal comb and could not occur until the
concrete was sufficiently stiff. After the bridge deck was tined, curing compound was applied. Fol-
lowing the initial setting of the deck concrete, the presoaked burlap and soaker hoses were applied
and kept in place for 14 consecutive days.
Revisions to the curing portion of the specification now require fogging the deck immediately
after the finishing machine passes. Tining of the bridge deck was eliminated and presoaked burlap
applied almost immediately “without damaging the finish, other than minor marring of the concrete
surface.” The use of curing compound was explicitly forbidden. Fogging must continue until the con-
crete has achieved initial set when soaker hoses are added. The wet burlap and soaker hoses remain
in place for 14 consecutive days.
Another change to the specification required that the concrete temperature at the time of place-
ment be between 55°F and 75°F. The original specification limited concrete temperature at time of
placement to between 55°F and 90°F.
In the spring of 2015, the undersides of 27 bridge decks constructed since 2007 were visually
inspected for cracks: 15 bridges had been constructed using the performance-based specification, and
12 had been constructed using the traditional WSDOT specification. Seven single-span prestressed
concrete bridges, six two-span prestressed concrete bridges, 10 multispan prestressed concrete bridges,
and four steel plate girder bridges were selected. All bridges used I-girders for the ability to inspect the
underside of the decks between the girders. The gathered information was converted into “crack inten-
sity” diagrams to illustrate the severity and location of cracking for each bridge deck. The cracks were
identified from the underside of the decks. Cracks on the top of the deck were not included.
As illustrated in Figure 18, the performance-based concrete specification generally resulted in

fewer visible cracks in bridge decks than did the traditional concrete specification. A few of the tradi-
tional bridge decks performed similarly to the performance-based bridge decks, but this appeared to
be the exception, not the rule. Only one of the performance-based concrete decks had a high intensity
of cracking. It was unclear what contributed to the poor performance of this particular bridge deck.
The performance-based concrete specification resulted in fewer cracks in decks on precast concrete
girders compared with decks on steel girders.
The study revealed that cracking of bridge decks varied within the same bridge. In some cases,
it appeared to vary within the same concrete placement. The authors concluded that there are many
(a) (b)
FIGURE 18 Cracking in Washington State bridge decks: (a) before

and (b) after (Courtesy: Washington State DOT).

67
variables that affect the cracking performance of a bridge deck, and these may change during the
construction of the bridge. A similar effect was observed by Mokarem et al. (2009).
A secondary objective of the WSDOT bridge study was to identify trends or issues with the
performance-based specification that could be improved. Mix design, test data, and temperature
information were gathered for the performance-based bridge decks evaluated in the study. No cor-
relation could be made between the data and crack intensity; however, improvements in data col-
lection on future projects may provide better data to identify trends or issues. Ultimately, based on
the WSDOT study, no significant changes to the bridge deck concrete specifications were needed
(Ferluga and Glassford 2015). The performance-based specification became part of the WSDOT
Standard Specifications in 2015.

68
chapter eight
Conclusions and Suggestions

for Future Research
Conclusions
Concrete cracking in bridges is complex and unlikely to be caused by a single effect. In some situ-
ations, cracking cannot be avoided. Nevertheless, crack quantities and widths can be minimized by
the careful selection of materials, proper reinforcement design details, and appropriate construction
practices.
Full-Depth, Cast-in-Place Concrete Bridge Decks
It is the consensus of bridge industry personnel that the primary causes of bridge deck cracking are
drying shrinkage of the deck concrete and temperature differences between the deck concrete and
the supporting beams. However, the industry does not have a good record for consistently, reliably,
and predictably producing concrete structures with minimal or no concrete cracking. The practices
described here have been identified previously as ways to reduce and control cracking, yet cracking
in bridge decks continues to be a major concern. Perhaps the real need is proper implementation of
these practices.
Practices recommended for reducing shrinkage and associated shrinkage cracking in cast-in-
place (CIP) concrete bridge decks are as follows:
• Using a w/cm ratio in the range of 0.40 to 0.45.

• Using a cement content not greater than 650 lb/yd3.
• Using the lowest quantity of water and cement paste in the concrete consistent with achieving
other required properties.
• Using the largest practical maximum size coarse aggregate and maximum coarse aggregate
content to reduce the water demand.
• Using an optimum combined aggregate gradation.
• Avoiding actual concrete compressive strengths greater than 6.0 ksi.
Practices recommended for reducing cracking from temperature differences include the following:
• Minimizing the temperature difference between the CIP concrete deck and the supporting steel
or concrete beams.
• Specifying and ensuring minimum and maximum concrete temperatures at time of placement
of 55°F and 75°F, respectively.
• Minimizing cement content.
Recommended design practices that can reduce the likelihood of cracking and control crack widths
include the following:
• Specifying the lowest acceptable concrete compressive strength.

• Specifying a minimum shrinkage of 300 to 350 millionths after 28 days of drying when tested
in accordance with AASHTO T 160.

69
• Specifying a placement sequence that will minimize tensile stresses in previously placed
concrete.
• Using the minimum bar sizes and spacings to control crack widths.
Recommended construction practices that can reduce the likelihood of deck cracking include the
following:
• Where practical, using a placement sequence that will minimize tensile stresses in previously
placed fresh concrete.
• Using windbreaks and fogging equipment, when necessary, to minimize surface evaporation
from fresh concrete.
• In hot or low humidity conditions, placing concrete at night.
• Applying wet curing procedures immediately after concrete finishing and maintaining the
surface wet for at least 7 days.
• Applying a curing compound after the wet curing period to slow shrinkage and enhance the
concrete properties.
Other practices that some state agencies reported to have been effective include the following:
• Using internal curing.

• Using an SRA.
• Including SCMs in the concrete.
• Using a shrinkage-compensating concrete.
Overall, no single practice can be used to enhance concrete bridge deck performance.
When the structural system of the bridge includes skewed supports, diagonal cracks are likely to
occur near the supports. When the structural system of the bridge includes continuity over the sup-
ports, negative moment transverse cracks are likely to occur. When construction joints are present,
cracks are likely to occur at the joints. To control crack widths and spacing in these situations, using
the minimum bar sizes and minimum bar spacings that are practical is recommended.
The main concern with the use of partial-depth, precast concrete panels with a CIP topping is the
reflective cracking that occurs in the topping above the edges of the panels. This type of cracking may
be reduced by saturating the surface of the panel before casting the topping, special joint detailing,
and delaying erection of the panels until most of the creep and shrinkage have occurred. Crack widths
can be controlled by the reinforcement in the topping. Nevertheless, research is needed to clearly
determine the primary factors causing reflective cracking and identify ways to reduce or eliminate it.
Full-depth panels generally are pretensioned in the transverse direction of the bridge and may be
posttensioned in the longitudinal direction. Although the use of two-directional prestressing offers
the potential to produce a crack-free bridge deck, the results from the survey indicate that this is not
always accomplished. Additional research is needed on this topic to provide a solution for crack control
of prestressed and nonprestressed panels.
Adjacent Precast Concrete Box Beam Bridges and Slab Beam Bridges
Lateral ties are used in adjacent precast concrete box beam bridges to tie adjacent beams together.
As such, the ties function to control the crack widths. The degree of restraint varies from requiring
a minimum compressive stress across the longitudinal joint to providing a passive tie. NCHRP Proj-
ect 12-95 is ongoing, with the objective of developing guidelines for the design and construction of

70
connection details for adjacent precast concrete box beam bridges to eliminate cracking and leakage
in the longitudinal joints between adjacent boxes.
Pretensioned Concrete Beams
End zone cracking in prestressed concrete beams is an uncommon occurrence but can be prevented
by modifying the detensioning sequence. Cracks that occur can be controlled through the use of split-
ting and confinement reinforcement in the end zone region. Vertical cracking that occurs in the webs
before transfer can be reduced by providing longer lengths of free strand in the bed.
Nonprestressed Concrete Beams
Cracking in nonprestressed concrete beams is almost inevitable but is controlled by providing minimum
amounts of reinforcement to control crack widths.
Substructures
In general, cracking in substructures is an uncommon occurrence. Limiting the maximum stress in the
reinforcement under service loads provides a means of crack width control. Design of deep compo-
nents using the strut-and-tie method rather than the sectional design method along with the required
reinforcement should provide improved crack control. It is recommended that a thermal control plan
be developed to control thermal cracking in large members.
Effect of Reinforcement Type
Epoxy-coated reinforcement continues to be the primary type of reinforcement used for corrosion
protection, although agencies have used zinc-coated, stainless-steel–coated, solid stainless steel,
low-carbon chromium, and FRP reinforcement. The use of high-strength reinforcement leads to
wider cracks unless an upper limit is placed on the allowable tensile stress in the reinforcement under
service loads. Narrower crack widths result from using smaller diameter bars at a closer spacing. The
AASHTO LRFD Specifications address the need to provide minimum amounts of reinforcement to
ensure sectional strength. However, the LRFD articles do not encompass the full range of reinforce-
ment types that are available today.
Effect of Cracking on Long-Term Performance
Research has established that corrosion of conventional uncoated reinforcement will begin earlier in
cracked concrete than in uncracked concrete. However, most analytical models assume uncracked
concrete.
The use of corrosion-resistant reinforcement prolongs the time to initiation of corrosion and thus
service life. Stainless steel provides the longest life, although coated bars, such as epoxy-coated
ones, can provide sufficient protection for many applications.
Because the effect of cracking on service life is not well-defined, additional work is needed to be able
to predict service life with cracked concrete and the range of reinforcement types available. Currently,
no U.S. standards exist to predict long-term performance and service life.
Suggestions for Future Research
This synthesis has identified that many of the existing articles in the AASHTO LRFD Bridge Design
Specifications for crack control were developed before the availability and use of certain types of
reinforcement that exist today. These include steel reinforcement with a specified yield strength
between 60 and 100 ksi, some types of corrosion-resistant reinforcement, and FRP reinforcement.

