Flexible Pavement Rehabilitation Manual: California Department of Transportation

STATE OF CALIFORNIA
California
Department
of
Transportation
FLEXIBLE
PAVEMENT
REHABILITATION
MANUAL
Revised: June 1, 2001

Flexible Pavement Rehabilitation Manual June 2001
______________________________________________________________________________________
DISCLAIMER
This manual is intended for the use of Caltrans personnel. Engineers and agencies
outside of Caltrans may use this manual at their own discretion. Caltrans is not
responsible for any work performed by non-Caltrans personnel using this manual.
ACKNOWLEDGMENT
The information contained in this manual is a result of efforts of many individuals

in the Structural Section Design and Rehabilitation Branch (SSD&R). Gary Mann,
P.E. and Paul Mason, P.E., with a combined experience of 40 years of pavement
structural section design and rehabilitation, are the principal authors of this
publication. The contributions of engineers and technicians who have worked and
are presently working in SSD&R are also acknowledged.
ii
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TABLE OF CONTENTS
Chapter - Section
1 GENERAL
1 – 10 Background
1 – 20 Foreword
2 PERFORMING A DEFLECTION STUDY

2 – 10 Equipment
2 – 20 Establishing Test Sections
2 – 30 Pavement Background Information
2 – 40 Collecting Field Data
2 – 50 Measuring Deflections
2 – 60 Converting to Equivalent Deflectometer Values
2 – 70 Mean and 80th Percentile Deflections
2 – 80 Preparing a Deflection Map
3 INTRODUCTION TO AC PAVEMENT REHABILITATION DESIGN

3 – 10 Design Governed by Structural Adequacy
3 – 20 Design Governed by Reflective Cracking
3 – 30 Design Governed by Ride Quality
3 – 40 Choosing the Design Recommendation
4 FLEXIBLE PAVEMENT REHABILITATION DESIGN GUIDE

4 – 10 Basic Overlay Using DGAC
4 – 20 Rubberized Asphalt Concrete (Type G)
4 – 30 Stress Absorbing Membrane Interlayers
4 – 40 Cold Recycled Asphalt Concrete Pavement
4 – 50 Hot Recycled Asphalt Concrete Pavement
4 – 60 Remove and Replace
4 – 70 Asphalt Concrete Overlay Placed on a Cushion Course
4 – 80 Cushion Course Design With Drainage Layer
4 – 90 Asphalt Concrete Overlay With Drainage Layer
5 APPENDIX
5 – 10 Guidelines for Involving Moisture and Temperature in Flexible Pavement Rehabilitation
5 – 20 Identifying and Recording Distress
5 – 30 Abbreviations
5 – 40 Definitions
5 – 50 Bibliography
6 TABLES
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CHAPTER 1 deflections eventually provided the basis

for the application of pavement
deflection data to overlay design.
GENERAL However, since tolerable deflection
values were collected for roads with
Traffic Indices (TI’s) of approximately
This manual delineates the basic design 9, results of laboratory fatigue tests on
strategies of the 1979 “Asphalt Concrete asphalt concrete samples were used to
Overlay Design Manual” plus the many establish a method to adjust tolerable
changes in procedures, and incorporates deflection levels for other TI values (2).
the use of new strategies and materials
presently being used by Caltrans. It is In 1960, California began using
intended as a tool to provide guidance to deflection data in conjunction with the
those who are recommending asphalt tolerable deflection as the basis for
concrete pavement rehabilitation for overlay design. Data accumulated on
planning, design and maintenance of the the deflection values for various
state’s highways. Caution and thicknesses of AC pavement with
engineering judgment must be exercised cement treated base, or aggregate base,
throughout the investigation and design subjected to various traffic loadings
process. along with the tolerable deflection
criteria already established, provided the
basis of the Caltrans overlay design
1 – 10 Background procedure. By 1966, approximately 80
overlay projects; including state
Since 1938, deflection measurements highways, county roads, and city streets;
have been utilized for the evaluation of had been designed by deflection
flexible pavement. In 1951, the analysis.
Laboratory at the Division of Highways
initiated a series of comprehensive After almost 20 years of research into
deflection research studies in an effort to determining asphalt concrete pavement
establish relationships between deflections and relating these deflections
pavement deflections and pavement to pavement performance,(3) the data
performance. The results and collection and design procedures were
conclusions of the first formal study formally adopted in 1969. California
were published in 1955 (1). An Test Method 356 “Methods of Test to
evaluation of the data, with respect to Determine Flexible Pavement
pavement deflections versus pavement Rehabilitation Requirements By
conditions, permitted the establishment Pavement Deflection Measurements,”(4)
of the concept of "tolerable deflection" defined pavement rehabilitation
criteria for a variety of asphalt concrete requirements on state highways in
(AC) structural sections*. Tolerable California. During this time the primary
overlay material was dense graded
asphalt concrete.
*
The term "tolerable deflection," refers to the
level beyond which repeated deflections of that In 1974, changes based on the
magnitude would produce fatigue cracking in the performance of newly constructed
surface prior to the planned design period of the
pavement.
highway projects under study since 1964
1-1
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simplified the procedure for determining of the roadway wheel path areas. (One
an AC overlay thickness (3). Revised wheel path with continuous alligator
deflection attenuation data and tolerable cracking was considered to be 50 percent
deflection levels of AC pavements were and continuous cracking in both wheel
also included. paths would be 100%.)
In 1979, the “Asphalt Concrete Overlay 1 – 20 Foreword

Design Manual”(5) was published. This
manual provided the methods: (1) to be Headquarters Maintenance along with
used for acquiring information regarding each district office determines which
the existing asphalt concrete pavement, portions of the California highway
(2) to design AC pavement overlays system are candidates for rehabilitation.
using deflections for structural adequacy The Pavement Management System
based on California Test 356, (3) to (PMS) is the primary tool used in
retard reflective cracking and (4) to determining where repairs are needed
restore ride quality. and how available funds will be
apportioned statewide.
Environmental concerns and the State’s
commitment to recycle as much roadway Besides rehabilitation for structural
material as economics permit have also adequacy, when an existing roadway is
influenced rehabilitation methods. being widened the existing pavement
Consequently, over the past 21 years, should be brought up to the same life
Caltrans* rehabilitation strategies have expectancy as the new pavement.
increased in number with new materials,
interlayers, recycling of existing The Pavement Condition Inventory, a
pavements, and the addition of waste report generated under the PMS, will
products (such as rubber) in asphalt “trigger” a section of roadway when the
concrete. ride quality is poor. The design for
alleviating a poor ride problem should
A study was published in 1980 (6) that also provide an increased service life for
reviewed the actual service life of the pavement (normally 10 years).
pavement overlays designed by
California Test Method 356. The design When the new lanes are added, the
period of the overlays in this study was existing shoulder may be called upon to
10 years. The average service life was carry a wheel path. A deflection study
found to be 11.6 years. Judgment as to will determine if it will support the new
length of service was recognized to be loads or if any up-grade is necessary.
entirely subjective and, thus, susceptible
to variation. However, the term “service When construction requires that public
life" was defined in this report as the traffic be detoured to an existing street
period of time until the extent of load- or roadway for a period of time, a
associated alligator cracking or patching before-and-after study may be necessary
reached a combined total of 30 percent to determine the extent of added distress
and to develop a recommendation to
*
The California Division of Highways became bring the pavement back to its intended
the California Department of Transportation service life.
(Caltrans) on July 1, 1973.
1-2
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Each design requires an evaluation based return the roadway to an acceptable level
on three components: providing of service.
structural adequacy, retarding reflective
cracking from the underlying layer and There are many variations in materials,
improving the ride quality. traffic loads and environment that affect
the performance of pavement structural
The project engineer should consult the sections. This makes it impossible to
regional or district materials engineer or develop hard and fast rules for the
the district pavement engineer early in rehabilitation of pavements. Therefore,
the project development process in order the project engineer should rely on the
to reduce the lag time between experience, judgment and guidance of
conception and construction of the engineers in pertinent functional
project. Pavement deflection studies and engineering areas who are familiar with
rehabilitation recommendations should design, construction, materials, and
be requested early in the process to maintenance of pavements in the
provide accurate information for geographical area of the project.
estimating project costs.
The use of the metric system is
Development of a recommendation to encouraged and prevalent in State
rehabilitate an existing AC pavement contracts. However, the English system
requires collecting background data as lends itself better to the use of this
well as collecting field data. Thorough manual since deflections in all previous
investigation of the pavement surface, research and current field studies are
deflection measurements of the existing measured in thousands of an inch
pavement and knowledge of the (0.001-inch) for the California
subsurface conditions are all necessary. Deflectometer as well as other devices.
Finally, all the assembled information All calculations in this manual are in the
previously acquired, along with the English system and final results are in
calculations, are used to determine the metric equivalent.
amount of rehabilitation necessary to
1-3
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CHAPTER 2 done at least annually. For routine

deflection measurements since 1969
Caltrans has been using the Dynaflect.
PERFORMING A
For engineers and agencies outside
DEFLECTION STUDY
Caltrans using this design method,
consideration should be given to
2 – 10 Equipment correlating testing equipment with a
truck having the axle weight, tire
Since the early 1960’s, Caltrans research spacing, and tire pressure that conforms
data have been based on deflections to the specifications of the California
obtained by the "California Traveling Deflectometer. (See California Test
Deflectometer” (2) (Photo 1). The trailer 356).
consisted of a mechanical arm that
placed the probe between the dual
wheels on a single rear axle. The dual
wheels were reconfigured so that the
probe was easy to insert. The probe
measured the vertical movement
(deflection) of the pavement as the dual
wheels passed the site.
The Traveling California Deflectometer

built by Caltrans, was one of a kind and
operated for routine work until 1969 and
for research until about 1980. After it
was no longer practical to use the
California Traveling Deflectometer due
to the age of its electronics, the trailer
portion was retained,) and used to apply
loads to pavement measurement sites to
perpetuate the standard deflection
device. This is now referred to as the
"California Deflectometer". A
Benkelman Beam* (Photo 2) is used to
measure the deflection at the site. Either
the California Traveling Deflectometer
or the California Deflectometer were
used in the development of Caltrans’
flexible pavement overlay design
method and all past research projects.
The California Deflectometer is

currently used to correlate other
deflection devices such as the falling
weight deflectometer (Photos 3 and 4)
and Dynaflect (Photo 5). Correlation is
2-1
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Photo courtesy of Roger Smith
Photo 1 – California Traveling Deflectometer
Photo 2 - Benkelman Beam
2-2
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Photo 3 - KUAB Falling Weight Deflectometer
Photo 4 – JILS Falling Weight Deflectometer
2-3
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Photo 5 – Dynaflect
2-4
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2 – 20 Establishing Test Sections measured in the OWP, wherever

possible. Side clearance to fixed objects
Test sections are representative portions (i.e. guard railing) may make this
of a roadway being considered for unattainable.
rehabilitation. They are selected as
being representative of the entire mile, If the multi-lane project is greater than a
which helps to keep the amount of mile in length, a 0.20-mile test section
preliminary survey work to a reasonable should be selected for each mile for both
level on projects that are several miles outer lanes. For each five miles of
long. roadway, one 0.20-mile test section
should be selected for each of the inner
Traffic safety should always be lanes. Additional test sections will be
considered when selecting test sections. required if structural section changes
Areas of inadequate sight distance occur and/or roadway appearances are
should be avoided. The district not uniform.
coordinator or area maintenance
superintendent should be contacted for Pavement deflections should be
assistance and for traffic control. measured from the beginning to the end
on ramps or connectors using the whole
For two-lane highways, if the project is as a test section. Short ramps require a
less than a mile in length, the entire short testing interval in order to obtain
project is considered the test section. sufficient readings. Extremely long
Pavement deflections are measured at ramps testing may be longer than the
approximately 0.01-mile (0.02-km) normal 0.2-mile test section. If the ramp
intervals in the outside wheel path is closed to traffic when testing, the
(OWP) in both lanes. When projects are wheel path with the most distress should
greater than a mile in length, a 0.20-mile be used. Otherwise the wheel path that
(0.32-km) test section (21 deflection allows the traffic to pass safely is tested.
readings at 0.01-mile intervals) is
selected to represent each lane mile. If Shoulders that will carry future traffic
possible, test sections are staggered from should have test sections established
lane to lane to obtain a representative according to the normal procedure in this
coverage of the roadway. section.
For multi-lane highways if the project is Sometimes state highways are also city
less than a mile in length the entire streets. Test section determinations on
project is considered the test section. city streets are performed in the same
Pavement deflections are measured at manner as described for two-lane
approximately 0.01-mile intervals in the roadways and multilane facilities. It is
outside wheel path in both outside lanes. often necessary to select a greater
If possible, at least one 0.20-mile test number of test sections on city streets or
section* is selected for each of the inner test continuously due to frequent
lanes, with pavement deflections changes in structural section and/or
roadway condition.
*
Normally, 0.20-mile test sections consist of 21
deflection readings at 0.01-mile intervals. The Engineering judgment should always be
measurements are usually made in the outside wheel
path or the location with the most distress.
used in selecting the number of test sites
2-5
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for pavement deflection measurements. date of placement, and the project’s

The suggested test frequencies described design Traffic Index (TI).
above are the minimum number
recommended. Structural section SSD&R has records on previous
changes are not always clearly visible in deflection studies. If the District’s
the field, but can usually be located from records show no maintenance or
large changes in deflection rehabilitation was done for the project in
measurements and confirmed by core question, the previous structural section
data. Therefore, whenever there appears data may be used. If information is
to be a need for additional information, limited or not available, pavement cores
make as many deflection measurements must be removed to provide this
as necessary. information.
As the need for additional lanes has Previous deflection studies for the
occurred, widening of the roadway has project found in the SSD&R files, where
sometimes created two different no maintenance or rehabilitation has
structural sections even within a single been done, can be used to determine a
lane. These can usually be noticed by a rate-of-change in deflections that may be
longitudinal crack at the joint. A test considered when designing new
section on each of the structural sections rehabilitation strategies. Normally,
should be selected for use in the deflections increase with age beginning
rehabilitation study. several months after construction if the
pavement is under traffic loads.
Occasionally, a return to a project may
be required for additional testing after A previous study may have been done
reviewing the initial deflection data in when moisture was in the structural
the office. section. Consequently, those deflections
may be higher than in the current study.
If this happens, the previous, higher
deflections should be used to design the
2 – 30 Pavement Background current rehabilitation.
Information
Background information is obtained

from both the Region/District and the 2 – 40 Collecting Field Data
files of the Structural Section Design and
Rehabilitation (SSD&R) Branch, Office A pavement condition inspection is as
of Materials Engineering and Testing important to the design engineer as the
Services. deflection values. The function of the
pavement condition inspection is to
When requesting a pavement deflection obtain the necessary information to be
study from SSD&R, the District used in conjunction with the evaluated
Materials Engineer (DME) should deflection values to determine the
provide at least the following appropriate rehabilitation strategies.
information: the original structural
section data, maintenance overlays and The pavement condition inspection
provides data that may convince the
2-6
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designer to adjust the rehabilitation to 2 – 60 Converting to Equivalent

meet the special requirements of that Deflectometer Values
section of pavement.
Caltrans, at the present time, uses the
The inspection of the project should Dynaflect as its primary deflection-
describe the general condition of the measuring device. Although repeatable
pavement in terms of visual appearance instruments, each Dynaflect has a unique
including the type, severity and extent of correlation curve. The correlation curve
distress. This should include items such for each Dynaflect vs. California
as rutting, bleeding, raveling, patching, Deflectometer has been determined,
potholes, shoving (sometimes called through experience and testing, to be
slippage), corrugations, pumping, non-linear and unique. SSD&R has a
delamination, and the various types of conversion chart for each of its
cracking. Dynaflects to be used to convert each
individual deflection measurement to the
Also, an inspection of the project should equivalent California Deflectometer.
include other details that should be
recorded such as the existing structural When using the falling weight
section changes; permanent vertical deflectometer, convert the mean and 80th
control features that will limit an percentile deflection values to equivalent
increase in profile grade; any localized California Deflectometer values using
drainage problems; embankment appropriate correlation curves.
settlement; and areas of deep cuts and
fills within the test section. A comparison of each deflection-
Representative test sections and other measuring device to the California
important features recorded, such as Deflectometer should be performed at
failed areas whether tested or not tested least once a year. The correlation curve
should be photographed and recorded. results can be calculated and placed in a
Air and pavement temperatures should conversion chart for ease of use.
be measured. Date and time of
measurement should be recorded.
2 - 70 Mean and 80th Percentile
Deflections
2 – 50 Measuring Deflections Individual deflection readings for each

test section should be reviewed prior to
California Test 356 should be consulted determining mean and 80th percentile
when pavement deflection values. This review may locate possible
measurements will be obtained with areas that are not representative of the
different testing devices (4). A copy of entire test section.
the test method can be downloaded from
the following Caltrans’ Internet address: An example would be a localized failure
(Address as of June 2001) with a very high deflection. It may be
more cost effective to repair the various
www.dot.ca.gov/hq/esc/ctms/index.html failed sections prior to rehabilitation
Thus, the high deflection values in the
repaired areas would not be included
2-7
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when calculating mean and 80th D80 = x + 0.84 s

percentile values for the representative
test sections. Where:
When similar deflection values are
x = mean deflection for a test section
found within a test section they should
be analyzed as a group. There may be
D80 = 80th percentile of the
several groups within the test section or
deflections at the surface for a
only one. If all deflections are similar,
test section, in inches
the entire test section is analyzed as a
whole. With this in mind, engineering
s = standard deviation of all test
judgment must always be utilized in
points for a test section
analyzing deflection data.
The mean deflection level for a test

s=
(
∑ Di − x )
2
section is determined by dividing the

n −1
number of individual deflection
measurements into the sum of the
deflections.
x =
∑D i
Where:
x = mean deflection for a test section
Di = an individual deflection
measurement in the test section
n = number of measurements in the

test section
The 80th percentile deflection value

represents a deflection level at which
approximately 80 percent of all
deflections are less than the calculated
value and 20 percent are greater than the
value. Thus the design will provide
thicker rehabilitation than using the
mean value. The 80th percentile
deflection values are obtained using the
following equation:
2-8
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Example 2-1: Determine the mean and D80 = x + 0.84 s

the 80th percentile from the evaluated
= 0.0345 inch + 0.84(0.0033 inch)
deflection values (assume no isolated
D80 = 0.037 inch (0.940 mm).
failures). The Dynaflect data obtained
from a 0.20-mile (0.32-km) test section 2 - 80 Preparing a Deflection Map
is converted to the equivalent California
Deflectometer deflection as follows: A deflection map is a sketch of the
project illustrating D80 deflection levels
Test Dynaflect California for each test section. The purpose of the
Readings Deflectometer
deflection map is to show a visual
(in. x 10 -3) Deflection
representation in order to determine if
(inch)
certain areas of the project should be
1 1.68 0.035
grouped and analyzed separately (by
2 1.43 0.031 observing the differences in deflection
3 1.21 0.027 levels). Deflection values should not
4 1.92 0.039 only be looked at along the lane, but
5 2.08 0.041 from lane to lane and travel direction.
6 1.66 0.035
Traffic can vary considerably from lane
to lane and in opposing directions, thus
7 1.73 0.036
causing different distress and deflection
8 1.59 0.034 levels. Rehabilitation requirements and
9 1.83 0.037 limits can then be determined for each
10 1.74 0.036 direction or lane.
11 1.50 0.032
See Figure 1 for an example of a
12 1.40 0.030
"deflection map."
13 1.39 0.030
14 1.58 0.033
15 1.63 0.034
16 1.79 0.037
17 1.90 0.038
18 1.66 0.035
19 1.74 0.036
20 1.54 0.033
21 1.73 0.036
Solution 2-1:
Sum of 21 deflections = 0.725 inch

s = 0.0033 inch
x =
∑D i
n
= 0.725/21 = 0.0345 inch
2-9
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Figure 1
EXAMPLE OF DEFLECTION MAP

(Not to Scale)
Project Limits
Photo 6
Photo 5
Photo 4
Photo 7
Photo 3
Photo 2
Photo 1
24 30 30 13 14 15 14
SB
80th percentile deflections (10-3 inches) for
0.02-mile test sections.
NB Pavement deflections taken at 0.01-mile intervals.
28 28 34 20 18 13
Photo 8
Photo 9
Photo 13
Photo 12
Photo 10
Photo 11
PM 62.0
PM 63.0
PM 64.0
PM 65.0
PM 66.0
PM 59.0
PM 61.0
PM 60.0
Avg. 80th percentile Avg. 80th percentile

deflection level deflection level
= 0.029 in. = 0.015 in.
Note: All deflections are in terms of equivalent California Deflectometer values.
Date Tested: 4/21/00

Traffic Index (10 year) = 9.0
2-10
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CHAPTER 3 select the corresponding TI for the new

ESAL.
There are three components to be

INTRODUCTION TO considered when designing flexible
AC PAVEMENT pavement rehabilitation:
REHABILITATION DESIGN
1) Structural adequacy upgrade;
Currently, Caltrans uses the philosophy 2) Reflective crack retardation; and
of extending service life of a pavement 3) Ride quality improvement.
for a 10-year period of time for
rehabilitation. However, the design 3 - 10 Designing for Structural
engineer may request pavement Adequacy
rehabilitation for a different design
period. The design procedure is the Deflections are used for determining the
same for a different design period. It is thickness requirements for rehabilitation
accomplished by using the appropriate of asphalt concrete (AC) pavements
Traffic Index (TI) for the period of time when considering structural section
for the design. adequacy. Condition and structural
section of the existing roadbed together
When determining the rehabilitation with measured deflections and the
alternatives, the engineer must know projected TI provide the majority of the
both the design period requested and the information to be used during
TI for the pavement being evaluated. consideration for structural adequacy.
Traffic Index is a measure of the number
of equivalent 18,000-lb (80-kN) single Once the data has been collected and the
axle loads (ESAL’s) expected in the deflections of the test sections have been
design lane over the design period. The reduced to 80th percentile deflections
TI does not vary directly with ESAL’s (D80’s) and placed on a project
but rather exponentially according to the deflection map, the design process
following formula as illustrated in Table involves both calculations and
603.4A of the “Highway Design engineering judgment.
Manual.” (8)
The project deflection map should be
6 0.119
TI = 9.0 (ESAL / 10 ) examined for similar D80 values.
Adjacent test sections with similar D80
Where: TI = Traffic Index values should be grouped together.
ESAL = Equivalent 18,000-lb There may be several groups within the
Single Axle Loads project or only one. If all D80 values are
similar, the entire project may be
analyzed as a whole.
If that TI is unknown and the 10-year TI A group is a collection of adjacent test
is known, use Table 603.4A in the HDM sections that have similar values for the:
to establish the ESAL’s. Then
proportion from the ten-year ESAL to • Average 80th percentile deflection
the ESAL of the new design life. Finally (D80).
3-1
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• Average existing asphalt concrete average existing AC pavement thickness

pavement thickness. and type of base to determine the
tolerable deflection at the surface (TDS)
• Type of base. for the group using Table 1 (Chapter 6).
• Traffic Index (TI). For existing AC pavement over

untreated base material such as
Each of these has an influence on the aggregate base (AB), native material,
rehabilitation. etc., use the TDS corresponding to the
thickness of the existing AC pavement
Test sections should not be grouped and the appropriate TI.
together if the existing AC thickness
varies more than 0.10 ft (30 mm), the For existing AC pavement over treated
type of base materials is different, or the base or portland cement concrete (PCC),
TI is different. These influence the use the TDS values in the row for CTB
tolerable deflection level that is used in and the column for appropriate TI.
determining the rehabilitation. Similar However, if the underlying CTB
groups of test sections can be analyzed thickness is less that 0.35 ft (105 mm),
together. consider it an untreated base and
determine the TDS from the upper part
D80 values should not be examined only of the table corresponding to the
along the lane, but should be examined thickness of the existing AC pavement
from lane to lane and in the direction of and the appropriate TI.
travel. Traffic may vary considerably
from lane to lane and in opposing In locations where existing AC
directions, thus causing different distress pavement is over a treated base and the
and deflection levels. Rehabilitation measured deflections are high, the
requirements and limitations should be treated base may not be performing as it
considered for each direction or lane as should. The treated base layer is no
is appropriate from the data and to meet longer carrying the load as it was
the needs of the project site. originally designed to do. It may have
deteriorated to the point where this layer
Suggestion: is acting more like an untreated base. In
this case, the rehabilitation should be
In selecting groups of similar D80 values, designed as though the existing
it is suggested that only adjacent test structural section is AC over untreated
sections with D80 values that differ less base.
than about 0.010 inch (0.254 mm)
should be grouped together. More than Choosing the appropriate existing
0.010-inch difference will most likely structural section interaction – AC over
produce different thickness treated base or AC over untreated base –
requirements. should be made carefully. This choice
will greatly influence the TDS, and the
Once groups with similar D80 values, resulting thickness of rehabilitation
structural sections, types of bases and strategies.
TI’s have been identified; average the
D80 values for each group. Use the TI,
3-2
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Suggestion: Where:
When the D80 value for deflections of a PRD = Percent Reduction in

test section of AC pavement over treated Deflection Required at the
bases is greater than 0.014 inch, the surface, as percent
rehabilitation may be designed as
though the existing structural section is TDS = Tolerable Deflection at the
AC over untreated base. Surface, in inches
Engineering judgment is required when D80 = 80th Percentile of the

trying to determine if the treated base is Deflections at the surface for a
performing satisfactorily. Besides test section in inches
deflections, the condition of the
pavement surface should be considered. In Caltrans, structural section design is
The greater the amount of alligator based on the concept of gravel
cracking, the more likely the treated base equivalence. This same concept is used
layer is not carrying the load as in flexible pavement rehabilitation.
originally designed. But, if the distress
is mainly transverse cracks without
alligator cracking and localized failures,
For rehabilitation, the additional gravel
the treated base is probably still intact
equivalence (GE) required is determined
even though the D80 value is greater than
from the calculated percent reduction in
0.014 inch. D80 values of as high as
deflection and Table 2. It is the amount
0.020 inch have been measured over
of AS gravel that will provide sufficient
intact treated base.
strength to reduce the deflections to the
tolerable level.
A gravel factor (Gf) expresses the

Occasionally on an older pavement, only
relative value of various materials when
minimal distress is apparent from the
compared to gravel. The gravel factor
condition survey and the average D80 is
(Gf) is given to a material that, when
less than the TDS. In this case,
divided into the gravel equivalence
corrective repair may not be necessary
required, will provide the layer thickness
other than a seal coat that will seal
of the material.
cracks, improve appearance, delay
oxidation of the asphalt concrete and Note that for new pavement design the
prolong the pavement life. Gf for asphalt concrete varies with the
If the average D80 is greater than the TI [Table 608.4, of the Highway Design
TDS, determine the required percent Manual]. However, for most types of
reduction in deflection at the surface rehabilitation (overlay design being
(PRD) to restore structural adequacy as one), the Gf has been established at 1.9
follows: for all Traffic Indices.
AverageD80 − TDS
PRD = (100)
AverageD80
3-3
______________________________________________________________________________________
Commonly Used Gf for Rehabilitation is especially applicable when an increase

in the profile grade is limited.
Asphalt Concrete 1.9
Example3-1: Determine AC overlay
Hot Recycled thickness requirements to restore
1.9
Asphalt Concrete structural adequacy. The 10-year Traffic
Index (TI10) is 11.0.
Cold Recycled
1.5 80th Percentile Existing Structural
Asphalt Concrete Location
Deflection Section
AC Below the PM 1.00 to 0.025 inch 0.40 foot AC
1.4
Analytical Depth PM 3.50 0.67 foot AB
1.00 foot AS
Aggregate Base 1.1
Aggregate Solution 3-1:

1.0
Subbase
Given: TI10 = 11.0
Native Soil 0 Average D80 = 0.025 inch
AC thickness = 0.40 ft
Step 1:
When the volume of traffic increases to Obtain tolerable deflection at the
the level that new lanes should be added, surface (TDS).
the existing shoulder may be called upon Use Table 1 (Chapter 6):
to carry a wheel path. If the shoulder AC = 0.40 ft and TI = 11.0
pavement has not carried traffic loads TDS = 0.012 inch
and fatigue cracking is absent,
engineering judgment is required to Step 2:
analyze the measured deflections on the Compare average D80 to TDS.
shoulder. 0.025 > 0.012
Rehabilitation for structural
Oxidized asphalt pavement may be adequacy is indicated.
“bridging” rather than producing a
deflection basin. The deflections would Stem 3:
be lower than for a normal deflection Calculate Percent Reduction in
basin. To assist in making a Deflection (PRD) required.
determination on whether the pavement
is bridging, removed cores may be  0.025 − 0.012 
brought to the lab for testing the in-place  (100) = 52%
 0.025 
asphalt properties. This should be
emphasized especially when the lighter
Step 4:
deflection equipment is used.
Determine Gravel Equivalence
If the design TI is high, a new structural (GE) required for deflection
section designed using the R-value of the reduction.
underlying material may be appropriate Use Table 2; Column A)
for the shoulder turned into a lane. This GE = 0.68 ft
3-4
______________________________________________________________________________________
Step 5: minimum thickness of 0.45 ft. (135 mm)

Determine the required thickness may be appropriate.
of AC overlay.
For a design life different from a 10-year
GE 0.68 design, a slight modification changes the
Overlay = = = 0.36 ft thickness. For a five-year design,
Gf 1 .9
experience has determined the thickness
should be approximately 75 percent of
Round to 0.35 ft (105 mm).
the ten-year design thickness. For a
twenty-year design, use 125 percent.
Recommendation: 0.35-ft (105-mm)
overlay of DGAC. As always, exceptions will occur and
engineering judgment will be necessary
for final design. Factors to be
3 - 20 Design Governed by Reflective considered that might influence the
Cracking engineer to increase the thickness are:
Reflective crack retardation of the new (1) Type, sizes, and amounts of surface
overlay needs to be considered. cracks.
Retarding the propagation of cracks
from the existing pavement into the new (2) Extent of localized failures.
AC overlay will extend its service life.
(3) Existing structural section material
For AC pavements over untreated bases, and age.
the thickness of a new DGAC overlay
(4) Thickness and performance of
should be at least half the thickness of
previous rehabilitation.
the existing asphalt concrete up to a
maximum of 0.35 ft (105 mm). Or, if (5) Environmental factors.
the existing AC pavement is to be
milled, the thickness of the new AC (6) Anticipated future traffic loads
should be half the thickness of the (Traffic Index).
remaining pavement up to a maximum
of 0.35 ft.
Unfortunately, there are no set criteria
For AC pavements over a treated base or that will aid the engineer in the decision
PCC the general guideline (exceptions process in regards to designing to
will occur) for a ten-year design is a prevent reflective cracking. Experience
minimum overlay of 0.35 ft (105 mm) of with similar roadways repaired in the
new dense graded asphalt concrete general area; past overlays and their
(DGAC). This was developed by performance; and discussions with local
experience and is usually adequate for maintenance and construction personnel
retarding reflective cracks. An are all part of the data gathered to be
exception might be when the underlying considered in the final decision and
material is a thick PCC such as on an engineering judgment process.
overlaid PCC freeway that was not
cracked and seated. In this case a
3-5
______________________________________________________________________________________
3 - 30 Design Governed by Ride 3 - 40 Choosing the Design