71
The application of the existing articles to control flexural cracking in structures with these new types
of reinforcement may not be appropriate and in some cases can result in unnecessary increased costs
or impractical designs. Consequently, a fresh look is needed to ensure that design provisions for
flexural crack control are provided that address all types of reinforcement.
Because most transverse cracks in full-depth concrete decks are caused by restrained shrinkage,
there is a need to develop specifications to control shrinkage cracking. These may or may not be similar
to the specifications for control of flexural cracking.
Service life predictions generally are based on uncracked concrete with uncoated steel reinforce-
ment. Additional work is needed to be able to predict service life with cracked concrete and the different
types of reinforcement available.
This synthesis has identified the need to determine the primary factors causing the reflective crack-
ing in partial-depth, precast concrete panels and ways to reduce or eliminate it such cracking. Research
is needed to provide a solution for crack control of prestressed and nonprestressed full-depth panels.
Responses to the survey for this synthesis provided the following suggestions for future research
and development programs related to concrete cracking:
• Coordination between designers and materials experts in identifying causes of cracking.

• Determination of permissible crack widths associated with different size reinforcing bars.
• Comparative study of deck cracking with partial-depth, precast concrete deck panels compared
with conventional full-depth CIP decks and methods for reducing reflective cracking when
partial-depth, precast concrete deck panels are used.
• Role of reinforcement layout on crack control for high-strength concrete.
• Use of additional reinforcement or control joints at the center of floor beams to mitigate
cracking.
• Investigation of methods for reducing end-region cracking in pretensioned girders.
• Investigation of how to reduce and control vertical cracks in CIP traffic barriers on top of a
concrete deck slab.
• Research to address shrinkage and cracking potential of concrete mixes, particularly HPC and
SCC. Research to include multiple admixtures, expansive components, SRAs, SCMs, and
internal curing.
A research problem statement to address the control of flexural and shrinkage cracking by distribu-
tion of reinforcement is provided in Appendix D. The statement incorporates several of the suggestions.
Respondents also identified ongoing research at their agency. The responses are tabulated in
Question 25 of Appendix B.

72
Abbreviations
ACI American Concrete Institute

ASTM ASTM International
CIP cast in place
CSA Canadian Standards Association
DOT department of transportation
FRP fiber-reinforced polymer
GFRP glass fiber-reinforced polymer
HPC high-performance concrete
LC-HPC low-cracking, high-performance concrete
LRFD load resistance factor design
LWA lightweight aggregate
PCA Portland Cement Association
PCI Precast/Prestressed Concrete Institute
SCM supplementary cementitious materials
SCC self-consolidating concrete
SRA shrinkage-reducing admixture
UHPC ultra–high-performance concrete
w/cm water/cementitious materials

73
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79
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Referenced Standards by AASHTO
M 85 Standard Specification for Portland Cement

M 194 Standard Specification for Chemical Admixtures for Concrete
M 240 Standard Specification for Blended Hydraulic Cement
T 160 Standard Method of Test for Length Change of Hardened Hydraulic Cement Mortar and
Concrete
T 277 Standard Method of Test for Electrical Indication of Concrete’s Ability to Resist Chloride
Ion Penetration
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Referenced Standards by ASTM International
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Concrete Reinforcement
C672 Standard Test Method for Scaling Resistance of Concrete Surfaces Exposed to Deicing
Chemicals
C845 Standard Specification for Expansive Hydraulic Cement
C1116 Standard Specification for Fiber-Reinforced Concrete
C1157 Standard Performance Specification for Hydraulic Cement
C1761 Standard Specification for Lightweight Aggregate for Internal Curing of Concrete

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Appendix A
Survey Questionnaire
The following survey for this synthesis was mailed in January 2016 to 50 U.S. state highway agencies,
the District of Columbia, and 12 provincial highway agencies in Canada to collect information about their
experiences with concrete cracking and their practices to prevent and control concrete cracking. Forty-five
responses were received.
Synthesis Survey
Topic 47-01
1. INTRODUCTION
Please enter the date (MM/DD/YYYY).________________________________
Please enter your contact information.

First Name__________________________________________________
Last Name__________________________________________________
Title_______________________________________________________
Agency/Organization_________________________________________
Street Address_______________________________________________
Suite______________________________________________________
City_______________________________________________________
State______________________________________________________
Zip Code___________________________________________________
Country____________________________________________________
E-mail Address______________________________________________
Phone Number______________________________________________
Fax Number________________________________________________
Mobile Phone_______________________________________________
URL_______________________________________________________
2. GENERAL
1. Which of the following types of concrete cracking has your agency experienced in the past five
years on bridges with precast, prestressed concrete beams? If your agency does not use a particular
system, check Not Applicable.
Not
Type of Cracking Never Infrequently Frequently Always Unknown
Applicable
Cracking in cast-in-place concrete decks
with removable formwork
with stay-in-place metal forms
on precast concrete deck panels
Cracking at locations other than the
connections in full-depth precast
concrete deck panels
Cracking at the connections in full-depth
precast concrete deck panels
Cracking in the cast-in-place concrete
decks above the longitudinal connections
in adjacent box beam or slab beam
bridges
Cracking in the longitudinal connections
between adjacent box beam or slab beam
bridges when a cast-in-place topping is
not used
Vertical cracks in pretensioned concrete
beams prior to transfer of prestressing
force
End splitting cracks in prestressed
concrete beams

84
2. Which of the following types of concrete cracking has your agency experienced in the past five years
on bridges with steel beams? If your agency does not use a particular system, check Not Applicable.
Not
Applicable
with stay-in-place metal forms
Cracking in cast-in-place concrete decks on
connections in full-depth precast concrete
deck panels
on bridges with concrete or steel beams?
Not
Applicable
Cracking in non-prestressed concrete beams
Cracking in pier caps
Cracking in columns or abutments
Cracking in pile caps
4. What lessons has your agency learned about controlling concrete cracking? Specific case studies
would be useful for the synthesis. Please list any reports or attach files in Question 29.
3. BRIDGE DECKS (Canadian participants go to Question 6.)
5. Does your agency use Article 5.7.3.4—Control of Cracking by Distribution of Reinforcement of

the AASHTO LRFD Bridge Design Specifications to determine maximum spacing of reinforcement
in bridge decks?
( ) Yes with no changes
( ) Yes with modifications
( ) No
If “Yes” or “Yes with modifications,” what value of the exposure factor, ge, does your agency use?
If your agency has modifications or design practices to supplement Article 5.7.3.4, what are they?
6. What strategies does your agency currently use to minimize cracking in full-depth, cast-in-place
concrete bridge decks?
Strategy Yes No
None
Specify minimum cementitious materials content
Specify maximum cementitious materials content
Specify minimum concrete compressive strength
Specify maximum concrete compressive strength
Specify a ratio between 7- and 28-day compressive strengths
Specify minimum concrete temperature at placement
Specify maximum concrete temperature at placement
Specify maximum concrete temperature during curing
Specify maximum water-cementitious materials ratio
Specify maximum slump
Specify maximum water content
Specify the use of a shrinkage-reducing admixture
Specify the use of a shrinkage-compensating concrete
Specify the use of fibers
Require use of the ACI surface evaporation nomogram
Require wind breaks during concrete placement
Require evaporation retardants
Specify internal curing
Require fogging during placement when evaporation rates are high
Specify a minimum wet curing period
Other
If “Other” or only used under special circumstances, please list.

85
7. What strategies to minimize cracking in full-depth cast-in-place concrete bridge decks have been
most effective?
least effective?
9. What is the frequency of use of the following cements in your agency’s concrete bridge decks?

AASHTO M 85 Type I and IA
AASHTO M 85 Type II and IIA
AASHTO M 85 Type II(MH) and
II(MH)A
AASHTO M 85 Type III and IA
AASHTO M 85 Type IV
AASHTO M 85 Type V
AASHTO M 240
ASTM C1157
10. What is the frequency of use of the following supplementary cementitious materials in your agency’s

Fly ash Class C
Fly ash Class F
Pozzolan Class N
Silica fume
Ground-granulated
blast-furnace slag
Other
If “Other,” please list.
11. What is the frequency of use of the following admixtures for cast-in-place concrete bridge decks?
Admixture Never Sometimes Often Always

AASHTO M 194 Type A—Water-reducing admixtures
AASHTO M 194 Type B—Retarding admixtures
AASHTO M 194 Type C—Accelerating admixtures
admixtures
admixtures
AASHTO M 194 Type F—High range water-reducing
admixtures
Corrosion inhibitors
Shrinkage-reducing admixtures
Expansive cement or components
12. What length of wet curing does your agency currently specify for cast-in-place concrete bridge
decks?
None 3 days 7 days 14 days Other

Check only one
If “None,” what method is used? If “Other,” state how long.
13. How is wet curing achieved?
14. Does your agency specify epoxy-coated reinforcement for concrete decks?
Reinforcement Yes No
Top layer
Bottom layer
Girder reinforcement projecting into the deck

86
15. What types of reinforcement with metallic coatings has your agency used in cast-in-place concrete
bridge decks?
( ) None ( ) Zinc coated ( ) Stainless steel coated ( ) Other
Explain any effect of their use on cracking.
16. Has your agency used solid stainless steel reinforcement in cast-in-place concrete bridge decks?
( ) Yes
( ) No
If “Yes,” how did its use affect deck cracking?
17. Has your agency used fiber-reinforced polymer (FRP) reinforcement in cast-in-place concrete
bridge decks?
( ) Yes
( ) No
18. Has your agency used ASTM A1035 reinforcement in bridge decks based on a yield strength of
100 ksi for design?
( ) Yes
( ) No
4. PRESTRESSED CONCRETE BEAMS (Canadian participants go to Question 21)
19. Does your agency use Article 5.10.10.1—Splitting Resistance of the AASHTO LRFD Bridge
Design Specifications to design the splitting reinforcement at the ends of beams?
( ) Yes with no modifications
( ) No
20. Does your agency use Article 5.10.10.2—Confinement Reinforcement of the AASHTO LRFD
Bridge Design Specifications to design the confinement reinforcement at the ends of beams?
( ) Yes with no modifications
( ) No
5. Substructures
21. Does your agency use the same crack control criteria for substructures and superstructures?
( ) Yes
( ) No
If “No,” what criteria are used for substructures?
22. If your agency has experienced cracking in pier caps, please describe the type of pier cap (rect-
angular, inverted tee, hammerhead, etc.) and type of cracking (flexure, shear, temperature, etc.)?
23. If your agency has experienced cracking in columns or abutments, please describe the type of
cracking (flexure, shear, temperature, etc.)?
24. If your agency has experienced cracking in pile caps, please describe the type of cracking (flexure,
shear, temperature, etc.)?

87
6. Research
25. Please list any research in progress by your agency related to concrete cracking.
26. Please list any recommendations for future research needs related to concrete cracking.
27. Please list any agency research reports that document the performance in bridges with regard to
control of concrete cracking and are available to be referenced in this synthesis. Case studies are
of particular interest. Please provide links or upload files in Question 29.
28. Are you willing to answer follow-up questions for this synthesis?
( ) Yes
( ) No
If “No,” is there an alternative contact? If so, please provide contact information.
7. Upload Files
29. This question may be used to upload up to five relevant files (up to 10 megabytes per file). Addi-
tional files may be e-mailed to Henry Russell at henry@hgrconcrete.com.
8. Review
Here is a review of the entire questionnaire and any responses you have made. You may print using
“control p.”
9. Thank You!
Thank you for taking our survey. Your response is very important to us. If you have any questions or com-
ments, please feel free to contact Henry Russell at:
• E-mail: henry@hgrconcrete.com
• Phone: 847-998-9137
• Mailing address: 720 Coronet Road, Glenview, IL 60025

88
Appendix B
Summary of Responses to Survey Questionnaire
This appendix contains a summary of the responses to the questionnaire. Only those agencies that submitted
responses to the questions are listed.
1. Introduction
Responses to the survey were received from the following U.S. highway agencies and Canadian Provinces:
U.S. States
Alabama New Hampshire
Alaska New Jersey
Arizona New Mexico
Arkansas New York
California North Carolina
Colorado North Dakota
Delaware Oklahoma
Florida Oregon
Illinois Pennsylvania
Iowa Rhode Island
Kansas South Dakota
Louisiana Tennessee
Maine Texas
Massachusetts Utah
Michigan Vermont
Minnesota Virginia
Mississippi Washington
Missouri Wisconsin
Montana Wyoming
Nevada
Canadian Provinces
Alberta Prince Edward Island
Manitoba Saskatchewan
Ontario Yukon
2. General
on bridges with precast, prestressed concrete beams? If your agency does not use a particular system,
check Not Applicable.
Number of Agencies
Type of Concrete Cracking Not
Never Infrequently Frequently Always Unknown
Applicable
with removable formwork 1 7 22 4 2 9
with stay-in-place metal forms 0 9 13 2 1 19
precast concrete deck panels 0 5 10 4 4 21
connections in full-depth precast concrete 1 13 4 1 4 22
deck panels
Cracking in the cast-in-place concrete decks
above the longitudinal connections in 0 12 12 6 3 12
adjacent box beam or slab beam bridges
Cracking in the longitudinal connections
between adjacent box beam or slab beam
0 10 10 2 4 18
bridges when a cast-in-place topping is not
used
Vertical cracks in pretensioned concrete
beams prior to transfer of prestressing force 10 22 1 1 8 2
End splitting cracks in prestressed concrete
beams 9 24 4 3 5 0

89
2. Which of the following types of concrete cracking has your agency experienced in the past
five years on bridges with steel beams? If your agency does not use a particular system, check
Not Applicable.
Number of Agencies
Type of Concrete Cracking
Not
Applicable
0 8 23 6 0 8
with stay-in-place metal forms 0 11 15 2 1 15
0 4 6 5 3 27
connections in full-depth precast concrete 1 9 4 0 2 28
deck panels
on bridges with concrete or steel beams?
Number of Agencies
Type of Concrete Cracking
Not
Applicable
Cracking in non-prestressed concrete beams 1 10 8 1 2 23
Cracking in pier caps 5 26 10 1 2 1
Cracking in columns or abutments 6 29 6 1 2 1
Cracking in pile caps 5 27 5 2 5 1
4. What lessons has your agency learned about controlling concrete cracking? Specific case studies
would be useful for the synthesis. Please list any reports or attach files in Question 29.
Agency Lessons Learned

Alaska Caution must be taken to not over-heat concrete during cold weather concreting operations or
cracking may occur.
California Caltrans has determined that, when a shrinkage reducing admixture is used and 28-day shrinkage is
limited to 0.032 (measured by AASHTO T-160 with 4×4 prism), deck cracking from dry shrinkage
can be eliminated or significantly reduced and that polyolefin fibers and good misting practices
prevent plastic shrinkage cracks so that longer term drying shrinkage performance can be evaluated.
Colorado Better cure times, use of fibers in slope paving and sidewalks. for case studies check our
website/library/research/find topics alphabetical
Delaware Mix qualification for ASR mitigation.
Florida FDOT current policy for crack control in pier caps and columns is a 24 ksi upper limit under Service
III. Attached paper shows theoretically inconsistent crack widths with this approach. The change
suggested by this paper has not been implemented. There is internal discussion on whether or not to
adopt this new approach.
Iowa Concrete cracking is not controlled by the type of reinforcing used. Cracking is controlled by using
proper curing methods and concrete mixes. Nothing will eliminate cracking in concrete. Corrosion
resistant reinforcing helps prevent corrosion induced cracking.
Kansas The majority of our cracking appears related to drying shrinkage, so limiting the paste and going
with an increased curing period (14 days) has reduced cracking. Paste content is indirectly controlled
through permeability.
Louisiana Concrete curing must be done properly as per our concrete construction specifications.
Maine The importance of wet curing. Timely application of wet curing.
Missouri Modified B-2 concrete to reduce cement content.
New Hampshire All concrete cracks
New Mexico Control of conditions to prevent plastic shrinkage cracking has helped.
New York Cracking generally happens in concrete construction mainly due to restrained shrinkage and thermal
effects. Controlling crack widths using appropriate reinforcement, along with sealing of cracked
concrete with penetrating type sealers and/or healer sealer application can reduce the negative
effects on the durability of reinforced concrete exposed to adverse environments. NYDOT also has
recently completed a study on the use of internal curing high performance concrete for CIP concrete
decks. The study found that internal curing concrete is beneficial in reducing deck cracking.

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Agency Lessons Learned

North Dakota Member of Crack Free Bridge Deck Pooled Fund. Research conclusions are available.
Oklahoma ODOT participated in the University of Kansas pooled research on crack free bridge decks
http://www.concretebridgeviews.com/i78/Article2.php
Oregon OSU State Research Report 728. This research developed shrinkage limits to reduce deck shrinkage.
The limits were implemented in 2016. Anecdotal research and trial batching has determined that
concrete fibers help control cracking.
Pennsylvania A Pro Team was assembled including members from all across the state for the purpose of
controlling concrete deck cracking. A pilot program was launched for 2015 including bridge decks
all across the state. This included modifications from the standard specifications for deck concrete
including reducing the maximum cementitious, shrinkage and permeability. The specifications are
attached as well as the interim report created for FHWA.
Rhode Island Most cracking is related to plastic or prying shrinkage and can be addressed by mix design and
curing. Don’t have solution for reported cracking.
South Dakota There are many factors that can influence concrete bridge deck cracking. As of yet the right
combination of materials, placement and curing methods has not been identified to prevent/control
the cracking in SDDOT bridge decks.
Tennessee Place additional re-steel in the negative moment region of the deck seems to help control cracking.
Utah Contact the UDOT Materials Division
Virginia Reduce Cement content to minimize total water volume (w/c ratio stays at .45). Add shrinkage
reducing admixture. Both reduce drying shrinkage cracks
Washington Using performance-based mix has reduced deck cracking on concrete bridges.
Wisconsin WHRP Project 0092-15-01 Precast/Prestressed Concrete Bridge Girder Cracking Phase II is
expected to be completed in 06/2016.
Alberta Mix designs, curing requirements, and construction detailing are critical specification considerations
to reduction potential for cracking. Regardless of the girder type or deck system used the potential
for deck cracking exists. System restraints result in conditions for cracking to occur. Alberta
Transportation has required shrinkage testing on Class HPC concrete use for bridge decks and an
evaluation of the data has been completed. The intent of the evaluation was to develop shrinkage
performance requirements.
Ontario Adequate curing (i.e., carry out curing in strict accordance with specification). MTO requires wet
curing for all structural concrete. Use of retarder to maintain bridge deck concrete in plastic state
until all concrete is placed. Use of pour sequences on long structures. Use of higher strength mixes
and high performance concrete, including self-consolidating concretes, requires even more careful
attention to curing.
Prince Edward We no longer permit the use of curing compounds and specified a full seven day continuously wet
Island cure. This has mitigated a lot of cracking; however, it hasn’t eliminated all of it.
Saskatchewan Proper moist curing at the time of concrete placement. Adjustment of mix design to reduce cracking
and shrinkage.
3. BRIDGE DECKS (canadian participants go to question 6.)
5. Does your agency use Article 5.7.3.4—Control of Cracking by Distribution of Reinforcement of the
AASHTO LRFD Bridge Design Specifications, Seventh Edition to determine maximum spacing of
reinforcement in bridge decks?
Yes with no changes: 26 U.S. agencies

Yes with modifications: 8 U.S. agencies
No: 4 U.S. agencies
If “Yes” or “Yes with modifications,” what value of the exposure factor, γe, does your agency use?
U.S. Agency Modification

Alaska 0.75 in most cases
Arizona 0.75
Arkansas 1
California 0.75
Florida As per SDG 4.1.8 or 3.10
Kansas 1.00 bottom steel, 0.75 top steel
Louisiana We have defined the Class 2 exposure conditions as per our specific La. map in our bridge manual.
Massachusetts 0.75
Missouri 0.75 for Class 2 exposure condition
Montana The conservative one in the code.
New Hampshire 0.75 for Class 2 Exposure condition
New York Designer is to determine the value based on the exposure condition and appearance requirements.
Oklahoma 0.75
Oregon For bridge decks, exposure factor = 1.0; for other elements, exposure factor = 1.0 for moderate
exposure, 0.75 for severe exposure (deicing chemicals, corrosive environment, etc.)
Pennsylvania 1.0 for exposure 1, 0.75 for exposure 2. The same as AASHTO.
Rhode Island 1.0 for Class 1, 0.75 for class 2
South Dakota 1.0 for box culverts & substructures; 0.75 for bridge decks
Tennessee Exposure factor = 0.88 (corresponds to a crack width of 0.015 mm)
Utah See the UDOT Structures Design and Detailing Manual
http://www.udot.utah.gov/main/f?p=100:pg:0:::1:T,V:1730.
Wisconsin 0.75
Wyoming 1.0 Class I exposure