Quality Recommendation
The Pavement Management System The final choice of the recommended

records ride quality as part of their rehabilitation alternative is based on
pavement condition inventory. The choosing a strategy that will provide a
International Roughness Index (IRI) for total structural section thickness that is
each lane is measured for the Pavement adequate to resist the anticipated loading
Condition Survey. (IRI has replaced the it will experience throughout its design
Ride Score. The Ride Score of 45 or period, the potential for reflective
more will “trigger” a project. The cracking and to improve ride.
equivalent IRI is not yet determined.)
When ride quality measurements Once the rehabilitation strategies have
indicate that the pavement needs been determined to correct for lack of
improvement, procedures are needed to structural adequacy, to retard reflective
smooth the pavement. At least two cracking and to improve ride quality, a
options emerge as viable solutions: single strategy must be chosen which
will be sufficient for all three conditions.
(1) Place an asphalt concrete overlay In addition to choosing a rehabilitation
thick enough to be placed in two lifts strategy to correct the three criteria listed
[0.25-ft (75-mm) minimum]. earlier, constructability concerns must be
addressed.
(2) Cold plane the existing pavement
prior to placing the new asphalt Prior to placement of asphalt concrete on
concrete. an existing pavement, some preparation
is required besides what is specified in
Ride quality will ultimately govern the Standard Specifications 39-4.01. Cracks
rehabilitation strategy design if the wider than 0.25 inch (5 mm) should be
requirements for structural adequacy and sealed; loose and/or spalling pavement
reflective crack retardation are less than removed; and potholes and localized
0.25 ft (75 mm). failures repaired. Routing cracks before
applying crack sealant has been found to
Please note that if the two-lift option is
be beneficial. The width of the routing
chosen, the July 1999 Standard
should be 0.25 inch (5 mm) wider than
Specification Section 39–6.01(9) gives
the crack width. The depth should be
the contractor the option to place 0.25 ft
equal to the width of the routing plus
(75 mm) in one layer. Any rehabilitation
0.25 inch (5 mm). In order to alleviate
report that recommends this overlay
the potential bump in the overlay from
thickness for improving the ride quality,
the crack sealant, leave the crack sealant
should point out in the report that the
0.25 inch (5 mm) below grade to allow
overlay needs to be placed in two layers
for expansion. Design recommendations
and specified as such in the project
should include a reminder of these
special provisions.
preparations.
It has been found that during

construction a dense graded AC layer of
less than 45 mm (0.15 ft) may cool
3-6
______________________________________________________________________________________
considerably before adequate Ride Quality:

compaction occurs. Therefore, for a A 0.25-ft DGAC overlay placed
surface course for rehabilitation, in two layers.
Caltrans generally uses a minimum (Section 3-30).
thickness of 45 mm (0.15 ft). The
minimum thickness for rubberized AC is Discussion 3-2:
30 mm (0.10 ft) since it is placed at a • A second option for ride quality is to
higher temperature. mill the existing rough pavement to
remove much of the surface
Structural Section Design and undulations prior to placing the new
Rehabilitation Branch (SSD&R) designs AC overlay. Milling off 0.10 to 0.20
asphalt concrete thicknesses in 0.05-ft ft (30 to 60 mm) will usually be
increments. With the change to metric sufficient. Milling will change D80
values, SSD&R increases the and require additional design
thicknesses by 15 mm for each 0.05-ft calculations.
increment (Table 5). Please note that
this is not an exact mathematical • Cold planing and replacing the
conversion. existing surface with DGAC or hot
recycled AC to the same grade
Example3-2: Determine the AC would provide a good solution for
rehabilitation requirements. The 10-year reflective cracking and ride quality.
Traffic Index (TI10) is 11.0. There are (This is discussed in Section 4-50 of
no restrictions on an increase in profile this manual.)
grade.
• A 0.35-ft DGAC overlay may
increase the profile grade beyond the
Location 80th Percentile Existing Structural
allowable if there are restraints such
Deflection Section as are found in urban areas.
PM 1.00 to 0.025 inch 0.40 foot AC
PM 3.50 0.67 foot AB
1.00 foot AS Recommendation 3-2: 0.35-ft (105-mm)
overlay of DGAC.
Solution 3-2:
Recommendations to be considered:
Structural Adequacy:
A 0.35-ft DGAC overlay. Refer
to Example 3-1. (Rubber AC
alternatives are discussed in
Section 4-20 of this manual.)
Reflective Cracking:
A 0.20-ft DGAC overlay. (One-
half existing AC thickness.)
3-7
______________________________________________________________________________________
CHAPTER 4
s = standard deviation of all
deflections for a test section
FLEXIBLE PAVEMENT
REHABILITATION DESIGN Di = an individual deflection
GUIDE measurement in the test section
4 – 10 Basic Overlay Using DGAC n = number of measurements in the

test section
See Chapter 3 for a complete discussion
of Basic Overlay design using dense 3. Calculate the 80th percentile
graded asphalt concrete. D80 = x + 0.84 s
Dynaflect deflection values (Caltrans 4. Determine the Tolerable Deflection at

primary deflection device) converted to the Surface (TDS).
equivalent California Deflectometer
values are used for determination of
overlay thickness.
Determine the TDS from the Tolerable
* Deflection Chart (Table 1) with the
1. Calculate Mean
x =
∑D i
design Traffic Index (TI) and either the
thickness of the existing asphalt concrete
n (AC) pavement or the type of base data.
2. Calculate Standard Deviation** If D80 is at or below the TDS, then the
pavement is considered structurally
s=
(
∑ Di − x )
2
adequate and any overlay thickness
n −1 should be based on reflective crack
retardation and/or ride score reduction.
If D80 is greater than the TDS, then the
where:
overlay required for structural adequacy
is determined along with the need for
x = mean deflection for a test reflective crack retardation and/or ride
section score reduction.
D80 = 80th percentile of the 5. Calculate the Percent Reduction in

deflections at the surface for a Deflection at the surface:
test section in inches
D80 − TDS
*
When determining the Mean, omit any
PRD = (100)
D80
individual measurements on isolated failures
since recommendations in the report will be to
replace these failures.
Where:
**
(D − x ) is the difference between each
i
PRD = Percent Reduction in
individual measurement and the mean value. Deflection required at the surface
The number of measurements is designated n.
4-1
______________________________________________________________________________________
TDS = Tolerable Deflection at the Ten-Year 80th Percentile Existing Structural

Surface, in inches TI Deflection Section
10.0 0.030 inch 0.55 foot AC
D80 = 80th Percentile of the 0.50 foot AB
Deflections at the Surface for a 1.00 foot AS
test section in inches. If test
sections have been grouped, then Existing conditions:
average D80 for the group is used. • Occasional to intermittent alligator,
transverse, and longitudinal cracks,
6. Determine the increase in Gravel (some 0.5 inch wide).
Equivalence (GE) required to reduce D80
to the TDS. Utilizing the calculated • Fairly smooth ride.
PRD value, go to Table 2, Column A, to
determine the GE. (Discussion of an AC
overlay placed on a cushion course is in Calculations 4-1:
Section 4-70.)
Check for overlay thickness required
7. Determine the Gravel Factor, Gf. For for structural adequacy.
a dense graded asphalt concrete (DGAC)
overlay over an existing AC pavement Step 1:
use a Gf of 1.9 regardless of thickness Obtain tolerable deflection at the
and TI. surface (TDS).
Use Table 1:
8. Determine the overlay thickness for AC = 0.55 ft and TI = 10.0
structural adequacy. TDS = 0.012 inch
GE
overlay = Step 2:
Gf
Compare average D80 to TDS.
9. Determine the overlay thickness for 0.030 > 0.012
reflective cracking.
Stem 3:
overlay = A minimum of half of Calculate Percent Reduction in
the existing AC Deflection required.
thickness (Section 3-20)
 0.030 − 0.012 
10. Determine the overlay thickness for  (100) = 60%
 0.030 
ride quality.
overlay = A minimum of 0.25 ft Step 4:

placed in two layers Determine Gravel Equivalence
(Section 3-30) (GE) required for deflection
reduction.
Use Table 2; Column A
Example 4-1: Determine the GE = 0.85 ft
recommended AC overlay thickness for
an existing AC pavement.
4-2
______________________________________________________________________________________
Step 5: • For this overlay example, reflective

Determine the required thickness cracking could never control, since
of AC overlay for structural the structural requirement of 0.45 ft
adequacy. (135 mm) is already above the 0.35-
ft (105-mm) maximum for reflection.
GE 0.85
Overlay = = = 0.45 ft
Gf 1 .9 • In this example, if the structural
requirement had been less than 0.30
ft (90 mm) and the ride quality
Check for the overlay thickness needed improvement, then reflective
required for reflective crack cracking would be the controlling
retardation. criteria with a required overlay of
0.30-ft (90-mm).
To retard reflective cracks entering the
new overlay from the pavement below • To make a rough-riding pavement
choose a thickness for the new overlay at smoother by using a minimum of
least one-half the thickness of the two procedures, a mill-and-replace
existing AC pavement being overlaid procedure or a procedure that places
(up to a maximum of 0.35 ft (105 mm) an AC overlay in two layers must be
for an underlying aggregate base). used. The design of the overlay for
ride consideration would be as
Determine half of the existing pavement follows:
thickness:
Option 1 - The overlay must be
0.55 thick enough to allow for two
overlay = = 0.275 Round layers to be placed. The 0.45-ft
2
(135-mm) DGAC overlay for
to 0.30 ft.
structural adequacy will provide
the two layers needed for
improving the ride quality.
Check for smoothness.
Option 2 - Mill the existing
The ride quality was previously
rough pavement to remove much
determined to be acceptable. If it were
of the surface undulations prior
not acceptable, a 0.25-ft (75-mm)
to placing the new AC overlay.
DGAC overlay would have to be placed
Milling off 0.10 to 0.20 ft (30 to
in two layers.
60 mm) will usually be
sufficient. Milling will change
D80 and require additional design
Discussion 4-1:
calculations.
• Since reflective cracking
requirement is less than 0.45 ft (135- Recommendation 4-1: 0.45-ft (135-mm)
mm), and since smoothness is overlay of DGAC.
satisfactory, structural adequacy
governs the overlay design thickness.
4-3
______________________________________________________________________________________
4 – 20 Rubberized Asphalt Concrete A Rubberized Stress Absorbing

(Type G) * Membrane Interlayer (SAMI-R) may be
used to provide some strength when
Caltrans standard overlay design is a placed under RAC Type G. For
dense graded asphalt concrete overlay structural strength, a SAMI-R is
thickness that will improve the considered to provide an equivalence of
serviceability for the time frame 0.05 ft (15 mm) of RAC Type G (Table
specified, usually a ten-year period. 3). For reflective crack retardation from
From that design thickness an alternate wide cracks, the SAMI-R is considered
design with a thickness of rubberized to provide either 0.05 ft (15 mm) when
asphalt concrete, gap graded (RAC Type the underlying base is a treated material
G) can be determined. or 0.10 ft (30 mm) when the underlying
base is an untreated material (Table 4).
A thickness equivalency of not more However, it should be noted that RAC
than 1:2 is given to the RAC Type G Type G might not prevent cold weather
when compared to the dense graded cracking. A Fabric Stress Absorbing
asphalt concrete (DGAC) for structural Membrane Interlayer (SAMI-F) is not to
adequacy or reflective crack retardation. be used under RAC Type G because the
The equivalencies are tabulated in high placement temperature of the RAC
Tables 3 and 4 Type G is close to the melting
temperature of the SAMI-F material.
Using RAC Type G instead of DGAC
allows a lower profile grade and reduces Just as with DGAC, prior to placement
the amount of asphalt concrete materials of RAC Type G on an existing
used. pavement, some preparation is required.
Cracks wider than 0.25 inch (5 mm)
The minimum thickness for RAC Type should be sealed, and potholes and
G is 0.10 ft (30 mm). Until further localized failures repaired.
research, the maximum thickness For
RAC Type G is limited by stability to It is undesirable to place RAC Type G in
0.20 ft (60 mm). If the design calls for a areas that will not allow surface water to
thicker overlay, then a DGAC layer may drain. As an example, on a surface that
be placed prior to placing the RAC Type is milled only on the traveled way and
G. For example, if the design calls for a not on the shoulders, thus forming a
0.55-ft (165-mm) DGAC overlay, a “bathtub” section. To offset that
0.15-ft (45-mm) layer of DGAC could situation, a combination of materials
be placed first. Then the 0.40-foot (120- might fit the design; for example, place a
mm) DGAC remaining can be replaced layer of DGAC to the original grade
with 0.20-ft (60-mm) of RAC Type G prior to placing the RAC Type G, or mill
placed as the top layer (Table 3). the shoulders to slope for drainage.
* Data from field and laboratory studies were

used to produce Caltrans internal memorandum
“Asphalt Rubber Hot Mix – Gap Graded
Thickness Determination Guide” dated March
19, 1992.
4-4
______________________________________________________________________________________
4 – 30 Stress Absorbing Membrane

Interlayers Moisture trapped within the asphalt
concrete, under wheel loads, may
provide a means by which the asphalt
Two types of Stress Absorbing
would be washed off the aggregates.
Membrane Interlayers are used for
This action is called stripping. Some
rehabilitation:
mixes are more susceptible to this action
than others. When AC is to be placed in
1.) Rubberized (SAMI-R).
these types of locations the aggregates
2.) Fabric (SAMI-F).
should be treated prior to mixing.
Placing a rubberized stress absorbing
A SAMI may be placed between layers
membrane interlayer on a pavement
of new asphalt concrete (AC), such as on
consists of an application of asphalt-
a leveling course, or on the surface of an
rubber binder on the surface followed
existing AC pavement. When placed on
with aggregate screenings that are pre-
an existing AC pavement some
coated with paving asphalt.
preparation is required to prevent excess
stress on the membrane. This includes
Placing a fabric stress absorbing
sealing cracks wider than 0.25 inch (5
membrane interlayer on a pavement
mm), and repairing potholes and
consists of an application of asphalt
localized failures.
binder on the surface followed with the
fabric. The fabric is manufactured from
polyester, polypropylene or
SAMI-R:
polypropylene-nylon material that is
non-woven and heat treated on one side.
Placed Under Rubberized Asphalt
See Standard Specifications 39-4.03.
Concrete
SAMI’s are used to retard reflective
Structural Strength – A SAMI-R also
cracks, prevent water intrusion, and in
may be used to provide some structural
the case of SAMI-R, enhance structural
strength when placed under an RAC
strength (Table 3).
Type G overlay that is designed for
structural adequacy. The SAMI-R in
Judgment is required when considering
this case is considered to be
the use of SAMI’s.
approximately 0.05 ft (15 mm) of RAC
Type G for structural strength (Table 3).
• Consideration should be given to
areas that may prohibit surface water
Reflective Cracking – A SAMI-R is
from draining out the sides of the
considered to be equivalent to 0.05 ft (15
overlay, thus forming a “bathtub”
mm) of RAC Type G when the
section.
underlying base of the structural section
is a treated base. When the underlying
• Since SAMI’s act as a moisture base is an untreated base, a SAMI-R is
barrier, they should be used with equivalent to 0.10 ft (30 mm) of an RAC
caution in hot environments where Type G (Table 4).
they could prevent underlying
moisture from evaporating.
4-5
______________________________________________________________________________________
leveling course of DGAC prior to the