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Florida Decks made continuous (link slabs) have supplementary reinforcing. See SDG 3.10, 4.1.8, 4.2.4,
4.2.6 & 4.2.8 for additional modifications.
Iowa IDOT uses the Z-check rules in the AASHTO LRFD Specs prior to the 2005 Interims.
Kansas Max cover for equations of 2 in., real cover 3 in.
Louisiana Max. value of dc shall be 2 inches plus the radius of the flexural reinforcement closest to the tension
fiber.
Maine Maine DOT’s Bridge Design Guide has standardized deck designs and Article 5.7.3.4 is rarely used
on most designs.
Massachusetts In addition, the quantity of steel was checked against the recommended minimum amounts
identified in a study* initiated by the Indiana Department of Transportation (INDOT). This study
recommends additional reinforcement above current practice to control transverse crack widths in
concrete decks. It provides a formula for calculating a minimum total amount of longitudinal
reinforcement in the section. *Frosch, R.J., D.T. Blackman, and R.D. Radabaugh, “Investigation of
Bridge Deck Cracking in Various Bridge Superstructure Systems, ” Joint Transportation Research
Program, FHWA/IN/JTRP-2002/2.5, 160 pp.
Oregon We limit compressive stress in concrete at service limit state due to positive bending moment
between girders to 0.4 f'c. We limit bar spacing in bridge decks to 8" maximum. We limit rebar size
in bridge decks to be smaller than or equal to #6 bars.
Pennsylvania The following shall replace the definition of dc in A5.7.3.4. dc = thickness of concrete cover
measured from extreme tension fiber to center of the flexural reinforcement located closest thereto
(in.). The (½ in.) wearing surface for deck slab, top and bottom slab of box culvert and (1 in.) extra
cover provided to account for uneven ground level of footing bottom mat reinforcement and bottom
slab of box culverts, shall not be included. The following shall supplement the third paragraph of
A5.7.3.4. Class 1 applies to all reinforced concrete members except precast and cast-in-place box
culverts, segmental construction and for the specific conditions defined under Class 2. Class 2
exposure also applies to precast and cast-in-place box culverts. The following shall replace the
fourth paragraph of A5.7.3.4. In the computation of dc, the actual concrete cover thickness is to be
used except in deck slabs, box culvert slabs and footings as defined in dc.
Rhode Island Redistribution percentage in terms of c/de ratio
Utah http://www.udot.utah.gov/main/f?p=100:pg:0:::1:T,V:1730.
6. What strategies does your agency currently use to minimize cracking in full-depth, cast-in-place
No. of
Responses
Strategy
Yes No
None 2 19
Specify minimum cementitious materials content 23 16
Specify maximum cementitious materials content 20 19
Specify minimum concrete compressive strength 34 4
Specify maximum concrete compressive strength 4 35
Specify a ratio between 7- and 28-day compressive strengths 3 35
Specify minimum concrete temperature at placement 34 6
Specify maximum concrete temperature at placement 37 4
Specify maximum concrete temperature during curing 23 15
Specify maximum water-cementitious materials ratio 39 2
Specify maximum slump 36 5
Specify maximum water content 20 18
Specify the use of a shrinkage-reducing admixture 9 30
Specify the use of a shrinkage-compensating concrete 6 32
Specify the use of fibers 10 30
Require use of the ACI surface evaporation nomogram 25 15
Require wind breaks during concrete placement 15 24
Require evaporation retardants 13 26
Specify internal curing 4 34
Require fogging during placement when evaporation rates are high 27 13
Specify a minimum wet curing period 40 2
Other 11 12
If “Other” or only used under special circumstances, please list.

Agency Other Strategy or Special Use
Arkansas ACI nomograph use and precautions are recommended in internal Resident Engineers ’ Manual. 6%
lithium silicate curing compound and sealant is allowed as contractor substitution for curing
compound and wet cure.
Florida SRAs and fibers are used for special applications. Evaporation retarders can be used at the option of
the contractor. Seven-day wet curing is required for bridge decks.
Illinois Though we do not specify shrinkage compensating materials, shrinkage reducing admixtures, or
internal curing, we have developed special provisions for such items to be used at the discretion of
our Districts. We are currently researching the benefits and optimization potential of all three items,
and have built 2 Type K decks and 2 SRA decks in recent years. We have just released our internal
curing specs and hope to have a District or two try it soon. We are also trying a textured epoxy-
coated rebar that “bonds” to the concrete like black bar.

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Agency Other Strategy or Special Use

Iowa Require retarding admixture to maintain concrete plasticity during beam/girder deflection when
continuous placement.
Kansas A minimum strength and cement content is not intended to limit cracking.
Louisiana Total air content, percent by volume.
New Hampshire NHDOT approves a contractor submitted QC plan to eval uate and control evaporation.
New York NYSDOT is prescribing a standard High-Performance Concrete mix for bridge decks. Internal
curing has been tried on a limited number of decks during last five years. Based on the observed
beneficial effects NYSDOT is planning to expand the use of internal curing concrete for deck
applications.
Oklahoma For bridge decks, we require 7 day’s wet cure followed by 7 days of membrane cure.
Rhode Island Have a required maximum shrinkage for some mix designs, based on class of concrete.
Texas Three of the 25 districts in TxDOT specify micro-fibers to reduce plastic shrinkage cracking.
Utah Refer to the UDOT Specifications for Structural Concrete
Wyoming Take action to reduce evaporation such as provide shade, use ice, or other cooling methods and
provide wind barriers. Evaporation retardants and fogging are not required but both have been used
and are accepted methods when proposed.
most effective?
Agency Strategy
California Limiting drying shrinkage and mandating shrinkage reducing admixture paired with good misting
and polyolefin fibers to prevent plastic cracking
Florida Currently, 7-day wet curing of decks, then curing compound. We are researching the use of
internally cured concrete for deck applications as well.
Iowa 1. Evaporation control
2. Reduction in portland cement
3. Requiring retarding admixture for continuous placements
Kansas Increased curing period (started within 15 min.) and reduction of paste content.
Louisiana Proper curing.
Maine Hard to say what has been most effective since we are still seeing cracking in full depth cast in place
bridge decks.
Massachusetts To specify minimum wet cure period and to require fogging during concrete placement
Michigan Night casting
Minnesota Fibers, and wet cure
Missouri Modified B-2 concrete and extend curing period to minimum 7 days
New Hampshire NHDOT mainly places a torch applied waterproof membrane over its concrete decks and 2.5"
asphalt wearing surface.
New Jersey Wet curing
New Mexico Wind break, fogging system, staggering of top and bottom transverse bars by one-half bar spacing.
New York Temperature control of concrete at the time of placement, application of curing method without
significant delay and the use of internal curing. Avoiding late season placements which will need
addition of external heat also appears to be beneficial. Staged placement of decks, most of the
positive moment areas first and the negative areas after 72 hours appears to be beneficial.
North Dakota Wet cure applied within 15 minutes of paver placement. Keep wet continuous throughout curing
period.
Oklahoma We did an experimental deck (research is still preliminary) with pulpcure: Pulpcure was developed
at Oklahoma State University under Dr. Ley. Pulpcure is made up of recycled newspaper, water, and
chemical admixtures to help it flow while staying cohesive. It can be applied with minimal labor.
The raw materials are pumped to the surface of the concrete and evenly applied. In the laboratory
and on field applications, pulpcure has shown the ability to hold the moisture for longer periods than
saturated wet burlap. The challenge has been to find a good way to apply it to a 40' wide bridge deck
in a timely manner without damaging the deck surface. The material is biodegradable.
Oregon Use of fibers. Keep concrete strength around 4000 psi.
Pennsylvania Reducing the maximum cementitious, optimizing aggregates to reduce the paste content, setting
limits on permeability and shrinkage.
Rhode Island All the above “yes” answers. Reduction of silica fume in the mix.
Virginia 1. Limits on total paste; 2. Shrinkage reducing admixtures; 3. Allow lower compressive strength in
decks; 4. Allow contractor additional time before traffic is applied to deck.
Wisconsin Immediate fogging and application of wet burlap; Seven-day wet cure.
Wyoming Monitoring evaporation rates with max at 0.2 lb/sf/hr, max w/c ratio at 0.45, timely curing. Looking
at shrinkage-reducing admixtures.
Alberta Appropriate mix design and use of cementing materials, wet curing requirements. Use of combined
supplementary cementing materials (fly-ash & silica fume) to reduce shrinkage potential and slow
hydration processes.
Ontario As above. Require placement of wet burlap curing within 2–4 m of finishing machine (on bridge
decks) and within 2–4 m of finishing operation for other elements. Plastic placed over burlap and
soaker hoses to maintain burlap in wet condition over 4-day (or 7-day) curing period. Fog misting
required for high performance concretes, during placement in bridge decks. For all bridge decks and
for large (>1 thick) elements, require measurement of concrete temperature by thermocouples and
data logger at centroid and extremities during curing period, to verify temperature limits are met.
Prince Edward Minimum wet curing period.
Island
Saskatchewan Fogging and immediate placement of wet cure blankets.
Yukon By following all concrete quality control measures.

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least effective?
Agency Strategy
Arkansas Unknown because unequal application of specifications and substitutions create variable risk of
cracking. However, increases in cracking roughly tracks larger continuous pours requested by
contractors and longer spans.
Florida No curing at all. Curing is a necessity here in Florida due to our high temperatures and windy
conditions near the coast line.
Illinois What we’re currently doing doesn’t appear to be very effective.
Iowa Use of extended wet curing periods.
Kansas Evaporation retardants, at best belt and suspenders with a good curing process. At worst, more water
added to the surface.
Louisiana Contractor not curing properly as per our specifications.
Maine Refer to #7.
Michigan Continuous decks for live loads.
New Jersey Not providing proper wet curing.
New York Use of set retarding admixtures to enable large single pour of multi-span bridge decks appears to be
of little value.
Oklahoma Wet curing is preferred to curing compounds.
Oregon Limit maximum slump. Require wind breaks during placement.
Pennsylvania The pilot program included a provision that fogging apparatus be used regardless of evaporation
rate. This became a problem because at times the water did not atomize and ponded on the fresh
concrete creating a slurry.
Rhode Island Use of fibers and shrinkage compensating admixtures.
Virginia 1. Making contractor open deck to traffic quickly. This makes them add cement and therefore water,
making the deck more likely to crack.
2. Emphasizing strength over durability.
Wisconsin Fibers
Alberta Fogging systems. Effective fogging systems are cost prohibitive and contractors typically try to
utilize portable pressure washers which are ineffective and poorly implemented in the majority of
applications where used. Fogging systems were specified for many years but discontinued in lieu of
placement of evaporation reducers prior to implementation of continuous surface wet cure systems.
Ontario Currently we have ceased use of high performance concretes in bridge decks due to problems with
cracking in some decks; cracking does not occur in all decks, but reasons for cracking are not clear.
Considering use of shrinkage testing to prequalify high performance and high strength mixes for use
in bridge decks. Use of saturated lightweight aggregate for internal curing considered but does not
appear to be practical as a standard approach.
Prince Edward Curing compounds.
Island
9. What is the frequency of use of the following cements in your agency’s concrete bridge decks?
Number of Responses
Material
Never Sometimes Often Always
AASHTO M 85 Type I and IA 7 4 13 9
AASHTO M 85 Type II and IIA 3 6 13 11
AASHTO M 85 Type II(MH) and
19 3 6 1
II(MH)A
AASHTO M 85 Type III and IA 23 7 1 1
AASHTO M 85 Type IV 32 0 0 0
AASHTO M 85 Type V 29 2 1 0
AASHTO M 240 22 5 3 1
ASTM C1157 23 3 2 1
10. What is the frequency of use of the following supplementary cementitious materials in your agency’s
Number of Responses
Material
Fly ash Class C 11 11 13 3
Fly ash Class F 5 11 17 6
Pozzolan Class N 26 8 2 0
Silica fume 11 16 9 5
Ground-granulated
12 10 15 1
blast-furnace slag
Other 17 1 0 1
Other listed materials were metakaolin, and fly ash and lithium if reactive aggregate is used.

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11. What is the frequency of use of the following admixtures for cast-in-place concrete bridge decks?
Number of Responses
Admixture
AASHTO M 194 Type A—Water-reducing admixtures 2 7 15 14
AASHTO M 194 Type B—Retarding admixtures 4 20 10 3
AASHTO M 194 Type C—Accelerating admixtures 19 15 2 1
5 18 11 3
admixtures
21 14 2 1
admixtures
AASHTO M 194 Type F—High range water-reducing
8 12 13 5
admixtures
16 15 5 2
Corrosion inhibitors 25 11 2 1
Shrinkage-reducing admixtures 21 13 2 2
Expansive cement or components 30 8 0 0
12. What length of wet curing does your agency currently specify for cast-in-place concrete bridge decks?
Number of Responses
None 3 days 7 days 14 days Other

1 3 20 11 8
Other lengths of wet curing were 4, 5, 8, and 10 days. One agency reported using curing compound.
13. How is wet curing achieved?

Agency Method
Alaska Heavy burlap or quilted cotton blankets are most often used. Infrequently, full wetting and
saturation with sprayers or perforated hoses are used.
Arkansas Burlap-polyethylene mats or burlap covered with approved sheeting materials. Burlap
maintained continuously and thoroughly wet for 7 days, typically with soaker hoses.
Delaware Plastic, burlap, hoses
Illinois Wetted cotton mats or cellulose polyethylene blankets.
Iowa Curing Concrete Decks. Use burlap with sufficient water that is prewetted by fully saturating,
stockpiling to drain, and covering with plastic to maintain wetness prior to placement, to
prevent absorption of moisture from the concrete surface. Keep the burlap wet.
1. Place the first layer of prewetted burlap in the following manner: a. Interstate and Primary
Projects. Place on the concrete within 10 minutes after final finishing. b. Other Projects.
Immediately after final finishing and grooving, cover the area finished with white pigmented
curing compound meeting requirements of Article 4105.05 applied at a maximum rate of
135 square feet per gallon. Place the first layer of prewetted burlap on the concrete within
30 minutes after the concrete has been finished and grooved. Burlap placement beyond
30 minutes may be allowed, up to an additional 30 minutes, if approved by the Engineer based
upon environmental conditions at time of deck placement.
2. As soon as practical, but no later than 2 hours after placing the first layer, place a second
layer of prewetted burlap on the deck.
3. Apply water to the burlap covering for a period of 4 calendar days. Use a pressure
sprinkling system that is effective in keeping the burlap wet during the moist curing period.
The system may be interrupted only to replenish the water supply, during periods of natural
moisture, or during construction contiguous to the concrete being cured. The Engineer may
approve interruptions for periods longer than 4 hours on the basis of the method for keeping
the concrete moist.
4. Maintain continuous contact, except as noted above, between all parts of the concrete deck
and the burlap during the 4 calendar day moist curing period.
5. On concrete decks placed after October 1 and prior to April 1, after 20 hours of the
application of water, the Contractor may substitute the application of a moisture proof plastic
film no less than 3.4 mils thick over the wet burlap in lieu of applying water. Maintain
intimate contact between the surface of the concrete, the burlap, and the plastic film.
Kansas Burlap, soaker hoses, plastic
Maine Soaker hoses, wet burlap, and plastic sheets or insulated blankets
Massachusetts Wet burlap
Michigan Burlap, soaker hose, and plastic sheeting
Minnesota Pre-wetted burlap within 30 minutes, soaker hoses, white poly covering
Mississippi We do not wet cure.
Missouri With wet mat. Plastic cover over wet burlap for curing low slump or silica fume concrete after
24 hours of continuously keeping wet.
Montana Presoaked burlap, soaker hoses, plastic
Nevada Soaker hoses and burlap covered in plastic or wet curing blankets.

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Agency Method
New Hampshire Wet burlap
New Jersey Wet burlap and white polyethylene sheeting
New York 14 day’s burlap covered constantly wet. Last 7 days curing covers permitted to replace burlap.
North Dakota Burlap and water
Oklahoma Fogging, followed by the application of two layers of wet burlap, wet burlap is covered with
white polyethylene film and soaker hoses are used to keep the burlap wet at the end of 7 days,
the curing membrane is applied.
Oregon Require wind breaks when evaporation rate reaches a specified limit. Apply fog spray for all
placements. Cover wet concrete with saturated wet burlap or non-woven, needle punched
polypropylene fabric curing blanket within a maximum time limit. Provide soaker hoses.
Place a layer of polyethylene film over the covering and soaker hoses.
Pennsylvania Wetting the concrete deck and placing wet burlap all over the deck surface.
Rhode Island Wet burlap with plastic or fogging
South Dakota Typically, with wet burlap/curing blankets and poly sheeting.
Tennessee a) place damp burlap over slab; b) apply a mist spray over the cover and thoroughly wet with a
continuous soaker hose system for 120 hours.
Texas Wet cotton mats covered with plastic or other wet blanket system. Must keep wet.
Utah Refer to the UDOT Specifications—Structural Concrete or Contact the UDOT Materials
Division
Vermont Wet burlap typically
Washington Fogging and burlap
Wisconsin 502.3.8.2.3 Decks (1) For structures under 100 feet in length, cure the concrete in decks,
medians, and sidewalks for at least 7 days with polyethylene-coated burlap or other coated
material conforming to 501.2.9. As soon as the concrete sets sufficiently to support the
covering, place the coated burlap with the coated side up; or perform an initial cure of the
concrete by using wetted burlap for at least 12 hours and then apply the coated burlap to a
thoroughly wetted concrete surface. Place each strip or sheet of coated burlap so that it
overlaps the preceding sheet by at least 12 inches. Secure the coated burlap covering in place.
Ensure adequate moisture is present on the surface of the floor, wearing surfaces, or sidewalks
beneath the curing material for the 7-day curing period. (2) For Structures 100 feet or greater
in length, cure the concrete in decks, medians, and sidewalks by the following method. Begin
curing the horizontal concrete surfaces by fogging within 15 minutes of finishing and tining.
Apply the fog or fine water spray so that no water marks result and no mortar washes from the
concrete surface. Keep the concrete surface continuously wet by fogging until applying the
burlap strips to the finished concrete. Wet the burlap immediately after placement. During the
first day, until placing the soaker hose system, keep the burlap continuously wet. Through the
remainder of the curing period, keep the burlap continuously wet with soaker hoses hooked up
to a continuous water source. Inspect the burlap on a daily basis to ensure that the entire
surface is moist. If necessary, alter the soaker hose system as needed to ensure the entire
surface is moist. Do not use white polyethylene sheeting or plastic coated burlap blankets.
Continue moist curing at least 7 days.
Wyoming Burlap or polyethylene sheeting continuously damp using fogging methods.
Alberta Two layers of filter fabric or 1 layer of filter fabric and 1 layer of thinner fabric with
perforated poly.
Manitoba Blanketing and wetting
Ontario Burlap presoaked for 24 hours prior to use. Soaker hoses placed on burlap to operate
throughout curing period. Plastic placed over all to reduce evaporation. Fogging for silica
fume concretes during placement.
Prince Edward Contractors have a storage tank of water on site connected to a series of perforated hoses
Island across the deck top overlaid onto filter fabric or burlap. The water runs continuously for 7
days.
Saskatchewan Curing blankets and sprinklers
Yukon Using soaked wet burlaps
14. Does your agency specify epoxy-coated reinforcement for concrete decks?
U.S. agencies only. Canadian agencies do not use epoxy-coated reinforcement.
No. of
Responses
Reinforcement
Yes No
Top layer 33 5
Bottom layer 3 5
Girder reinforcement projecting into the deck 23 13
15. What types of reinforcement with metallic coatings has your agency used in cast-in-place concrete
bridge decks?
None: 19 agencies
Zinc coated: 19 agencies
Stainless steel coated: 13 agencies
Other: 3 agencies but did not list the type.
Explain any effect of their use on cracking.