Placed Under Non-Rubberized Asphalt placement of the SAMI-F.
Concrete
Saturating the fabric with asphalt
When a SAMI-R is placed under non- enhances the properties of the pavement
rubberized asphalt concrete designed for reinforcing fabric. The fabric is placed
reflective crack retardation, the on the asphalt concrete pavement that
equivalence of a SAMI-R depends upon has had a heavy tack coat of asphalt
the type of base material under the applied. However, on a cool day the
existing pavement. When the base is a tack coat may cool rapidly, until it
treated material, a SAMI-R placed under reaches the temperature of the pavement.
DGAC or open graded asphalt concrete In this case, the tack asphalt usually will
(OGAC) is considered to be equivalent remain tacky enough to hold the fabric
to 0.10 ft (30 mm) of DGAC. When the in place, but full saturation will not
base is an untreated material SAMI-R is occur. Therefore, it is up to the heat of
equivalent to 0.15 ft (45 mm) of DGAC. the asphalt concrete overlay to re-melt
the tack coat, allowing it to infiltrate the
fabric. With normal heat and rolling
SAMI-F: pressure of the first layer of asphalt
concrete, the fabric should become
A Fabric Stress Absorbing Membrane saturated. On warm days, the fabric may
Interlayer (SAMI-F), also called come close to full saturation just by
pavement reinforcing fabric (PRF), lying on the asphalt tack coat because
placed under DGAC designed for the asphalt stays liquid longer.
reflective crack retardation provides the
equivalent of 0.10 ft (30 mm) of DGAC. SAMI-F’s have been found to be
This allows the project engineer to ineffective:
decrease the new profile grade and also 1.) When placed under asphalt rubber-
save asphalt concrete materials. asphalt concrete. This is due to the high
placement temperature of the RAC Type
If the road to be rehabilitated has a high G mix, which is close to the melting
proportion of small radius horizontal temperature of the fabric.
curves, the use of SAMI-F is probably 2.) For providing added structural
not cost effective due to the extra labor strength when placed in combination
involved during placement. with DGAC.
3.) In the reduction of thermal cracking
of the new AC pavement overlay.
A SAMI-F should not be placed directly
on coarse surfaces such as a chip seal,
OGAC, areas of numerous rough patches
4 – 40 Cold Recycled Asphalt
or on a pavement that has been cold
Concrete Pavement
planed. Coarse surfaces may penetrate
the fabric and/or the paving asphalt
Assembly Bill (AB 1306) encourages
binder used to saturate the fabric may be
State agencies to use more recycled
“lost” in the voids or valleys leaving
materials in road construction and
areas of the fabric dry. For the SAMI-F
repairs. Caltrans Deputy Directive DD-
to be effective in these areas, use a
4-6
______________________________________________________________________________________
17 policy statement, effective November thicknesses will have slight variations,

11, 1993, directs the Department to the cold recycling design should leave at
recycle asphalt concrete whenever least the bottom 0.15 ft (45 mm) of the
feasible. Consideration should be given existing AC pavement in place. This is
on every project to recycle asphalt to insure the milling machine does not
concrete (AC) used in highway loosen base material and possibly
construction, maintenance, and contaminate the CRAC mix design.
rehabilitation projects utilizing the
Department’s priority hierarchy (see Traffic constraints may make CRAC
DD-17). Public and employee health impractical since traffic is not allowed
and safety are not to be compromised by on the lane being recycled until the
recycling AC on any project. To be process is completed and the recycled
economical on rehabilitation projects, a material is compacted.
minimum of 10,000 tons (9070 tonnes)
of AC material should be available for The recycling process consists of the
the recycle process. In the future, following:
calculations using the then current price
of asphalt material may change the 1. Mill the existing AC pavement to the
quantity for the minimum tons to be designed depth.
economical. 2. Mix the milled material with an oil
or rejuvenating agent and leave in a
Since this design method uses two windrow.
procedures (milling and replacement), it 3. The CRAC material is then spread
can be considered appropriate to smooth with a paving machine and
a rough pavement. compacted.
Candidates for cold recycling are The surface of the CRAC material has a
pavements whose asphalt content is low resistance to abrasion. Therefore,
uniform. The existence of heavy crack- all CRAC material must be covered with
sealant, numerous patches, open-graded a minimum thickness of 0.15 ft (45 mm)
asphalt concrete, and heavy seal coats DGAC for a wearing surface after a
make the new Cold Recycled Asphalt short period of time after the recycling
Concrete (CRAC) mix design process.
inconsistent. Mix properties are more
difficult to control. To avoid this When designing the CRAC for structural
problem when it occurs and still use this adequacy, the Tolerable Deflection at the
recycle option, a minimum of 0.08 ft (25 Surface (TDS) is always determined
mm) should be milled off prior to the using the thickness of the existing
cold recycling operation. Light crack pavement prior to milling. The
sealing (less than 5 % of the pavement) additional Gravel Equivalence (GE)
or a uniform single seal coat will not required to reduce the measured
influence the design sufficiently to deflection to the tolerable level in the
require removal. cold recycling design is a combination
of:
Caltrans has established a minimum mill
depth of 0.15 ft (45 mm) for cold
recycling. Since existing pavement
4-7
______________________________________________________________________________________
• The GE determined from the basic or analytical depth will be reached, a

overlay calculations, and trial and error or iterative type of
• The GE required to replace the calculation is required.
material removed by the milling
process. Using the thickness of the existing AC
pavement and the design TI, determine
The analysis must first consider milling the TDS from Table 1. The deflection at
down to no more than what Caltrans the milled depth is found from the
calls the “analytical depth”. * equation:
Use the following definitions for CRAC   MillDepth  

analysis: DM = D80 + (12% ) (D80 )
  0.10 ft  
Mill Depth = The depth of the milling in
feet. The PRM is then found:
 DM − TDS 
D80 = 80th Percentile of the deflections at PRM =  (100)
 DM 
the surface in inches, for a test section.
DM = The calculated Deflection at the Utilizing the calculated PRM value as

Milled depth in inches. percent reduction in deflection, go to
Table 2, Column A, to get the total GE
required to be placed on top of the
  MillDepth  
DM = D80 + (12% ) (D80 ) milled pavement surface. Using the total
  0.10 ft   GE requirement and subtracting the GE
of the CRAC thickness, (CRAC
TDS = Tolerable Deflection at the thickness times 1.5) the thickness of the
Surface in inches. DGAC cap is determined. The Gf for
CRAC is 1.5 and for DGAC the Gf is
PRM = Percent Reduction in deflection 1.9.
required at the Milled depth.
GE of DGAC = (Total GE required) –
 DM − TDS  (CRAC thickness)(1.5)
PRM =  (100)
 DM  Thickness of DGAC = GE of DGAC/1.9
The percent reduction in deflection at the If the milling goes below the analytical
milled depth is based on a research study depth, the analysis changes. Rather than
that determined deflections increase by increasing the deflections, the analysis
12% for each additional 0.10 ft (30 mm) assigns a Gf of 1.4 to the material below
of milled depth. (7) Since it is not known the analytical depth.
at what milled depth the 70% PRM level
Therefore, the additional GE that is
*
The “analytical depth,” as defined by Caltrans, required to replace this lower portion of
is the milled depth at which the required Percent the milled pavement is:
Reduction in Deflection (PRM) reaches 70%, or
the milled depth reaches 0.50 ft (150 mm),
whichever comes first.
4-8
______________________________________________________________________________________
Additional GE = [(1.4)(milled depth Reflective Cracking:

below the analytical depth)] A 0.30-ft DGAC overlay. (One-
half existing AC thickness.)
This additional GE is added to the total
GE determined to be placed on top of the Ride Quality:
milled pavement surface at the analytical A 0.25-ft DGAC overlay placed
depth. in two layers. (Section 3-30).
Finally, a determination is made to see if Use Table 1 to determine that the TDS is
the designed thicknesses of the CRAC 0.017 inch
and DGAC are suitable. For CRAC to be
considered, it must be cost-effective. Calculation 4-2:
Items to consider are: Start with a minimum milling depth of
0.15 ft and find the deflection at the
• The increase in the profile grade milled depth:
should be at least 0.10 ft (30 mm)
less than the increase from the basic
overlay design; otherwise a basic DM = D80 + (12% ) (D80 )
overlay would be less costly; and   0.10 ft  
• The amount of CRAC material
should be about 10,000 tons (9070 DM = (0.030 inch)+[(1.2/ft)(0.15
tonnes) or more to be cost effective. ft)(0.030 inch)] = 0.035 inch
For CRAC design, it is recommended to Determine the Percent Reduction in

round up to get the CRAC and DGAC Deflection at the Milled Depth (PRM):
thicknesses.
 DM − TDS 
PRM =  (100)
Example 4-2: Determine the cold-  DM 
recycled thickness and the DGAC cap
thickness for rehabilitation. PRM = [(0.035 inch – 0.017 inch)/0.035
inch](100)
Ten-Year 80th Percentile Existing Structural PRM = 51.0% < 70 %, the analytical
TI Deflection Section depth.
8.0 0.030 inch 0.55 foot AC Therefore, use PRM = 51%
0.50 foot AB
1.00 foot AS From Table 2, Column A, the total GE
required is 0.66 ft.
Solution 4-2:
GE of CRAC = (0.15 ft)(1.5) = 0.22 ft
Structural Adequacy: Determine the GE that the DGAC
A 0.30-ft DGAC overlay. Refer overlay has to provide:
to Example 3-1. (Rubber AC GE of DGAC = Total GE required – GE
alternatives are discussed in of CRAC = 0.66 ft – 0.22 ft = 0.44 ft.
Section 4-20 of this manual.)
Thickness of DGAC = 0.44 ft/1.9
4-9
______________________________________________________________________________________
= 0.23 ft. Round up to 0.25 ft. 56.4% < 70%, the analytical depth.
This is not acceptable since the DGAC
thickness saved from the basic overlay is Therefore, use PRM = 56.4%
only (0.30 ft – 0.25 ft ) = 0.05 ft. This
should be at least 0.10 ft.
Try again. From Table 2, Column A, the total GE
Trial 2: Increase the milling depth to
0.20 ft and find the deflection at the GE of CRAC = (0.25 ft)(1.5) = 0.38 ft
milled depth:
GE of DGAC = Total GE required – GE
DM = (0.030 inch) + [(1.2/ft)(0.20 ft) of CRAC = 0.77 ft – 0.38 ft = 0.39 ft
(0.030 inch)] = 0.037 inch
Thickness of DGAC = 0.39 ft/1.9 = 0.21
PRM = [(0.037 inch – 0.017 inch)/0.037 ft. Round up to 0.25 ft.
inch ](100) = 54%
Again the results did not change for the
54% < 70%, the analytical depth. DGAC thickness saved from the basic
overlay. This should be at least 0.10 ft.
Therefore, use PRM = 54% Try again.
From Table 2, Column A, the total GE Trial 4: Increase the milling depth to
required is 0.72 ft. 0.30 ft and find the deflection at the
milled depth:
GE of CRAC = (0.20 ft)(1.5) = 0.30 ft
DM = (0.030 inch) + [(1.2/ft)(0.30 ft )
GE of DGAC = Total GE required – GE (0.030 inch)] = 0.041 inch
of CRAC
PRM = [(0.041 inch – 0.017 inch)/0.041
= 0.72 ft – 0.30 ft = 0.42 ft inch](100) = 58.5%
Thickness of DGAC = 0.42 ft/1.9 = 0.22 58.5 < 70%, the analytical depth.
ft. Round up to 0.25 ft.
Therefore, use PRM = 58.5%
The results did not change for the
DGAC thickness saved from the basic From Table 2, Column A, the total GE
overlay. This should be at least 0.10 ft. required is 0.82 ft.
Try again.
GE of CRAC = (0.30 ft )(1.5) = 0.45 ft
Trial 3: Increase the milling depth to
0.25 ft and find the deflection at the GE of DGAC = Total GE required – GE
milled depth: of CRAC = 0.82 ft – 0.45 ft = 0.37 ft
DM = (0.030 inch) + [(1.2/ft)(0.25 ft) Thickness of DGAC = 0.37 ft/1.9 = 0.19

(0.030 inch)] = 0.039 inch ft. Round up to 0.20 ft.
PRM = [(0.039 inch – 0.017 inch)/0.039

inch](100) = 56.4%
4-10
______________________________________________________________________________________
Discussion 4-2: 4 – 50 Hot Recycled Asphalt Concrete

Pavement
When compared to the basic overlay
design, CRAC saves 0.10 ft of virgin Assembly Bill (AB 1306) encourages
DGAC and would also decrease the final State agencies to use more recycled
profile grade of the shoulder thus saving materials in road construction and
shoulder-backing material. repairs. Caltrans Deputy Directive DD-
17 policy statement, effective November
Now that the first consideration has been 11, 1993, directs the department to
met, consider volume. For a project 10 recycle asphalt concrete (AC) whenever
miles long and pavement 24 feet wide feasible. Consideration should be given
would this produce enough CRAC on every project to recycle AC used in
material to be cost effective? Assuming highway construction, maintenance, and
a compacted AC density of 145 pcf, the rehabilitation projects utilizing the
milling tonnage is calculated as [(10 Department’s priority hierarchy (see
miles)(5280 ft/mile) (24 ft)(0.30 ft)(145 DD-17). Public and employee health
lbs/cu ft)]/2000 lbs/ton = 27,562 tons. and safety are not to be compromised by
This is greater than 10,000 tons, the recycling AC on any project. At the
minimum required, and thus is present time, to be economical on
acceptable. By reducing the overlay by rehabilitation projects, a minimum of
0.10 ft, a saving of 9,187 tons of new 10,000 tons (9070 tonnes) of AC
material or natural resources would be material should be available for the
accomplished. [In this example, milling recycle process. In the future,
did not go below the analytical depth – it calculations using the then-current price
reached 58.5% compared to the of asphalt material may change the
maximum of 70%, and the depth was quantity for the minimum tons to be
less than 150 mm (0.50 ft) of milling.] economical for Hot Recycled Asphalt
(See Hot Recycled Asphalt Concrete Concrete (HRAC).
Pavement design for an example of an
analysis with milling below the Since this design method uses two
analytical depth.) procedures (milling and replacement), it
is one that can be considered appropriate
Cold recycling is, therefore, an to smooth a rough pavement.
acceptable recommendation because it
decreases the final overlay profile grade The hot recycling operation consists of
thus saving virgin DGAC and shoulder the following:
backing, and it has over 10,000 tons of
recycled material making it cost 1. Mill the existing AC to obtain the
effective for this project to bring in the Reclaim Asphalt Pavement (RAP).
specialized equipment. 2. Haul the RAP to an asphalt mixing
plant. *
Recommendation 4-2: Cold recycle 0.30
ft (90 mm) of the existing pavement and
cap with 0.20 ft (60mm) of DGAC. *
This is not hot-in-place recycling (surface
recycling) which is a maintenance procedure.
Hot-in-place recycling material does not leave
the pavement lane site.
4-11
______________________________________________________________________________________
3. Add the RAP and oil or rejuvenating allowed on the pavement prior too the
agent to the new DGAC mix to HRAC material being placed and
obtain the recycled mix. compacted. The thin remaining surface,
4. Haul the HRAC mix back to the if opened to traffic, would cause
project to be spread with a paving degradation of the pavement and affect
machine and then compacted. the design life of the new HRAC
5. To prevent damage, traffic should be material.
minimized or not allowed on the
milled surface of the lane being When designing the HRAC for structural
recycled depending on the thickness adequacy, the tolerable deflection (TDS)
of AC pavement remaining after is always determined using the thickness
milling (must be at least 0.25 ft left of the existing pavement. In a hot
before allowing any traffic on the recycling design, the additional GE
lane). required to reduce the measured
deflection to the tolerable level is a
Pavements that are candidates for hot combination of:
recycling are those with uniform asphalt
content. The existence of heavy crack- • The GE required from the basic
sealant, numerous patches, open-graded overlay calculations, and
asphalt concrete, and heavy seal coats • The GE required to replace the
make the new Hot Recycled Asphalt material removed by the milling
Concrete (HRAC) mix design machine.
inconsistent and therefore more difficult
to control the mix properties. To avoid The percent reduction in deflection at the
this problem when it occurs and still use milled depth is based on a research study
this recycle option on projects, a that determined that deflections increase
minimum of 0.08 ft (25 mm) should be 12% for each additional 0.10 ft (30 mm)
milled off and stockpiled for other uses of milled depth (7).
(e.g., shoulder backing) prior to the hot
recycling operation. Light crack sealing Since it not known at what milled depth
(less than 5 % of the pavement) or a the 70 % PRM level or the “analytical
uniform single seal coat will not depth*” will be reached, this is a trial and
influence the design sufficiently to error or iterative type of calculation.
require removal.
Use the following definitions for HRAC
Caltrans has established a minimum mill analysis:
depth of 0.10 ft (30 mm) for hot
recycling. Since existing pavement Mill Depth = The depth of the milling in
thicknesses will have slight variations feet.
the hot recycling design should leave at
least the bottom 0.15 ft (45 mm) of the
existing AC pavement in-place. This is
*
to insure the milling machine does not The analytical depth, as defined by Caltrans, is
loosen base material and possibly the depth the required Percent Reduction in
Deflection at the milled depth reaches 70%, or
contaminate the HRAC mix design.
the milled depth reaches 0.50 ft (150 mm),
Milling down to a depth that leaves only whichever comes first. For discussion of deeper
0.15 ft works only when traffic is not milling depths see Remove and Replace.
4-12
______________________________________________________________________________________
D80 = 80th Percentile of the deflections at the Gf of 1.4. The additional GE that is
the surface in inches, for a test section. required to replace the portion below
analytical depth is calculated by
DM = The calculated Deflection at the multiplying the Gf of 1.4 by the milled
Milled depth in inches. depth below the analytical depth. This is
added to the required GE to be placed on
  MillDepth   top of the milled surface at the analytical
DM = D80 + (12% ) (D80 )
 0.10 ft  depth. The total HRAC thickness
 