96
State Effect
California None
Iowa We have only built a handful of bridge with galvanized reinforcing. Most of the bridges were
built in the 1970s. Deck deterioration took longer to initiate, but deck cracking wasn’t
necessarily reduced compared to a conventionally reinforced deck.
Kansas None noted
Maine No evidence that a reduction of cracking has resulted. Use has been for increased corrosion
protection.
Missouri Not aware of
New Jersey None observed
New Mexico Similar to epoxy coating. Rarely used.
New York There is no obvious difference in cracking when metallic reinforcement is used.
North Dakota Used once. No idea on effect of cracking.
Pennsylvania Cracking is more of a function of the cementitious properties than rebar coating.
Rhode Island Unknown
Vermont We see no difference based on coating.
Virginia No known affect
Wyoming Zinc coated used on one bridge in the top mat only.
Alberta Not measured
Ontario No apparent impact; these materials were used on a very limited basis and are not currently in
use.
Saskatchewan No difference than black steel
16. Has your agency used solid stainless steel reinforcement in cast-in-place concrete bridge decks?
Yes: 18 agencies
No: 24 agencies
Agency Effect
California No effect
Colorado No data
Kansas None noted
Minnesota No initial change
Montana One time about 16 years ago
New Jersey No difference
New Mexico Similar to epoxy coating. Rarely used.
New York No obvious difference
Oregon SS is used in coastal environments where temperature and humidity are relatively constant, so
deck cracking is minimized due to these environmental conditions. Cracking is minimal minor
tight cracks, less than in other portions of Oregon.
South Dakota No difference in deck cracking was noted.
Vermont No effect if cover is maintained. We are trying some projects to reduce cover to get
reinforcement closer to the top surface of the deck when solid stainless is used.
Virginia No known effect
Wisconsin No effect
Ontario No apparent impact. Not sure that this has been evaluated comprehensively.
Saskatchewan No difference in cracking than black steel
17. Has your agency used fiber-reinforced polymer (FRP) reinforcement in cast-in-place concrete
bridge decks?
Yes: 17 agencies
No: 25 agencies
If Yes, how did its use affect deck cracking?
Agency Effect
California Prevents plastic shrinkage cracks and holds cracks tighter if they do form.
Florida Proposed on Halls River Bridge Replacement for letting 6/15/16.
Kansas None noted
Maine Too early to tell. Just started to use it experimentally.
Minnesota Project will be let in the summer of 2016 so no results yet.
Missouri Not known
New Hampshire Greatly reduced cracking
Oregon Similar to SS, we use it only in coastal environments where we experience much less deck
cracking.
Utah GFRP
Vermont Not enough data to tell.
Virginia No known effect
Ontario Used to limited extent in decks. Not aware of any apparent impact, but not sure how
exhaustive the investigation has been.
Prince Edward Initially there was some increase in the amount of cracking; however, as time and experience
Island progressed, we see no net effect of cracking increase or decrease with the use of FRP bars
versus black steel.
Yukon It helped in preventing the deck cracking.

97
18. Has your agency used ASTM A1035 reinforcement in bridge decks based on a yield strength of
100 ksi for design?
Yes: 3 agencies
No: 39 agencies
Agency Effect
Florida As of January 1, 2016, now allowed by FDOT Structures Manual. We have a bridge
constructed with MMFX-II; however, it was not based on the design yield strength. Rather it
was a direct replacement of conventional steel. There are spans with conventional and
MMFX and both are performing similarly at this stage. See attachment for more details.
Oklahoma No data available
Virginia Not sure
Yukon Used CSA approved amount
4. PRESTRESSED CONCRETE BEAMS (Canadian participants go to Question 21)
19. Does your agency use Article 5.10.10.1—Splitting Resistance of the AASHTO LRFD Bridge
Design Specifications Seventh Edition to design the splitting reinforcement at the ends of beams?
Yes with no modifications: 23 U.S. agencies
No: 7 U.S. agencies
Agency Modification
Florida Have specified areas of splitting reinforcing for a maximum bonded prestress force in
standard beam shapes (See SDG 4.3.1.D). Use a minimum of 10 in. for h/4.
Illinois Refer to “Page 3-214” & “Page 3-215” of our Bridge Manual, as well as Figure 29 of ABD
Memo 15.2.
Minnesota Vertical reinforcement H/4 is sometimes increased. To fit the required amount of steel in the
ends and still allow the concrete to flow between the vertical bars.
Oklahoma In order to keep cracks less than 0.012", one of our fabricators is using additional steel
exceeding the requirements of 5.10.10.1, this modification is being done in the shop
drawings.
Pennsylvania The following shall replace A5.10.10.1. The splitting resistance of pretensioned anchorage
zones provided by vertical reinforcement in the ends of pretensioned beams at the service
limit state shall be taken as: Pr = fsAs (5.10.10.1-1) where: f s = stress in steel not exceeding
20 ksi As = total area of vertical reinforcement placed near the ends of the beam at maximum
spacing of 3 in. End blocks shall be investigated to help in reducing splitting stresses for
prestressed beams or pier caps with forces in excess of 1800 kips. Closely spaced grids for
members with forces in excess of 1800 kips shall have the grid anchored. The reinforcement
for the end blocks shall be shown on the shop drawings and shall be in accordance with
recommendations of the anchorage fabricator.
Utah Refer to the UDOT Structures Design and Detailing Manual
Washington Spread bars beyond h/4 as needed
20. Does your agency use Article 5.10.10.2—Confinement Reinforcement of the AASHTO LRFD
Bridge Design Specifications to design the confinement reinforcement at the ends of beams?
Yes with no modifications: 29 U.S. agencies
No: 3 U.S. agencies

Florida Use tighter spacing beam ends, and do not always extend the placement to the full 1.5d.
Missouri Provide 4 pairs of reinforcement (3 spaces @ about 3 1/ in.) in the end of prestressed girders. Extend
the confinement reinforcement for the full length of girders. Increase confinement reinforcement
spacing where not needed.
Pennsylvania The following shall supplement A5.10.10.2. For prestressed beams, additional confinement
reinforcement shall extend from each end of the beam for ¹⁄³ of the span length. The additional
confinement reinforcement shall not be less than No. 4 deformed bars and match with vertical stirrups
with maximum spacing of 21 in.
Utah Refer to the UDOT Structures Design and Detailing Manual
5. Substructures
21. Does your agency use the same crack control criteria for substructures and superstructures?
Yes: 28 agencies
No: 11 agencies

98
If “No,” what criteria are used for substructures?
Agency Criteria
Florida See SDG 3.10.A vs. SDG 4.1.8.
Illinois Lower minimum cementitious content, lower minimum strengths, different allowable
aggregate gradations, more options for curing, and we are not looking to try SRAs or
shrinkage compensating materials in substructure concrete.
Iowa We follow Article 5.7.3.4 for substructures.
Minnesota Exposure factor gamma sub e is different. For Slabs and Pier Caps the factor is 0.75 and for
all other situations we use 1.0.
Oregon We have the same criteria as those required for superstructures, except for bridge decks we
have more requirements as described in questions 5 & 7.
Rhode Island Mostly Mass concrete protocols. Note that many of the mix designs are used throughout.
South Dakota Gamma sub “e” = 1.0
Alberta CAN/CSA S6—Canadian Highway Bridge Design Code
Ontario Per Canadian Highway Bridge Design Code (CSA S6 2014)
Prince Edward Only difference is curing period. Still a full wet cure; however, only for 3 days as opposed
Island to 7.
22. If your agency has experienced cracking in pier caps, please describe the type of pier cap
(rectangular, inverted tee, hammerhead, etc.) and type of cracking (flexure, shear, tempera-
ture, etc.)?
Agency Type of Pier Cap and Type of Cracking

Alaska Cracking associated with over-heating of enclosures during cold weather concreting
operations has occurred.
California Shrinkage
Colorado Shrinkage
Florida 1. Hammerhead flexure—now limit 24 ksi reinforcing stress under Service III;
2. Straddle Bent Cap shear;
Iowa Rectangular pier caps typically show signs of minor flexure cracking in positive and
negative bending areas. Shear cracking is seldom seen. Cracking of the ends of the cap
under joints is common due to corrosion in the reinforcing. Hammerhead caps seldom have
flexure or shear cracking.
Massachusetts Shrinkage
Minnesota Rectangular temperature
Missouri Rectangular pier cap. Very rare temperature crack found. Shear cracks found in a few
hammerhead piers.
New York Yes, occasionally NYSDOT has experienced cracking in pier caps. Most of these cracks are
temperature and shrinkage related. Flexure cracks at the tops of hammerhead piers with
epoxy coated bars were observed few years ago. NYSDOT is not allowing epoxy coated
bars as top flexure reinforcement for hammerhead piers now.
North Dakota Nothing in the last 5 years
Oklahoma Cracks in new construction are very rare.
Oregon Significant shear cracking has occurred in 1950s—1960s era rectangular caps and
crossbeams that had short longitudinal bar development and large shear steel spacing.
Pennsylvania No cracking in new designs.
Rhode Island Hammerhead
South Dakota Not aware of pier cap cracking
Texas Shear cracking in straddle caps (inverted T and rectangular) cracking in inverted T ledge
(due to older provisions that led to under-reinforcement)
Wyoming Hairline flexure and shear is typical in rectangular/hammerhead pier caps.
Alberta Rectangular, hammerhead, etc. Shrinkage/temperature/flexure/formwork settlement
Manitoba Yes—very infrequent-solid shaft rectangular, associated with temperature. Also having
cracking in shaft on some projects associated with shock; i.e., cold weather.
Ontario Has not been an issue
Prince Edward Hammer head piers. Mainly shear and temperature and/or shrinkage cracking.
Island
Saskatchewan Rectangular, temperature and shrinkage cracks.
23. If your agency has experienced cracking in columns or abutments, please describe the type of
cracking (flexure, shear, temperature, etc.)?
Agency Type of Cracking

Florida Hammerhead column flexure cracks under construction wind loading.
Iowa Cracking in columns due to flexure or shear is uncommon. Cracking usually occurs from
temperature induced cracks that allow the moisture to penetrate the concrete and cause more
severe cracks from corrosion. Abutments normally have vertical cracks that are most likely
shear related.
Minnesota Abutments temperature
Missouri Very rare temperature crack found.