required is found by dividing the sum of
the two GE’s by the Gf of 1.9.
TDS = Tolerable Deflection at the
Surface in inches. Finally, a determination is made to see if
the designed thickness of the HRAC is
PRM = Percent Reduction in deflection
suitable. For HRAC to be considered, it
must be cost effective. Items to consider
are:
 DM − TDS 
PRM =  (100)
 DM  • The increase in the profile grade
should be at least 0.10 ft (30 mm)
Using the thickness of the existing AC less than the increase from the basic
pavement and the design TI, determine overlay design; otherwise a basic
the TDS from Table 1. Calculate the overlay would be less costly; and
deflection at the milled depth from the
equation: • The amount of RAP should be about
10,000 tons (9070 tonnes) or more to
  MillDepth   be cost effective.
DM = D80 + (12% ) (D80 )
  0.10 ft   Unlike cold recycled material, HRAC
pavement can be used as a surface
The PRM is then found: course without a DGAC cap. The Gf of
HRAC is the same as DGAC (i.e., Gf =
 DM − TDS 
PRM =  (100) 1.9 ). Therefore, this analysis can also
 DM  be used for DGAC on milled pavement
and the reclaimed asphalt pavement
could be stockpiled for future use.
Utilizing the calculated PRM value go to
Table 2, Column A, to get the total GE
required to be placed on top of the Example 4-3: Determine the milling
milled pavement surface. The HRAC depth and the hot-recycled thickness for
thickness is found by dividing the GE by rehabilitation.
the Gf of 1.9.
Ten-Year 80th Percentile Existing Structural
If the milling goes below the analytical TI Deflection Section
depth, the analysis changes. The 11.0 0.031 inch 0.75 foot AC
existing material below the analytical 0.50 foot AB
depth is considered to be of questionable 1.00 foot AS
structural integrity and hence assigned
4-13
______________________________________________________________________________________
Solution 4-3: From Table 2, Column A, the total GE

Structural Adequacy: Find the HRAC thickness:
A 0.50-ft DGAC overlay. Refer GE/Gf = 1.06 ft/1.9 = 0.56 ft. Round to
to Example 3-1. (Rubber AC 0.55 ft.
alternatives are discussed in
Section 4-20 of this manual.) The increase in grade is (0.55 ft – 0.15
ft) = 0.40 ft. This is acceptable since the
Reflective Cracking: reduction in profile grade from the basic
A 0.35-ft DGAC overlay. (One- overlay is 0.10 ft. This would save 0.10
half existing AC thickness with a ft of virgin DGAC and would also
maximum of 0.35 ft.) decrease the final grade of the shoulder
thus saving shoulder-backing material.
Ride Quality:
A 0.25-ft DGAC overlay placed The quantity for milling 0.15 ft in two
in two layers. (Section 3-30). lanes per mile is calculated as follows:
[(1 mile)(5280 ft/mile)(24 ft)(0.15

Use Table 1 to determine that the TDS is ft)(145 lbs/cu ft)]/2000 lbs/ton = 1,378
0.011 inch. tons. The project should be long enough
(and/or wide enough) to provide at least
Calculation 4-3: Start with a milling 10,000 tons for recycling. 10,000
depth of 0.15 ft and find the deflection at tons/1,378 tons per mile = 7.3 miles.
the milled depth
The percentage RAP in the mix is (0.15
  ft milled/0.55 ft HRAC thickness)(100)
 MillDepth 
DM = D80 + (12% ) (D80 ) = 27%. In order to get more RAP and
  0.10 ft   use less virgin material, the milling
depth should be increased.
DM = (0.031 inch) + [(1.2/ft)(0.15
ft)(0.031 inch)] = 0.037 inch Since the analytical depth was nearly
reached (69.9%) at the milled depth of
Determine the Percent Reduction in 0.15 ft, all milled and removed material
Deflection at the Milled Depth (PRM): below that level will be considered to be
material with a Gf of 1.4.
 DM − TDS 
PRM =  (100) Trial 2: Increase the milled depth to
 DM 
0.25 ft (0.10 ft below the analytical
depth) to save more material.
PRM = [(0.037 inch – 0.011 inch)/0.037 Total thickness of the HRAC = [(GE
inch](100) required at 0.15 ft milled depth) + (GE
required due to additional milling)]/1.9.
PRM = 69.9% ≈ 70%, the analytical
depth. HRAC = [(1.06 ft) + (0.10 ft)(1.4)]/1.9
= 0.63 ft of HRAC. Round to 0.65 ft.
Therefore, use PRM = 69.9%
4-14
______________________________________________________________________________________
The percent of RAP is (0.25 ft/0.65 study has shown that deflections will
ft)(100) = 38 %. increase an average of 12% for each
0.10-ft of pavement milled off (based on
Trial 3: Increase the milled depth to milling depths down to about 0.50 ft).(7)
0.30 ft (0.15 ft below the analytical The greater the depth of milling the less
depth) to save more material. accurate the determination may be of the
calculated deflections.
HRAC = [(1.06 ft) + (0.15 ft)(1.4)]/1.9
= 0.67 ft. Round to 0.65 ft. R&R design from deflections is also less
reliable if a bulldozer or a scraper is used
The percent of RAP is (0.30 ft/0.65 to remove the material under the
ft)(100) = 46 %. pavement instead of a milling machine.
This method of removing material
Discussion 4-3: disturbs the integrity of the in-place
At this milling depth the RAP content is material from which the deflections were
46% and the increase in grade is 0.35 ft. measured.
This will save 0.15 ft of new material
compared with the 0.50 ft DGAC The alternative to the use of this design
overlay needed by the basic overlay and is the R-value design method (see HDM
would also decrease the final grade of Chapter 600).
the shoulder thus saving shoulder-
backing material. When using the R&R method in
designing for structural adequacy, the
Recommendation 4-3: Mill 0.30 ft (90 tolerable deflection (TDS) is always
mm) of the existing pavement and then determined using the thickness of the
replace it with a total thickness of 0.65 ft existing pavement.
(195 mm) of HRAC.
The analysis used for R&R is similar to
the HRAC analysis (Section 4-50). First
4 – 60 Remove and Replace consider milling down to what is called
the analytical depth. This is the depth
When it is not possible to maintain the where the required Percent Reduction in
existing profile grade using the hot Deflection at the Milled depth (PRM)
recycled hot mix (HRAC) design, the reaches 70% or to 0.50 ft (150 mm), or
remove-and-replace strategy can be to the bottom of the pavement,
used. The Remove-and-Replace (R&R), whichever comes first. As discussed
sometimes called Mill and Fill, operation above, the 70% PRM is based on an
consists of milling the entire AC increase in deflection of 12% for each
pavement and possibly into the base 0.10-ft (30 mm) of milled pavement.
material. (When using several milling This is an iterative type of calculation
passes, part of the AC may be used to since it not known at what milling depth
reclaim asphalt pavement for HRAC.) the 70% level will be reached. Use the
The entire milled depth is then replaced following definitions for the R&R
with DGAC or HRAC. analysis:
This design method may be less reliable Mill Depth = The depth of milling in
the deeper the milling is performed. A feet.
4-15
______________________________________________________________________________________
D80 = 80th Percentile of the deflections at GE = (Gf)(thickness of the layer milled)

the surface in inches, for a test section.
DM = The calculated Deflection at the Commonly Used Gf for Rehabilitation

Milled depth in inches.
Asphalt Concrete 1.9
DM = D80 + (12% ) (D80 ) Hot Recycled
  0.10 ft   1.9
Asphalt Concrete
TDS = Tolerable Deflection at the Cold Recycled
Surface in inches. 1.5
Asphalt Concrete
PRM = Percent Reduction in deflection Treated Base 1.5
AC Below the
 DM − TDS  1.4
PRM =  (100) Analytical Depth
 DM 
Aggregate Base 1.1
Use the thickness of the existing AC
pavement and the design Traffic Index Aggregate
1.0
(TI) in Table 1 to determine the Subbase
Tolerable Deflection at the Surface
(TDS). Then find the deflection at the Native Soil 0
milled depth.
The existing base material is considered
DM = D80 + (12% ) (D80 ) treated if it meets all of the following
  0.10 ft   conditions:
The percent reduction in deflection at the • Its depth is equal to or greater

milled depth (PRM) is then found: than 0.35 ft (105 mm).
 DM − TDS  • The D80 is less than 0.015 inch.*

PRM =  (100)
 DM 
• It was portland cement concrete
(PCC), lean concrete base
Utilizing this calculated PRM value go
(LCB), or Class A cement
to Table 2, Column A to get the GE
treated base (CTB-A) when first
required to be placed on top of the
installed.
milled surface. When the milled depth
reaches the analytical depth, the analysis
changes. The GE for the material milled The replacement DGAC thickness is
out below the analytical depth is added found by dividing the sum of the GE’s
to the GE required at the analytical by the Gf of the new DGAC. For the
depth. The GE for each layer is
calculated by: *
See discussion in Section 3 – 10.
4-16
______________________________________________________________________________________
R&R design method, use the Gf for the DGAC overlay thickness = (1.06
new DGAC commensurate with the TI ft)/(1.9) = 0.56 ft. Round to 0.55 ft.
and AC thickness found in Table 608.4
of the Highway Design Manual Reflective Cracking:
(HDM).*(8) The total DGAC thickness A 0.35-ft DGAC overlay. (One-half
can be solved for each 0.05 ft (15 mm) existing AC thickness with a
of material milled until the desired maximum of 0.35 ft.)
profile is reached. Round the
replacement thickness to the nearest 0.05 Ride Quality:
ft. A 0.25-ft DGAC overlay placed in
two layers. (Section 3-30).
Example 4-4: Determine the milling
depth and the DGAC thickness for Calculation 4-4: Now provide a
rehabilitation to maintain the existing rehabilitation strategy by the R&R
profile grade. method that maintains the existing
profile grade.
TI Deflection Section In this example, the analytical depth of
12.0 0.030 inch 0.75 foot AC 70% was reached at the surface, so to
0.50 foot AB obtain the GE below the surface, all the
0.83 foot AS
calculations will be multiplying the Gf
times the thickness of the layer milled.
These values will then be added to the
Solution 4-4:
GE required at the surface.
Find the GE removed when milling from
the analytical depth (the surface in this
example) down to the bottom of the
pavement: GE = (0.75 ft)(1.4) = 1.05 ft.
Solve for a basic DGAC overlay.
Use Table 1 to find that the TDS is This is added to the GE at the surface
0.009 inches. and divided by the Gf of the new DGAC
to get the thickness required: (1.06 ft) +
PRD = [(0.030 inches – 0.009 (1.05 ft) = 2.11 ft GE.
inches)/0.030 inches](100) = 70.0 %
This is a trial and error problem since the
Gf that matches the new DGAC
Use Table 2, Column A, to thickness is unknown at this time.
determine that 1.06 ft is the increase Assume a Gf of 1.9. (This is usually a
in GE required to reduce the D80 to good starting point since it is about the
the tolerable deflection level. middle of Table 608.4).
GE/Gf = (2.11 ft)/1.9 = 1.11 ft of

DGAC. Round to 1.10 ft.
*
For an AC thickness greater than 0.50 ft (150
mm), the Gf increases as the thickness increases; From Table 608.4 of the HDM, the Gf =
see HDM Index 608.4 (8). 2.09 for a thickness of 1.10 ft.
4-17
______________________________________________________________________________________
Calculate the replacement thickness pavement, is one way that sometimes

using the Gf of 2.09 for the 1.10-ft. The works to estimate the needed additional
DGAC thickness is: depth below the pavement.
GE/Gf = (2.11 ft)/(2.09) = 1.01 ft. [(1.9)/(1.1)](0.30 ft) = 0.52 ft. Round
Round to 1.00 ft of DGAC. to 0.50 ft.
To match the thickness for which the Gf This would be a total depth of 1.25 ft
is used, the answer appears to be (0.75 ft + 0.50 ft).
between 1.00 ft and 1.10 ft. Assuming a
thickness of 1.05, the Gf is equal to 2.05 Find the GE value of the AB removed to
(HDM, Table 608.4) and thus the DGAC the estimated depth (0.50 ft):
thickness needed is:
GE = (0.50 ft)(1.1) = 0.55 ft.
GE/Gf = (2.11 ft)/(2.05) = 1.03 ft.
This is added to the GE’s at the
Round to 1.05 ft of DGAC. (This analytical depth and bottom of the
matches the thickness for which the Gf pavement, and then divided by the Gf of
was used.) the DGAC to yield the required
thickness:
When the milling extends to the bottom
of the pavement (0.75 ft ), the removed GE = (1.06 ft) + (1.05 ft) + (0.55 ft) =
material is replaced with 1.05 ft of 2.66 ft.
DGAC for an increase in the profile
grade of 0.30 ft. This is 0.25 ft lower in For the estimated 1.25 ft depth, the Gf is
profile grade than the basic overlay 2.18 (HDM, Table 608.4).
design method provided. This would be
an acceptable solution except the GE/Gf = (2.66 ft)/2.18 = 1.22 ft of
problem was to match the existing grade. DGAC. Round to 1.20 ft.
Therefore, find to what depth the milling This is less than the 1.25-ft thickness
has to go to have no increase in profile that was estimated; the depth of the AB
grade. Below the pavement the Gf for to be removed was too much. Therefore,
the existing 0.50 ft of AB material is 1.1. reduce the estimate for the milled depth
The additional GE to be replaced is 1.1 of the AB below the pavement. Try 0.45
times the thickness of the AB layer ft into the AB, for a total thickness of
milled. This will be added to the GE at 1.20 ft (0.75-ft pavement and 0.45 ft
the analytical depth (at the surface in this base).
example) and the GE at the bottom of
GE = (0.45 ft)(1.1) = 0.50 ft. This is
the pavement; then the total is divided by
added to the GE’s at the analytical depth
the Gf of the new DGAC.
and bottom of the pavement, then
Instead of trying each 0.05-ft of milling, divided by the Gf of the 1.20 ft of DGAC
estimate to what depth the milling might obtained from Table 608.4 of the HDM
have to go. A quick calculation of the Gf (Gf = 2.15 ):
ratio times the increase in grade, when
GE/Gf = (1.06 ft + 1.05 ft + 0.50 ft)/2.15
milling stopped at the bottom of the
= 1.21 ft
4-18
______________________________________________________________________________________
Round to 1.20 ft. (This matches the GE/Gf = (2.02 ft)/(2.02) = 1.00 ft.
thickness for which the Gf was used).
The R-value design method determined
Discussion 4-4: Since this is quite deep that the existing structural section should
for the milling analysis the R&R method be removed to a depth of 1.00 ft and
may not be reliable*, check the R-value replaced with new DGAC. The Remove
design to see if it is close to the 1.20-ft and Replace design method produced a
thickness. Only 0.05 ft of AB remains thickness of 1.20 ft of new material.
above the aggregate subbase (AS), Engineering judgment is needed as to
therefore use the R-value of the AS with which depth to use. In this case the
the TI10 of 12. (The R-value is 50 for deflection measurements gives the more
Class 1 and 2, and 40 for Class 3 as per conservative answer and the engineer
HDM, Table 608.4). Assume an R- working on the project may have other
value of 50. The equation to determine data to support the use of the R&R
the GE using the R-value is as follows: method.
GE required=(0.0032)(TI)(100–R-value)
Recommendation 4-4: Mill 0.75 ft (225
GE = (0.0032)(12)(100-50) = 1.92 mm) of the existing pavement and 0.45 ft
(135 mm) of the AB material. Then
For a full depth design, add a safety replace those layers with 1.20 ft (360
factor to the GE of 0.10 ft to allow for mm) of DGAC. This will maintain the
construction tolerances as per the HDM. profile grade.
The GE required is then 2.02 ft.
Since we expect to be close to the same 4 – 70 Asphalt Concrete Overlay

depth determined by the deflection Placed on a Cushion Course
method (a good place to start), use a Gf
of 2.15 for the determined 1.20-ft of AC. In this option, an aggregate base (AB)
(Table 608.4 of the HDM). layer (cushion course) is placed prior to
placing the DGAC pavement. It is used
GE/Gf = (2.02 ft)/(2.15) = 0.94 ft.
Round to 0.95 ft.
• to raise the profile grade above a
This is less than the estimated depth of flooded area; or
1.2 ft. The Gf needs to be lower to
• when sections of newly constructed
increase the depth and balance the
added-on lanes, etc., produce grade
equation. Try a Gf of 2.02 for a 1.00-ft
changes for existing roadways; or
thickness.
• when the basic overlay design
*
produces a larger than desired dense
The analysis is based on deflections measured
graded asphalt concrete (DGAC)
on material in the structural layers as well as
several feet of original ground or fill. The overlay thickness (too costly). As
deeper these layers are disturbed or removed the this design method uses two
more the analysis is based on material that no procedures it can also be used to
longer exists and the analysis becomes less smooth a rough pavement.
reliable. Engineering judgment needs to be
applied.
4-19
______________________________________________________________________________________
As a review, the basic overlay design placed less than 0.35 ft (105 mm) thick
method is based on reducing the 80th and the DGAC surface should never be
percentile deflection (D80) at the surface placed less than 0.20 ft (60 mm) thick on
back to a tolerable level (TDS). the AB.
Knowing the TI, 80th percentile
deflection, and the existing AC
pavement thickness, the gravel Example 4-5: Determine the AC and
equivalence (GE) can be determined. AB thicknesses for a Cushion Course
Using a gravel factor ( Gf ) of 1.9, the design.
thickness of the new AC overlay can be
calculated. Ten-Year 80th Percentile Existing Structural
TI Deflection Section
Please note that when determining the 8.0 0.056 inch 0.55 foot AC
0.50 foot AB
mean and standard deviation of a test
0.83 foot AS
section, do not omit the individual
measurements on isolated failed areas,
since patching failed areas will not be Solution 4-5:
recommended when designing an asphalt
concrete overlay placed on a cushion Recommendations to be considered:
course.
Reflective cracking and ride quality are
For this option, the design is based on inherently provided for in this type of
the same principle as the basic overlay design.
with two exceptions:
• the GE required, much like new
construction, is obtained with Since this design is much like new
combinations of AB and AC construction design, the thickness of the
pavement to reduce the D80 for the existing AC pavement does not enter
new AC pavement, and into the calculations for the aggregate
• the Gf varies with the TI and base and new AC thicknesses. To find
thickness, again like new the minimum DGAC thickness required
construction.* over the AB, use the standard design
equation from the HDM:
The DGAC gravel factor (Gf )
commensurate with the TI and new AC GE = (0.0032)(TI)(100-R)
thickness found in Table 608.4 of the
HDM is used. However, no safety factor Gf for AB is 1.1. The R-value for AB is
of additional thickness for new 78. The GE required over the AB is:
construction as described in the HDM
for the R-value design is to be applied. GE = (0.0032)(8)(100-78) = 0.56 ft.
As in new construction of highway
pavement, an AB layer should never be AC = GE/Gf. Use the Gf obtained from
Table 608.4 of the HDM (Estimate what
*
For an AC thickness greater than 0.50 ft (150 the thickness will be and use that Gf ; or
mm), the Gf increases as the thickness increases; as in this example, start with a Gf of
see HDM Index 608.4 (8).
4-20
______________________________________________________________________________________
2.01; this Gf is good for all values of AC Subtract the GE of the actual DGAC
thickness up to 0.50 ft and a TI of 8.0). thickness from the total GE required to
Therefore, this is an iterative calculation obtain the GE of the AB:
process to get the solution. Round the
thickness to the nearest 0.05 ft. GE of AB = 1.10 ft – 0.60 ft = 0.50 ft.
AC = GE/Gf = 0.56 ft/2.01 = 0.28 ft. Finally, divide by the Gf of the AB and
Round to 0.30 ft. round to the nearest 0.05 ft:
Actual GE provided by the DGAC = AB = GE/Gf = 0.50 ft/1.1 = 0.45 ft.

(0.30 ft)(2.01) = 0.60 ft. Use 0.45 ft of AB.
Recommendation 4-5: Use 0.30 ft (90

Using Table 1, the TDS of the new mm) of DGAC over 0.45 ft (135 mm) of
DGAC thickness (0.30-ft) with a TI of AB
8.0 is 0.022 inch.
Calculate the percent reduction in Example 4-6: What would be the AB

deflection required at the surface (PRD) thickness if the DGAC thickness for the
of the existing pavement (D80 = 0.056 previous example were increased to 0.55
inch) to reduce the TDS for the new ft?
pavement to 0.022 inch.
The Gf varies for AC thicknesses greater
AverageD80 − TDS than 0.50 ft. From HDM Table 608.4,
PRD = (100) for a TI of 8.0 and 0.55 ft of AC, the
AverageD80 GE is 1.12 ft.
Tolerable deflection level of the new

PRD = [(0.056 inch – 0.022 inch)/0.056 pavement from Table 1, is 0.017 inch,
inch](100) = 60.7%. therefore
The next step is to obtain the GE PRD = [(0.056 inch – 0.017 inch)/0.056
required (combination of AB and AC) to
reduce the deflection measured on the inch ] (100) = 69.6 %.
existing surface (0.056 inch) to the
tolerable deflection level of the new AC Using Table 2, Column B, determine the
thickness (0.022 inch). total increase in GE required to reduce
D80 to the TDS for the new pavement:
Using Table 2, Column B, determine the GE = 1.41 ft.
total increase in GE required to reduce
D80 to the TDS for the new pavement Subtract the GE of the actual DGAC
using a PRD of 60.7%. thickness (1.12 ft ) from the total GE
required to get the GE of the AB:
GE (Total required)= 1.10 ft.
GE of AB = 1.41 ft – 1.12 ft = 0.29 ft.
4-21
______________________________________________________________________________________
Finally, divide the GE of AB by its Gf thickness of the DGAC over the ATPB
and round to the nearest 0.05-ft to is based on the equation below. The GE
calculate the AB thickness required: of the AC is 0.4 of the total GE required
over a 50 R-value material [see HDM
GE/Gf = 0.29 ft/1.1 = 0.26 ft. Round to 608.4 (4) (b)]. The minimum thickness
0.25 ft. of DGAC cover over the ATPB should
never be less than 0.20 ft (60 mm).
Use the minimum thickness, 0.35 ft for
AB.
GE over ATPB = [(0.4)(GE required
Recommendation 4-6: Use 0.55 ft (165 over a 50 R-value material)]
mm) of DGAC over 0.35 ft ( 105 mm) of
AB
GE = [(0.4)(0.0032)(TI)(100-R)]
4 – 80 Cushion Course Design with Example 4-7: Use the same data from
Drainage Layer the example problem solved in the
“Asphalt Concrete Overlay Placed on A
In this option, an AB layer (cushion Cushion Course” design, Section 4-70.
course) is placed prior to placing a Determine the AC, ATPB and AB
drainage layer and DGAC pavement. It thicknesses for a Cushion Course design
is similar in design to an “Asphalt with drainage layer.
Concrete Overlay Placed on a Cushion
Course” described in Section 4-70. The Ten-Year 80th Percentile Existing Structural
Gravel Equivalence (GE) for the added TI Deflection Section
layer of the Asphalt Treated Permeable 8.0 0.056 inch 0.55 foot AC
Base (ATPB) is subtracted from the total 0.50 foot AB
GE required. [Note that a drainage layer 0.83 foot AS
requires positive outflow and is
discussed in Highway Design Manual
(HDM), Chapter 600, Topic 606]. The Solution 4-7:
thickness of the ATPB is 0.25 ft (75mm)
unless a unique combination of Recommendations to be considered:
conditions exists. See HDM, Section
606.2. Reflective cracking and ride quality are
inherently provided for in this type of
design.
The Gf for ATPB is 1.4 as obtained from
the HDM, Table 608.4. The GE that the Structural Adequacy:
0.25-ft (75-m) ATPB layer contributes to
the total required thickness is: Find the minimum DGAC thickness
over the ATPB:
GE = (Gf )(AB thickness) = (1.4)(0.25 ft)
GE = 0.35 ft.
The GE over the ATPB is
Since an ATPB drainage layer has an [(0.4)(0.0032)(8)(100-50)] = 0.51 ft.
indeterminate R-value, the minimum
4-22
______________________________________________________________________________________
From the HDM, Table 608.4, the Gf for GE of AB = (0.98 ft)–(0.50 ft) – (0.35 ft)
any thickness of DGAC 0.50 ft or less is GE = 0.13 ft.
2.01. The minimum thickness of cover
for the ATPB is: AB Thickness = GE/Gf = 0.13 ft/1.1
GE/Gf = (0.51 ft)/(2.01) = 0.25 ft. AB = 0.11 ft. Round to 0.10 ft.
Use 0.25 ft.
Use the minimum thickness, 0.35 ft for
Calculate the actual GE provided by the AB.
0.25-ft of DGAC:
Recommendation 4-7 Use 0.25 ft (75
mm ) of DGAC, over 0.25 ft (75 mm ) of
GE = (2.01)(0.25 ft) = 0.50 ft.
ATPB, over 0.35 ft (105 mm ) of AB.
Use the thickness of the new AC
pavement and the design Traffic Index
4 – 90 Asphalt Concrete Overlay with
(TI) in Table 1 to determine that the
Drainage Layer
Tolerable Deflection at the Surface
(TDS) is 0.024 inch.
Determination and discussion of the
need for a drainage layer can be found in
Calculate the percent reduction in
the California Highway Design Manual
deflection required at the surface (PRD)
(HDM), in Chapter 600, Topic 606.
of the existing pavement (D80 = 0.056
Placement and design considerations
inch), to reduce the TDS for the new
such as a positive outflow requirement
pavement to 0.024 inch:
for a drainage layer are also found in the
HDM. This strategy can also be used to
AverageD80 − TDS
PRD = (100) smooth rough pavement as well as
AverageD80 provide the needed drainage since it
utilizes multiple layers.
PRD = [(0.056 inch – 0.024 inch)/0.056 The AC overlay thickness portion of this
inch]100 = 57.1 % strategy is determined using the design
method for a basic overlay, with the
Utilizing the calculated PRD value, go to Gravel Equivalence (GE) of the Asphalt
Table 2, Column B to determine the Treated Permeable Base (ATPB) layer
increase in GE required to reduce the subtracted from the total GE required.
D80 to the TDS for the new pavement: The thickness of the ATPB is 0.25 ft (75
mm) unless unique combinations of
GE (Total Required) = 0.98 ft. conditions were to exist. [See Highway
Design Manual (HDM), Chapter 600,
Subtract the GE of the actual DGAC
Topic 606]. The standard layer of 0.25
thickness (0.50 ft) and the GE of the
ft (75 mm) will generally provide greater
ATPB (0.35 ft) from the total GE
drainage capacity than is needed under
required to get the GE of the AB.
AC pavements. Therefore, the standard
GE (Total Required) = (GE of DGAC) + thickness generally provides sufficient
(GE of ATPB) + (GE of AB) drainage and provides an allowance to
compensate for construction tolerances.
4-23
______________________________________________________________________________________
Calculate the GE that the ATPB (Gf is Step 2:

1.4) contributes to the total required Compare average D80 to TDS.
thickness: 0.030 > 0.012
GE = (1.4)(0.25 ft) = 0.35 ft. Stem 3:

Calculate Percent Reduction in
Since an ATPB drainage layer has an Deflection required.
indeterminate R-value, the minimum
thickness of the DGAC over the ATPB  0.030 − 0.012 
is based on the equation below. The GE  (100) = 60%
 0.030 
of the AC is 0.4 of the total GE required
over a 50 R-value material [HDM 608.4
Step 4:
(4) (b)]. The minimum thickness of
Determine Gravel Equivalence
DGAC over the ATPB should never be
(GE) required for deflection
less than 0.20 ft (60 mm).
reduction.
Use Table 2; Column A
GE over ATPB = [(0.4)(GE required
GE = 0.85 ft
over a 50 R-value material)].
Step 5:
GE = [(0.4)(0.0032)(TI)(100-R)]
Find the minimum DGAC
thickness over the ATPB:
Example 4-8: Determine the AC and

GE over ATPB drainage layer is =
ATPB thicknesses for an existing AC
(0.4)(0.0032)(10)(100 – 50) = 0.64 ft.
pavement.
The DGAC thickness using a Gf = 1.9 is:
TI Deflection Section
AC = GE/Gf = 0.64 ft/1.9 = 0.34 ft.
10.0 0.030 inch 0.55 foot AC
0.50 foot AB Round to 0.35 ft.
1.00 foot AS
Step 6:
Find the DGAC thickness
Calculations 4-8: required to reduce the 80th
percentile deflection down to the
Check for overlay thickness required tolerable level. (Use the standard
for structural adequacy. ATPB layer thickness of 0.25 ft.)
Step 1: The GE that the 0.25-ft ATPB

Obtain tolerable deflection at the layer provides is:
surface (TDS). GE = (ATPB thickness)(Gf )
Use Table 1: GE = (0.25)(1.4) = 0.35 ft
AC = 0.55 ft and TI = 10.0
TDS = 0.012 inch GE of DGAC = Total GE
required - GE of ATPB
GE = 0.85 ft – 0.35 ft = 0.50 ft
4-24
______________________________________________________________________________________
Thickness of DGAC = GE/Gf Therefore, structural adequacy governs