99

New Hampshire We normally have 4" weep holes in our abutments 10' on center and have experienced
vertical shrinkage cracking at those locations.
New York NYSDOT is experiencing some shrinkage and temperature cracking on abutments and wing
walls. These cracks are generally tight and structurally not significant.
North Dakota Nothing in last 5 years
Oklahoma Cracks in new construction are unusual.
Oregon Rare vertical cracking has occurred due to uneven settlement or foundation undermining.
Pennsylvania No cracking in new designs.
Rhode Island Maybe temperature
South Dakota Not aware of column or abutment cracking
Texas Temperature related in columns. Thermal/shrinkage in abutment backwalls.
Wyoming Temperature is common. Some flexure.
Alberta Shrinkage/flexure/temperature/formwork settlement
Manitoba Yes—very infrequently shrinkage
Ontario Some (rare) vertical cracking in wide abutments, but I do not know the details.
Prince Edward Mainly temperature and/or shrinkage cracking
Island
Saskatchewan Longitudinal cracking matching longitudinal rebar.
24. If your agency has experienced cracking in pile caps, please describe the type of cracking (flexure,
shear, temperature, etc.)?
Florida Minor temperature cracking
Iowa Unknown, because most pile caps are buried underground, if you are asking about footing
pile caps.
Missouri No
New York NYSDOT use of pile caps is limited and no significant issues with cracking have been
raised.
North Dakota Nothing in last 5 years
Oklahoma Not aware of cracks in pile caps
Pennsylvania Minor shrinkage cracking in thicker footings.
Rhode Island Temperature maybe. In one case, expected to crack. Rebar used.
South Dakota Not aware of pile cap cracking
Texas Mostly not aware of. On very large pile caps—have seen cracking related to lack of proper
curing.
Wyoming Is this the same as pier caps?
Alberta Shrinkage/temperature/formwork settlement
Manitoba Not usually—very infrequently sometimes occurs on wide abutments or pile caps from
shrinkage.
Prince Edward Mainly temperature and/or shrinkage cracking.
Island
Saskatchewan Not known
6. Research
25. Please list any research in progress by your agency related to concrete cracking.
Agency Research in Progress
Arkansas TRC 1602 Examining the Required Cement Content in Structural Concrete
Florida Mitigation of Cracking in Florida Structural Concrete.
- Use of Lightweight Fine Aggregate for Internal Curing and Control of Cracking in
Concrete.
- Macro Synthetic Fiber Reinforcement for Improved Structural Performance of Concrete
Bridge Girders. This is mainly research to improve pretensioned girder end cracking through
the use of fibers.
Illinois Refer to ICT R27-139 (Phase I report available here; Phase II report available Fall 2016;
Phase III starting Summer/Fall 2016).
Iowa HRB TR-633 Investigation into Shrinkage of High Performance Concrete Used for Iowa
Bridge Decks and Overlays, Phase II - Shrinkage Control & Field Investigation
Kansas Evaluation of internal curing, void-based mix designs and ongoing evaluation of SCMs.
Maine Maine DOT is beginning to look at non shrink additives for cracking control.
New Mexico Research primarily focused on deck cracking in the 1980s and 1990s. Led to procedures
listed previously. Further research in the last decade related primarily to wind breaks and
fogging systems.
North Dakota Member of Crack Free Bridge Deck Pooled fund. Plan on implementing those
specifications
Oklahoma ODOT FFY 2016 SP&R Item Number 2274 “Development of Concrete Mixtures to
Mitigate Bridge Deck Cracking, Validated Using 3D Bridge Deck Surface Evaluations.”
Note that this research is still in the very early stages.
Pennsylvania A pilot program was launched in 2015 specifically for deck cracking. Some tweaks were
made and a 2016 pilot project is in the works.
Texas 16-337: Evaluating Long-Term Durability/Performance of Prestressed Concrete Beam with
Extensive Surface Cracking 16-342: Evaluation of Structural Cracking in Concrete

100
Agency Research in Progress

Utah Contact UDOT Research
Virginia Study of decks cast using special “low cracking deck concrete” specification
Wisconsin WHRP Project 0092-15-01Precast/Prestressed Concrete Bridge Girder Cracking Phase II
Ontario Our agency is funding research at University of Toronto to look at evaluating the cracking
potential of high performance concrete mixes. We would like to be able to prequalify high
performance mixes for use in bridge deck applications, to avoid excessive cracking.
Yukon Cracks on the deck top of floor beams (Pony and Through truss deck structures)
26. Please list any recommendations for future research needs related to concrete cracking.
Agency Research Recommendation
Alaska Specifying permissible crack widths associated with different size reinforcing bars.
Florida Investigate methods for improving the end region cracking in pretensioned girders.
Kansas Expansive admixtures
Maine Cement- and pozzolan-based research could be useful in conjunction with shrinkage-
reducing admixtures
New Mexico Methods for reducing reflective cracking when partial-depth precast deck panels are
employed.
New York NYSDOT is more focused on implementing the findings of research into design and
construction practices.
North Dakota Deck cracking
Oklahoma Pulpcure—bridge deck applications, internal curing and SRA’s appear to have some
potential
Pennsylvania A shrinkage-reducing admixture, further reducing the shrinkage from 500 microstrains to
250.
Rhode Island Some hopefully addressed by NCHRP FY2017 D-03, if accepted
Utah Contact UDOT Materials
Alberta Comparative study of partial depth precast concrete deck panel vs. conventional full depth
cast-in-place deck cracking. Noticeable reduction in crack frequency for partial depth panel
decks with same HPC concrete mix.
Ontario Need more research on behavior of concrete mixes with multiple admixtures, particularly
high performance and self-consolidating concretes. Basic slump and physical property tests
are insufficient to identify suitable mixes for use in highway applications. Need tests to
quantity shrinkage and cracking potential. Further information on role of reinforcement
layout on crack control (or not) is needed, for high strength concrete mixes; there has been
little coordination between designers and materials experts in identifying causes of cracking.
Saskatchewan How to reduce and control vertical cracks in cast in place traffic barriers. On top of a
concrete deck slab.
Yukon Use additional reinforcement or control joints on the center of floor beam to mitigate
cracking.
27. Please list any agency research reports that document the performance in bridges with regard to
control of concrete cracking and are available to be referenced in this synthesis. Case studies are
of particular interest. Please provide links or upload files in Question 29.
Agency Research Report
Arkansas TRC 0603 Curing Practices to Reduce Plastic Shrinkage in Concrete Bridge Decks, 2011 TRC
1002 Evaluation of High Performance Curing Compounds on Freshly Poured Bridge Decks
2012
California Evaluating Proposed Concrete Specifications for the Prevention of Deck Cracking.
Florida Files will be emailed separately. They are not necessarily reports that document the
performance: however, they are reports that relate to research that was conducted to improve
the cracking performance.
Iowa Mass Concrete—http://www.intrans.iastate.edu/research/documents/research-
reports/mass_concrete_i_w_cvr.pdf
http://www.iowadot.gov/research/reports/Year/2014/fullreports/mass_concrete_ii_w_cvr2.pdf
Kansas The University of Kansas has completed several for us: Files are available at the following,
particular reports of interest include SL Report 15-3, SM Report No. 107, ODOT SPR Item
Number 2231, SM Report No. 103, SM Report 94, and SM Report No. 92:
http://iri.ku.edu/reports
North Dakota Crack Free Bridge Deck Pooled Fund Research Final Report
Oregon “The Use of Synthetic Blended Fibers to Reduce Cracking in High Performance Concrete,”
SPR 500-620, Oregon State University, September 2014. “Development of Shrinkage Limits
and Testing Protocols for ODOT High Performance Concrete,” SPR 728, ODOT-OSU,
December 2013.
Pennsylvania A report conducted by Penn State University and an interim report to FHWA is attached.
South Dakota “Optimized Aggregate Gradation for Structural Concrete,” SD2002-02
http://www.sddot.com/business/research/projects/docs/SD2002_02_Final_Report.pdf.
Texas FHWA/TX-12/0-6348-2 Evaluation of Alternative Materials to Control Drying-Shrinkage
Cracking in Concrete Bridge Decks, Report No. 0-4098-4. Author: Kevin Folliard
Utah Contact UDOT Research or visit the UDOT website for research projects
Virginia Upcoming report from the Virginia Transportation Research Council
Washington WSDOT report on evaluation of performance-based concrete mixes for bridge decks.
Ontario I am attaching an internal report completed by MTO several years ago investigating the
cracking of high performance concrete bridge decks (60 MPa, 1000 Coulomb RCP) in
northern Ontario. The investigation showed a correlation between temperature of the concrete
during the first 24–48 hours, and degree of cracking, with mixes that reached higher
temperatures faster exhibiting more cracking. Cracking was not related specifically to mix
design, since mixes with the same parameters cracked in some cases and not in others.
101
Appendix C
Cross Reference Table for AASHTO LRFD Bridge Design Specifications
Eighth Edition 2017 Seventh Edition
5.6.3.3—Minimum Reinforcement 5.7.3.3.2
5.6.7—Control of Cracking by Distribution of Reinforcement 5.7.3.4
5.7.2.5—Minimum Transverse Reinforcement 5.8.2.5
5.7.2.6—Maximum Spacing of Transverse Reinforcement 5.8.2.7
5.8.2.6—Crack Control Reinforcement 5.6.3.6
5.9.4.4.1—Splitting Resistance 5.10.10.1
5.9.4.4.2—Confinement Reinforcement 5.10.10.2
5.10.3.2—Maximum Spacing of Reinforcing Bars 5.10.3.2
5.10.6—Shrinkage and Temperature Reinforcement 5.10.8
5.12.2.3.3d—Longitudinal Construction Joints 5.14.4.3.3d