DGAC = 0.50 ft/1.9 = 0.26 ft. the overlay design thickness.
Round to 0.25 ft.
Recommendation 4-8: Place 0.35 ft
This is less than the minimum (105 mm ) of DGAC over 0.25 ft (75
DGAC thickness over the ATPB mm) of ATPB.
layer.
Use 0.35 ft DGAC over 0.25 ft ATPB

for structural adequacy.
Check overlay thickness required for

reflective crack retardation.
To retard reflective cracks entering the

new overlay from the pavement below
choose a thickness for the new overlay at
least one-half the thickness of the
existing AC pavement being overlaid
(up to a maximum of 0.35 ft (105 mm)
for an underlying aggregate base).
Determine half of the existing pavement

thickness:
0.55
overlay = = 0.275 Round
2
to 0.30 ft.
Check overlay thickness required for

smoothness.
The ride quality is improved by adding a

minimum 0.25-ft DGAC overlay placed
in two layers.
Discussion 4-8:
• Reflective cracking requirement is
less than the 0.35-ft DGAC thickness
plus the 0.25-ft layer of ATPB.
• The ride quality is going to be
improved due to the two layers being
placed.
4-25
______________________________________________________________________________________
CHAPTER 5 window of time to schedule deflections

throughout the state. Deflections
measured in the late summer or early fall
APPENDIX in the valley and desert areas, may be
influenced primarily by the temperature
and little by moisture content.
5 – 10 Guidelines for Involving
Moisture and Temperature in Flexible At the present time, Caltrans provides no
Pavement Rehabilitation correction factor for temperature or
moisture content. Since higher
Moisture and temperature affect the pavement temperatures produce higher
strength of the structural section and is deflections, using the actual measured
reflected in the measured deflections. deflection when the average pavement
Pavement deflections increase with an temperature is 70º F (21º C) or more will
increase in the amount of moisture in the somewhat compensate for the lower
underlying materials and an increase in moisture content.
the temperature of the pavement at the
time of testing. Deflections should not be measured
when the pavement surface temperature
A saturated structural section and is 45º F (7º C) or lower. The pavement
subgrade along with a hot summer day temperature above which deflection
would be the extreme condition; the measurements should not be made (the
structural section would be in its weakest maximum pavement temperature at the
condition and produce the highest time of testing) will vary depending on
deflection. Fortunately, this the weight of the deflection apparatus
environment is not the norm in being used. The California
California. The hot season is normally Deflectometer with the Benkelman
the dry time of the year. The most Beam, and Falling Weight
favorable time to measure deflections Deflectometer, due to their higher
(designing for the worst case) is in the weight, should not be used to measure
spring of the year; the moisture content deflections when the pavement surface
of the basement soils will be at or near temperature is 130º F (54º C) or higher.
their highest values and will affect the
deflections more than the moderate The lighter weight of the Dynaflect can
temperature. be used at any pavement temperature
above 45o F (7o C).
Presently, the magnitude of highways
needing rehabilitation makes deflection If other engineers or agencies elect to
measurements a year-round endeavor. use this Caltrans manual, the decision
Judgment is required when considering and the method to correct for moisture
the seasonal variation of temperature, content and/or temperature is left to their
moisture content, and test date for areas discretion.
throughout the state. With the large
variation of elevation in California,
“spring” comes at different times of the
year. Fortunately, this allows a large
5-1
______________________________________________________________________________________
5 – 20 Identifying and Recording 3) Longitudinal and Transverse

Distress Cracking (Photos 11 – 12):
Examples of cracks associated with These types of cracks are primarily

asphalt concrete pavement and the caused by shrinkage of the pavement
reason for the cracks are discussed surface due to low temperature or
below. This may aid the engineer in the asphalt hardening, or the result of
design process. reflective cracks from the underlying
pavement or base. If the roadway in
1) Alligator Cracking (Photos 7–8): Photos 11 and 12 were structurally
adequate with good riding qualities,
Alligator cracking in the wheel path is a rehabilitation may not be warranted.
load-associated, fatigue type of failure Surface cracks should be sealed or a seal
for asphalt concrete. At these locations, coat placed to prevent water from
the evaluated pavement deflections will damaging the structural section.
almost always exceed the tolerable
values indicating that rehabilitation is 4) Shrinkage and Thermal Cracking
needed to restore structural adequacy. (Photos 13 – 14):
Water should be prevented from entering Shrinkage and thermal cracking are not
the structural section in this area load-associated type failures; but traffic
especially, due to the many cracks in a loads can increase the severity of the
small area that will develop into a cracks. Age hardening, overheated
localized failure. As water enters the mixes, insufficient asphalt content, and
structural section through the surface normal thermal conditions are some of
cracks, pumping of fine material from the chief causes of shrinkage and
the roadbed and rutting often follow. thermal cracking.
Sealing the surface cracks as soon as
they first appear will decrease the rate of One of the prime objectives in moderate
deterioration of the structural section. to high rainfall areas is to seal surface
cracks and maintain the seal to prevent
2) Longitudinal Cracking in the water from entering the structural
Wheel Path (Photos 9 – 10): section and causing accelerated roadbed
deterioration. A seal coat can be an
A longitudinal crack in the wheel path is effective treatment in slowing the
considered a load-associated crack. The deterioration due to moisture intrusion.
cracking starts at the bottom of the In areas of low rainfall, structural section
asphalt concrete pavement where tensile deterioration due to moisture entering
stress and strain is highest under the the roadbed may not be a major problem.
wheel load. The cracks propagate to the It is reasonable to delay a ten-year
surface initially as one or more rehabilitation project, or at the most just
disconnected, parallel cracks. After place a seal coat, where traffic loads are
repeated traffic loading the cracks light; rainfall is low; pavement ride
connect, forming many sided, sharp- quality is acceptable; and pavement
angled pieces that develop a pattern deflections indicate good structural
resembling chicken wire or the skin of adequacy. A seal coat can prolong the
an alligator. service life for several years without any
5-2
______________________________________________________________________________________
corrective treatment for such a project. 6) Settlement cracking:

However, a five-year design for the
Capital Preventative Maintenance These types of cracks are generally
Program should not be delayed. nearly longitudinal or crescent-shaped
and are not load-associated type failures;
5) Severe Block Cracking (See but traffic loads can increase the severity
Photo 15): of the cracks. These are due to localized
vertical displacement of the pavement
Block cracking is generally not load- structural section due to slippage of a fill
associated and usually divides the or consolidation of the underlying
pavement into approximately equal size foundation material. One of the prime
polygons or rectangular pieces. It is objectives in moderate to high rainfall
mainly caused by hardening and/or areas is to seal these cracks and maintain
shrinkage of the asphalt and daily the seal to prevent water from entering
temperature cycling. However, severe the structural section and accelerating
block cracking, where the size of the the displacement.
polygon is approximately one or two
feet, is usually the result of a structural 7) Localized Failures (Photo 16):
failure of the pavement when the asphalt
concrete is placed over treated bases Assuming the fatigue failure shown in
such as cement treated base (CTB), lime Photo 16 is not typical of the entire
treated base (LTB), and lean concrete project and is obviously an isolated
base (LCB). It can also occur when an problem, it would be recommended that
asphalt concrete (AC) overlay has been this localized failure be replaced. Once
placed over old portland cement replaced, the rehabilitation of the entire
concrete (PCC) pavement. If the area is roadway can be based on the deflection
localized, the pavement and base should levels and conditions of the remaining
be repaired. If the area is extensive, the pavement. If a thin overlay were to be
rehabilitation design should be sufficient placed over the section of roadway in
to remedy this type of failure. Block Photo 16 without performing repairs, the
cracks are often greater than ¼ inch (5 surface cracks would probably recur in
mm) wide. Pavement deflection analysis the new overlay in less than a year.
on treated bases, which generally
produce low deflections, may not always
provide an adequate overlay thickness
designed for structural adequacy to Cracks should be recorded by name
minimize reflective cracking. width, and extent (using percentages)
Experience has shown that a minimum during the field survey.
0.35-ft (105-mm) AC overlay is required
when severe block cracking exists in the Record whether crack widths are
AC over treated bases or AC over PCC. hairline, ±1/8 inch (3 mm), ±1/4 inch (5
mm), or greater than ½ inch (10 mm).
Record the extent of cracking as follows

(showing the approximate percentages,
using continuous in both wheel paths as
being 100%):
5-3
______________________________________________________________________________________
none or minimal – (0% to 5%); or from the pavement cores where the
isolated – (5% to 10%); layers separate easily. The cause may be
occasional – (10% to 15%); insufficient tack coat at construction.
intermittent – (15% to 50%); Record the number and locations. To
nearly continuous – (50% to 85%); repair, mill deep enough to remove the
continuous -- (85% to 100%). delaminating layers.
Also, the field survey should describe

other distress such as the following:
Patches. Asphalt concrete can been
Bleeding. Excess asphalt appears on the added to distressed pavement in several
surface of the pavement, usually in the ways. A patch can be applied to the
wheel paths. This should be kept from surface as an overlay or placed within
migrating up through the new overlay by the pavement after the distress had been
milling to a satisfactory depth to remove removed. Record the location of the
the saturated AC layer. patches, whether they are in the wheel
path, half lane, or the entire lane; the
Minor – Surface looks slightly damp. type of patches such as pothole, overlay,
Major – Surface appears to be only inlaid, or grader patches; and the size of
asphalt with little to no aggregate patch such as spot (hand placed), short
showing in the surface mix. [up to 100 ft (30 m)], and long [greater
than 100 ft (30 m) ].
Corrugations. Transverse undulations

appear at regular intervals due to the Potholes. Holes in the pavement
unstable surface course caused by stop- generally started when small parts of an
and-go traffic. Corrugations are often alligator-cracked area are dislodged by
associated with shoving and/or traffic together with excessive water.
delamination. Note the size of the area. Record the depth of the pothole if it is
To repair, mill deep enough to remove possible. Patch the potholes prior to
the corrugated layer. rehabilitation.
Light – Caused some vibration of the Small – Less than 1.0-ft (0.30-m) square.
vehicle, which creates no discomfort. Medium – Between 1.0-ft (0.30-m)
Medium – Causes significant vibration and 3.0-ft (0.91-m) square.
of the vehicle that creates some Large – Greater than 3.0-ft (0.91-m)
discomfort. square.
High – Causes excessive vibration of the
vehicle that creates substantial
discomfort and/or vehicle damage
requiring a reduction in speed. Pumping. The ejection of foundation
material through cracks in the pavement
generally leaves the material as visible
residue on the surface. Record the
Delamination. Debonding of the surface number of occasions or accumulated
course from the underlying AC layer is length of the pumping. Rehab should
evidenced by shallow potholes, shoving,
5-4
______________________________________________________________________________________
include limiting water intrusion into the Rutting. Longitudinal depressions in the
base. wheel path usually caused by an unstable
AC mix or inadequate strength of the
Light – Water pumping is observed but underlying material. Since this could be
no fines (or only a very small amount) progressive, removal of the offending
can be seen on the surface of the material may be necessary. If
pavement. progression has stopped, rutting greater
Medium – Some material can be than ½ inch (25 mm) should be milled
observed. off to form an even surface, or an AC
High – A significant amount of pumped leveling course placed, prior to placing
material exists on the surface near the the AC overlay. Rutting may also be
cracks. caused by surface attrition, the abrasive
wear of the pavement from the action of
tire chains.
Raveling. This is a progressive Light – Mean depths range from ¼ inch
disintegration of the asphalt concrete (6 mm) to ½ inch (13 mm);
surface downward by the dislodgment of Medium – Mean depths range from ½
aggregate particles and binder. This inch (13 mm) to 1 inch (25 mm);
could be due to significant hardening of High – Mean depths are greater than 1
the asphalt binder (weathering) and inch (25 mm).
would occur across the entire pavement.
Or it could occur just in the middle of Shoving (slippage). Localized
the lane where the oil that drips from the displacement or bulging of pavement in
vehicles strips the asphalt from the the direction of loading pressure
aggregate. produced by stopping, starting or turning
movements. The pavement may have
Fine – Fine aggregate and/or asphalt low tensile strength and delamination or
binder has worn away and the surface may have bleeding from too much
texture is moderately rough and pitted; asphalt in the mix. Shoving the
Coarse – Coarse aggregate and asphalt pavement forward often produces
binder has worn away, and the surface corrugations ahead of the shoving and
texture is severely rough and pitted. crescent-shaped cracks behind. Note the
size of the area. No degree of severity is
Record whether the location of the defined. Removal of the offending
raveling is in the drip path, wheel path, material is usually necessary.
or across the entire lane.
5-5
______________________________________________________________________________________
Photo 7 – Alligator Cracking
Photo 8 – Severe alligator cracking
5-6
______________________________________________________________________________________
Photo 9 – Longitudinal cracking in wheel path
Photo 10 – Longitudinal cracking in wheel path with pumping
5-7
______________________________________________________________________________________
Photo 11 – Longitudinal and transverse cracking
Photo 12 – Transverse cracking
5-8
______________________________________________________________________________________
Photo 13 - Shrinkage and thermal cracking
Photo 14 - Shrinkage and thermal cracking
5-9
______________________________________________________________________________________
Photo 15 – Severe block cracking
Photo 16 - Localized failure
5-10
______________________________________________________________________________________
5-30 Abbreviations
AB Aggregate Base
AC Asphalt Concrete
AS Aggregate Subbase
ATPB Asphalt Treated Permeable Base
CRAC Cold Recycled Asphalt Concrete
CTB Cement Treated Base
D80 80th Percentile of the Deflections at the Surface, in inches, for a test section
DGAC Dense Graded Asphalt Concrete
DM The calculated Deflection at the Milled depth in inches
ESAL Equivalent Single 18,000-lb Axle Load
GE Gravel Equivalence
Gf Gravel Factor
HDM Highway Design Manual
HRAC Hot Recycled Asphalt Concrete
IRI International Roughness Index
LCB Lean Concrete Base
OGAC Open Graded Asphalt Concrete
OWP Outside Outer Wheel Path
PCC Portland Cement Concrete
PMS Pavement Management System
PRD Percent Reduction in Deflection Required at the Surface
PRM Percent Reduction in deflection required at the Milled depth
R&R Remove and Replace also known as Mill and Fill
RAC (Type G) Asphalt Rubberized – Asphalt Concrete (Type G)
RAP Reclaimed Asphalt Pavement
SAMI-F Fabric Stress Absorbing Membrane Interlayer
SAMI-R Rubberized Stress Absorbing Membrane Interlayer
SSD&R Office of Structural Section Design and Rehabilitation
TDS Tolerable Deflection at the Surface, in inches
TI Traffic Index
5-11
______________________________________________________________________________________
5-40 Definitions graded mixture of coarse aggregate,

portland cement, and water placed as the
base layer to provide adequate drainage
Alligator Cracking. Interconnected or of the structural section, as well as
interlaced load associated (fatigue) structural support.
cracks in asphalt concrete pavement
forming a series of small polygons that Chip Seal. A high viscosity asphaltic
resemble the typical pattern of an emulsion surface coat, which
alligator’s skin. incorporates rolled in rock screenings
(chips) over an asphalt concrete
Asphalt Treated Permeable Base pavement, as preventive maintenance, to
(ATPB). A highly permeable open- extend the service life.
graded mixture of crushed coarse
aggregate and asphalt binder placed as Cold Recycling. The rehabilitation of
the base layer to assure adequate asphalt concrete pavement in place,
drainage of the structural section, as well without the application of heat, by
as structural support. milling and mixing with new binder
and/or rejuvenating agents.
Base. A layer of selected, processed,
and/or treated aggregate material of Composite Pavement. A pavement
planned thickness and quality placed structure or structural section composed
immediately below the pavement and of an asphalt concrete wearing surface
above the subbase or basement soil to and portland cement concrete (PCC)
support the pavement. slab; an asphalt concrete overlay on a
PCC slab is also referred to as a
Basement Material. The material in composite pavement.
excavation or embankments underlying
the lowest layer of subbase, base, Corrugations. Also known as “wash
pavement surfacing or other specified board,” transverse undulations appear at
layer which is to be placed. regular intervals due to the unstable
surface course. This consists of
Basement Soil. See Basement Material. alternating crests and valleys less that 2
feet apart and usually occurs where
Bleeding. Also known as flushing, vehicles stop and start.
excess asphalt appears on the surface of
the pavement, usually in the wheel paths. Crack Seals. Pourable, or extrudable,
Accumulation with time may reduce materials that are placed in cracks to
skid resistance. deter the entry of water and
incompressible materials, and to retard
Block Cracking. Interconnected cracks, the crack from reflecting up into the
which form a series of large polygons, asphalt concrete overlay.
usually with sharp corners or angles.
Block cracking appears on flexible Cushion Course. The layer, generally an
pavement but is not load associated. aggregate base material, that is placed
over an existing pavement to increase
Cement Treated Permeable Base the profile grade and give additional
(CTPB). A highly permeable open-
5-12
______________________________________________________________________________________
structural support before placing the new cleanouts, designed to drain the
asphalt concrete pavement. structural section of both rigid and
flexible pavements.
Delamination. A separation (debonding)
of two layers of asphalt concrete Embankment. A prism of earth that is
generally due to insufficient paint binder constructed from excavated or borrowed
during construction. It causes the two natural soil and/or rock, extending from
layers to act independently from each original ground to the grading plane, and
other. designed to provide a stable support for
the pavement structural section.
Dense Graded Asphalt Concrete
(DGAC). A uniformly graded asphalt Equivalent Single Axle Loads (ESAL’s).
concrete mixture (aggregate and paving Summation of equivalent 18000-lb (80-
asphalt) containing a small percentage of kN) single axle loads used to convert
voids, used primarily as a surface layer mixed traffic to design traffic for the
to provide the structural strength needed design period.
to distribute loads to underlying layers of
the structural section. Flexible Pavement. A traffic load
carrying system that is made up of one
Design Period. The period of time that or more layers that are designed to
an initially constructed or rehabilitated transmit and distribute that loading to the
pavement structural section is designed underlying roadbed material. The
to perform before reaching its terminal highest quality layer is the surface
serviceability or a condition that requires course, (generally asphalt concrete)
major rehabilitation or reconstruction; which is usually underlain by a lesser
this is also referred to as the quality base, and in turn a subbase. It is
performance period. Because of the called flexible because it can tolerate
many independent variables involved, deflection bending under heavy loads.
the service life before major
maintenance or rehabilitation is required Fog Seal. A combination of mixing-type
may actually be considerably longer or asphaltic emulsion and water which is
shorter. applied to the surface of asphalt concrete
pavement to seal the surface, primarily
Drip Path Ravel. Progressive used for pavement maintenance.
disintegration of the surface between
wheel paths on asphalt concrete Grading Plane. The surface of the
pavement, caused by oil and fuel basement material upon which the
dripping from vehicles. This is most lowest layer of subbase, base, pavement
prevalent adjacent to intersections where surfacing, or other specified layer, is
vehicles slow and stop. placed.
Edge Drain System. A drainage system, Hot Recycling. The use of reclaimed
consisting of a slotted plastic collector asphalt concrete pavement which is
pipe encapsulated in treated permeable combined with virgin aggregates,
material and a filter fabric barrier, with asphalt, and sometimes rejuvenating
unslotted plastic pipe vents, outlets, and agents at a central hot-mix plant and
5-13
______________________________________________________________________________________
placed in the structural section in lieu of Maintenance. The preservation of the