102
Appendix D
Research Problem Statement
AASHTO STANDING COMMITTEE ON RESEARCH

AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS
NCHRP Problem Statement Outline
I. Problem Number
To be assigned by NCHRP staff.
II. Problem Title
Control of concrete cracking by distribution of reinforcement, including high-strength steel bars,

coated and non-coated bars, and non-metallic reinforcement.
III. Research Problem Statement
Concrete is a quasi-brittle material with a low tensile strength. Applied loadings, deleterious chemical
reactions, and environmental effects can result in the development of tensile stresses in concrete. When
these tensile stresses exceed the concrete tensile strength, the concrete will crack. The extent and size
of cracks have an effect on the performance of the bridge. However, the extent of cracking can be mini-
mized by the proper distribution of reinforcement. The AASHTO LRFD Bridge Design Specifications
has provisions for crack control to assure serviceability, aesthetics, and economy. Article 5.7.3.4, Con-
trol of Cracking by Distribution of Reinforcement, is intended for the distribution of tension reinforce-
ment to control flexural cracking. However, Equation 5.7.3.4-1 was developed to match other existing
equations without any comparison with test data. There are several parameters in the equation such as
bs, dc, ge, and fss that need to be investigated. There are very limited data on crack widths in specimens
having typical deck slab thicknesses and containing high-strength steel bars or non-metallic reinforce-
ment. There is also a question whether coated and non-coated bars should have a different maximum
spacing and concrete cover.
There are also two anomalies associated with the use of Equation 5.7.3.4-1. Firstly, if the concrete
cover is increased to provide better corrosion protection to the reinforcement or to allow for grinding,
the maximum bar spacing is required to be less. Secondly, the equation does not have to be applied to
bridge decks designed by the empirical design method. This method permits a maximum bar spacing
of 18 in., which is not appropriate for crack control.
One of the major concerns of bridge owners is cracking in concrete bridge decks caused by shrinkage
and thermal effects. Although this cracking can be reduced by proper selection of concrete constitu-
ent materials, some cracking is inevitable. Specifications to control this type of cracking are needed.
The proposed research is part of the following strategies of the AASHTO Technical Committee T-10
Concrete Design:
Strategy 1: Keep AASHTO LRFD Concrete Design Specifications current with state-of-the-art
practices.
Strategy 2: Develop or modify articles in Chapter 5 that will facilitate innovative construction
methods for concrete structures.
Strategy 3: Identify and facilitate the advancement of state-of-the-practice through research.
IV. Literature Search Summary
NCHRP Synthesis Topic 47-01 titled “Control of Concrete Cracking in Bridges” includes many refer-
ences related to this topic and has identified the need for this research.

103
V. Research Objective
The objectives of this research are as follows:
• Develop design specifications for the control of flexural cracking in concrete by distribution
of reinforcement, including high-strength steel bars, coated and non-coated bars, and non-
metallic reinforcement.
• Develop design specifications for control of shrinkage and thermal cracking in concrete bridge
decks by distribution of reinforcement, including high-strength steel bars, coated and non-
coated bars, and non-metallic reinforcement.
In particular, the research will be focused on the following primary tasks:
Task 1. Literature review summarizing the latest testing, research outcomes, and studies of
control of concrete cracking by distribution of reinforcement, including high-strength
steel bars, coated and non-coated bars, and non-metallic reinforcement by updating
the report from NCHRP Synthesis Topic 47-01.
Task 2. Investigate the current design methodologies used in the United States and elsewhere
for control of concrete cracking by distribution of reinforcement for different structural
components and exposure conditions.
Task 3. Conduct laboratory testing of concrete specimens of different thicknesses and differ-
ent concretes reinforced with high-strength steel bars, coated and non-coated bars, and
non-metallic reinforcement, with different bar sizes and spacing.
Task 4. Determine acceptable crack widths for durability, aesthetics, and economy.
Task 5. Develop an analytical model corresponding to the results of the specimen testing
program.
Task 6. Recommend necessary revisions to the AASHTO LRFD Bridge Design Specifica-
tions for control of cracking by distribution of reinforcement, including high-strength
steel bars, coated and non-coated bars, and non-metallic reinforcement.
VI. Estimate of Problem Funding and Research Period
Recommended Funding:
Research Project: $490,000

Implementation activities following completion of the research: $10,000
Research Period:
36 months
VII. Urgency and Potential Benefits
The final product from the research will be proposed revisions to the AASHTO LRFD Bridge
Design Specifications for control of cracking in concrete structures by appropriate distribution of
reinforcement. It will expand the existing articles to address design with high-strength steel bars,
coated and non-coated bars, and non-metallic reinforcement. The outcome will be more logical
and practical design procedures for control of concrete cracking using all types of reinforcement.
Without this research, bridge designers will continue to use the existing provisions, which were not
developed for all the types of reinforcement available today.
VIII. Implementation Planning
The final report will include the proposed revisions as a working agenda item for consideration
by the AASHTO Technical Committee T-10 Concrete Design. After review, modification, and
approval by Committee T-10, the proposed revisions will be submitted to the AASHTO Subcom-
mittee on Bridges and Structures as an agenda item for ballot. If approved, the revisions will be
incorporated into the next edition of the AASHTO LRFD Bridge Design Specifications.

104
There are no known institutional or political barriers to the implementation of the anticipated
research results.
IX. Person(s) Developing the Problem Statement
Henry G. Russell, PhD, S.E.

Henry G. Russell, Inc.
720 Coronet Road
Glenview. IL 60025
Phone: (847) 998-9137
Email: henry@hgrconcrete.com
Bijan Khaleghi PhD, P.E., S.E.

State Bridge Design Engineer
Bridge and Structures Office
Washington State DOT, P.O. Box 47340
Olympia, WA 98504-7340
Phone: (360) 705-7181
Email: khalegb@wsdot.wa.gov
X. AASHTO Monitor
Bijan Khaleghi PhD, P.E., S.E.

State Bridge Design Engineer
Bridge and Structures Office
Washington State DOT, P.O. Box 47340
Phone: (360) 705-7181
Email: khalegb@wsdot.wa.gov
XI. Submitted By
Month, day, 2016, submitted by:

Tom Baker, P.E. (Primary Member)
State Bridge and Structures Engineer
Washington State Department of Transportation
P.O. Box 47340
Phone: (360) 705-7207
E-mail: BakerT@wsdot.wa.gov
Please submit completed problem statement at:
http://bit.ly/NCHRP2018Submittal
Questions on the process can be directed to chedges@nas.edu.

Abbreviations and acronyms used without definitions in TRB publications:

A4A Airlines for America
AAAE American Association of Airport Executives
AASHO American Association of State Highway Officials
AASHTO American Association of State Highway and Transportation Officials
ACI–NA Airports Council International–North America
ACRP Airport Cooperative Research Program
ADA Americans with Disabilities Act
APTA American Public Transportation Association
ASCE American Society of Civil Engineers
ASME American Society of Mechanical Engineers
ASTM American Society for Testing and Materials
ATA American Trucking Associations
CTAA Community Transportation Association of America
CTBSSP Commercial Truck and Bus Safety Synthesis Program
DHS Department of Homeland Security
DOE Department of Energy
EPA Environmental Protection Agency
FAA Federal Aviation Administration
FAST Fixing America’s Surface Transportation Act (2015)
FHWA Federal Highway Administration
FMCSA Federal Motor Carrier Safety Administration
FRA Federal Railroad Administration
FTA Federal Transit Administration
HMCRP Hazardous Materials Cooperative Research Program
IEEE Institute of Electrical and Electronics Engineers
ISTEA Intermodal Surface Transportation Efficiency Act of 1991
ITE Institute of Transportation Engineers
MAP-21 Moving Ahead for Progress in the 21st Century Act (2012)
NASA National Aeronautics and Space Administration
NASAO National Association of State Aviation Officials
NCFRP National Cooperative Freight Research Program
NCHRP National Cooperative Highway Research Program
NHTSA National Highway Traffic Safety Administration
NTSB National Transportation Safety Board
PHMSA Pipeline and Hazardous Materials Safety Administration
RITA Research and Innovative Technology Administration
SAE Society of Automotive Engineers
SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act:
A Legacy for Users (2005)
TCRP Transit Cooperative Research Program
TDC Transit Development Corporation
TEA-21 Transportation Equity Act for the 21st Century (1998)
TRB Transportation Research Board
TSA Transportation Security Administration
U.S.DOT United States Department of Transportation

TRANSPORTATION RESEARCH BOARD
NON-PROFIT ORG.
500 Fifth Street, NW U.S. POSTAGE
Washington, DC 20001
PAID
COLUMBIA, MD
PERMIT NO. 88
ADDRESS SERVICE REQUESTED

90000
ISBN 978-0-309-38981-5
9 780309 389815

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

NCHRP SYNTHESIS 500

A Synthesis of Highway Practice

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TOPIC PANEL 47-01

SYNTHESIS STUDIES STAFF

COOPERATIVE RESEARCH PROGRAMS STAFF

NCHRP COMMITTEE FOR PROJECT 20-05

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Copyright National Academy of Sciences. All rights reserved.

Neil Pedersen, Executive Director

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5 CHAPTER TWO TYPES AND CAUSES OF CONCRETE CRACKING

31 CHAPTER THREE EFFECTS OF CONCRETE CONSTITUENT MATERIALS

40 CHAPTER FOUR EFFECTS OF CONSTRUCTION PRACTICES ON CRACKING

44 CHAPTER FIVE EFFECTS OF REINFORCEMENT TYPE ON CRACK CONTROL

Copyright National Academy of Sciences. All rights reserved.

54 CHAPTER SIX INFLUENCE OF CRACKING ON LONG-TERM

61 CHAPTER SEVEN CASE EXAMPLES

68 CHAPTER EIGHT Conclusions and Suggestions for Future Research

83 APPENDIX A Survey Questionnaire

88 APPENDIX B Summary of Responses to Survey Questionnaire

101 APPENDIX C Cross Reference Table for AASHTO

102 APPENDIX D Research Problem Statement

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Control Of Concrete Cracking in Bridges

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Copyright National Academy of Sciences. All rights reserved.

Objectives and Scope

The objectives of this synthesis are to

• Concrete mix design and performance requirements,

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The text of the synthesis is organized as follows:

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Types and Causes of Concrete Cracking

• Cracks caused by externally applied loads, and

Plastic Shrinkage Cracks

Plastic Settlement Cracks

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Drying Shrinkage Cracks

Cracking In Bridge Decks

Copyright National Academy of Sciences. All rights reserved.

5 CHAPTER TWO TYPES AND CAUSES OF CONCRETE CRACKING

31 CHAPTER THREE EFFECTS OF CONCRETE CONSTITUENT MATERIALS

44 CHAPTER FIVE EFFECTS OF REINFORCEMENT TYPE ON CRACK CONTROL

54 CHAPTER SIX INFLUENCE OF CRACKING ON LONG-TERM

68 CHAPTER EIGHT Conclusions and Suggestions for Future Research

101 APPENDIX C Cross Reference Table for AASHTO