all new materials. entire roadway, including pavement
surface and structural section, shoulders,
Lean Concrete Base. Mixture of roadsides, structures, and such traffic
aggregate, portland cement, water, and control devices as are necessary for its
optional admixtures, primarily used as a safe and efficient utilization.
base for portland cement concrete
pavement. Open Graded Asphalt Concrete
(OGAC). An open graded mixture of
Leveling Course. The layer, generally of aggregate and a relatively high asphalt
AC or other treated or processed content, which provides good skid
material, that is placed over the rough or resistance and a high permeability.
undulating surface of an existing OGAC is designed to accommodate
pavement, structure deck, or other rapid surface drainage and minimize the
surface to improve the surface profile or potential of hydroplaning while at the
ride quality before placement of same time providing an effective seal of
subsequent layers. the underlying asphalt concrete
pavement.
Lime Treatment. The mixing of lime
with native or embankment materials to Outside Wheel Path (OWP). The vehicle
increase the strength (R-value) of the tire path closest to the outside edge of
material which supports the pavement pavement. Deflection measurements are
structural section. usually made in the outside wheel path.
Localized Failure. A pavement that is Overlay. An overlay is a layer, usually

within a definite locality that exhibits asphalt concrete, placed on existing
loose and/or spalling pieces of asphalt asphalt or portland cement concrete
concrete pavement, brought on by pavement to restore ride quality, to
alligator cracking, possibly with rutting increase structural strength (load
and insufficient base support. carrying capacity), and to extend the
service life.
Longitudinal Cracking. Cracks or breaks
in flexible or rigid pavement, which are Patches. Corrections to damaged
approximately parallel to the pavement, pavement by adding asphalt concrete. It
center line. could be applied to the surface or placed
after the distress has been removed.
Low-Volume Road. A roadway generally
subjected to low levels of traffic; in the Pavement. The surface layer of the
AASHTO Design Guide, structural structural section that carries traffic.
design is based on a range of 80 kN Except for special or experimental
ESAL’s from 50 000 to 1 000 000 for surface layers, the pavement is either
flexible and rigid pavements, and from portland cement concrete or asphalt
10 000 to 100 000 for aggregate- concrete. The asphalt concrete layer may
surfaced roads. include up to a 30-mm layer of OGAC.
5-14
______________________________________________________________________________________
Pavement Management System (PMS). be only to the next lift of asphalt

A management system, which was concrete or it may extend into the base.
developed by Caltrans, to assess the
condition of pavement, biennially, on the Prepared Roadbed. In-place soils
entire California State Highway System, compacted or stabilized according to
and to prioritize and program the provisions of applicable specifications.
rehabilitation of pavement consistent
with available funding. Present Serviceability Index (PSI). A
term from the AASHTO Design Guide;
Pavement Performance. The trend of a number derived by formula for
serviceability with load applications. estimating the serviceability rating from
measurements of certain physical
Pavement Rehabilitation. Work features of the pavement. Not used
undertaken to extend the service life of directly by Caltrans for pavement
an existing facility. This includes evaluation but conversion is made in
placement of additional surfacing and/or PMS, for comparison.
other work necessary to return an
existing roadway, including shoulders, to Preventive Maintenance. Typically,
a condition of structural or functional capital outlay work performed to
adequacy, for a minimum period of 10 preserve the existing pavement structural
years. This might include the partial or section utilizing strategies that extend
complete removal and replacement of pavement service life for 5 years (i.e.:
portions of the pavement structural for AC pavements, “thick blanket”
section. overlays; for PCC pavements, grinding,
slab replacement, etc.).
Pavement Reinforcing Fabric (PRF or
SAMI-F). A stress absorbing membrane Prime Coat. (Sometimes called tack
interlayer that is a nonwoven, bonded- coat.) The application of a low viscosity
fiber, engineering grade synthetic fabric. liquid bituminous material to an
It is used by Caltrans in asphalt concrete absorbent surface (preparatory to placing
overlays primarily to minimize surface subsequent structural section layers or
water infiltration and retard reflective PRF) for the purpose of hardening or
cracking through the overlay, from toughening the surface and promoting
cracks or joints in the existing pavement. adhesion between it and the
superimposed constructed layer or PRF
Pavement Structure. See Structural interlayer.
Section
Pumping. The ejection of foundation
Pavement Surfacing. See Surface Course material, either wet or dry, through
cracks resulting from vertical
Pot Holes. Bowl-shaped holes of various movements of the pavement under
sizes in the pavement that generally start traffic. This phenomenon is especially
when small parts of an alligator-cracked pronounced with saturated structural
area are dislodged by traffic together sections.
with excessive moisture. The depth may
5-15
______________________________________________________________________________________
Raveling. Gradual degradation of the Roadbed Material. Also referred to as

pavement surface. Weathering or basement soil or basement material, the
stripping of the asphalt from the material below the grading plane in cuts
aggregates, along with action of the tires, and embankments, extending to such
causes separation of the aggregates and depths as affect the support of the
asphalt. Stripping may be accomplished pavement structure or structural section.
by an excessive amount of water with
the tire action, or by oil and gas dripping Rubberized Asphalt. A mixture of paving
from passing vehicles (drip track asphalt combined with specified
raveling). Raveling in the wheel path percentages of granulated reclaimed
may also be caused by abrasive chain rubber for use as the binder in asphalt
wear. concrete and in stress absorbing
membrane interlayers (SAMI-R) within
Reflective Cracking. Generally occurs on or under asphalt concrete overlays.
pavements that have an asphalt concrete Primary applications where benefits
surface over jointed portland cement appear to be significant are for providing
concrete or a cement treated base. This more resilient and more durable wearing
is mainly caused by movement of the surface for overlays, to retard reflective
PCC or CTB because of thermal and cracking and overlays on pavement
moisture changes. exposed to wear by tire chains.
Rubberized asphalt joint sealant is used
Resurfacing. A supplemental surface to keep out incompressible materials and
layer or replacement layer placed on an retard surface water infiltration.
existing pavement to restore its riding
qualities or to increase its structural Rubberized Asphalt Concrete Type G
(load carrying) strength. (RAC Type G). Also known as Asphalt
Rubber Hot Mix – Gap Graded. A gap
Rigid Pavement. Primarily portland graded mixture of crushed coarse and
cement concrete pavement, which fine aggregate, and of paving asphalt
distributes the superimposed axle loads that are combined with specified
over a relatively wide area of underlying percentages of granulated (crumb)
structural section layers and soil because reclaimed rubber. Generally, the crumb
of its rigidity and high modulus of rubber is blended and partially reacted
elasticity. with asphalt cement prior to mixing with
the aggregate in a hot mix plant.
Roadbed. The roadbed is that area Primary applications, where benefits
between the intersection of the upper appear to be significant, are for
surface of the roadway and the side providing more resilient and more
slopes or curb lines. The roadbed rises in durable wearing surface for overlays, to
elevation as each increment or layer of retard reflective cracking and overlays
subbase, base, surfacing or pavement is on pavement exposed to wear by tire
placed. Where the medians are so wide chains.
as to include areas of undisturbed land, a
divided highway is considered as Rutting. Longitudinal depressions that
including two separate roadbeds. develop in the wheel paths of flexible
pavement under traffic. Unstable asphalt
5-16
______________________________________________________________________________________
concrete pavement or inadequate pavement may have low tensile strength

strength of the underlying foundation and delamination or may have bleeding
most often causes this permanent and from too much asphalt in the mix.
sometimes progressive deformation. Shoving the pavement forward often
Rutting may also occur due to chain or produces corrugations ahead of the
studded tire abrasion or raveling. shoving and crescent-shaped cracks
behind.
R-value. Resistance value of treated or
untreated soil or aggregate as determined Single Axle Load. The total load
by the stabilometer test (California Test transmitted by all wheels whose centers
301). This is a measure of the supporting may be included between two parallel
strength of the basement soil and transverse vertical planes 1.016 m (40
subsequent layers used in the design of inches) apart, extending across the full
pavement structural sections. width of the vehicle.
Seal Coat. A bituminous coating, with or Slurry Seal. A mixture of mixing-type

without aggregate, applied to the surface asphaltic emulsion, fine mineral
of a pavement for the purpose of aggregate and water proportioned, mixed
waterproofing, preserving, or and spread primarily on asphalt concrete
rejuvenating a cracked or raveling pavement for maintenance purposes.
bituminous surface, or to provide
increased skid resistance or resistance to Spalling. Cracking, breaking, or
abrasion by traffic. chipping of the edge of a crack in which
small portions of the pavement are
Serviceability. The ability at time of dislodged. Spalling is caused primarily
observation of a pavement to serve by nonuniform support in conjunction
traffic (autos and trucks) which use the with vertical movement due to wheel
facility. loads or incompressibles confined in the
opening.
Settlement. Localized vertical
displacement of the pavement structural Stress Absorbing Membrane Interlayer
section due to slippage of a fill or (SAMI). An interlayer placed within or at
consolidation of the underlying the bottom of an asphalt concrete
foundation, often resulting in pavement overlay or layer to retard reflective
cracking and a poor ride quality. cracking and prevent water intrusion.
Examples include a rubberized chip seal
Shoulder Backing. A material that is interlayer (SAMI-R) or pavement
placed adjacent to the outside edge of reinforcing fabric (SAMI-F).
the shoulder surfacing to protect the
edge from spalling, and to provide edge Stripping. The loss of the adhesive bond
support. between asphalt cement and aggregate,
most often caused by the presence of
Shoving. Localized displacement or water in asphalt concrete, which may
bulging of pavement in the direction of result in raveling, loss of stability and
loading pressure produced by stopping, load carrying capacity of the asphalt
starting or turning movements. The concrete pavement or treated base.
5-17
______________________________________________________________________________________
Structural Section. The planned, Surface Polish. The loss of the original
engineering-designed layers of specified pavement surface texture due to traffic.
materials (normally consisting of
subbase, base, and pavement surface) Surface Recycling. In-place heating of
placed over the basement soil to support the surface of asphalt concrete pavement
the traffic loads anticipated to be followed by scarification, remixing, and
accumulated and applied during the compaction, generally to a depth of
design period. The structural section is about 20 mm. This is considered to be a
also commonly called the pavement maintenance procedure.
structural section.
Tack Coat (Paint Binder). The
Structural Section Drainage System. A application of bituminous material to an
drainage system used for both asphalt existing surface to provide bond between
and portland cement concrete pavements the superimposed construction and the
consisting of a treated permeable base existing surface.
layer and a collector system which
includes a slotted plastic pipe Tandem Axle Load. The total load
encapsulated in treated permeable transmitted to the pavement by two
material and a filter fabric barrier with consecutive axles whose centers may be
unslotted plastic pipe as vents, outlets included between parallel vertical planes
and cleanouts to rapidly drain the spaced more than 1.016 m (40 inches)
pavement structural section. and not more than 2.438 m (96 inches)
apart, extending across the full width of
Subbase. A layer of aggregate of the vehicle.
designed thickness and specified quality
placed on the basement soils as the Transverse Cracking. Cracks in asphalt
foundation for a base. concrete pavement approximately at
right angles to the centerline most often
Subgrade. That portion of the roadbed created by thermal forces exceeding the
on which pavement surfacing, base, tensile strength of the asphalt concrete.
subbase, or a layer of any other material
is placed. Weathering. Gradual degradation of the
pavement surface. Oxidation and
Surface Attrition (“Abrasion”). hardening of the asphalt cause separation
Abnormal surface abrasion wear of from the aggregates, along with action of
pavement, resulting from either a poor the tires, result in surface raveling.
quality surface or exposure to abnormal
abrasive action (such as tire chains and Wearing Course. See Surface Course.
sanding materials) or both.
Surface Course. The top layer of AC

pavement. It is also sometimes called the
“wearing course”.
5-18
______________________________________________________________________________________
5-50 Bibliography
1. Hveem, F. N., “Pavement Deflections and Fatigue Failures,” Highway Research

Board Bulletin 114, 1955.
2. Zube, E. and Forsyth, R. A., “Flexible Pavement Maintenance Requirements as

Determined By Deflection Measurements,” Proceedings, 45th Annual Meeting of the
Highway Research Board, January 1966.
3. Bushey, Roy W.; Baumeister,K. L.; Matthews, James A.; Sherman, George B.;
“Structural Overlays for Pavement Rehabilitation,” Interim Report, California
Department of Transportation, July 1974.
4. State of California, Department of Transportation, Caltrans Standard Test Methods,

Vol. 2, California Test 356.
5. “Asphalt Concrete Overlay Design Manual,” California Department of

Transportation, January 1979.
6. Mann, Gary W.; Matthews, J. A.; Webster J. T.; “An Evaluation of the Current
California Method To Determine Asphalt Concrete Overlay Thickness,” California
Department of Transportation, June 1980.
7. Hannon, J.B.; Mason, P. E.; Boerger, E.; “Determine Gravel Equivalent Factor For
Cold Recycled Asphalt Pavement,” Final Report of Minor Research Study, California
Department of Transportation, Office of Transportation, August 1988.
8. State of California, Department of Transportation, “Chapter 600, Design of the

Pavement Structural Section,” Highway Design Manual, Fifth Edition, Sacramento,
California.
9. State of California, Department of Transportation, “Standard Specifications, July

1999.”
5-19
______________________________________________________________________________________
CHAPTER 6
TABLES
TABLE 1*
TOLERABLE DEFLECTIONS
( x 0.001 inches )
-------------------------------------------------------------------------------------------------------------
DGAC TraffIc Indexes ( T I ' s )
Depth
( foot ) 5 6 7 8 9 10 11 12 13 14 15 16
--------------------------------------------------------------------------------------------------------------
0.00 66 51 41 34 29 25 22 19 17 15 14 13
0.05 61 47 38 31 27 23 20 18 16 14 13 12
0.10 57 44 35 29 25 21 19 16 15 13 12 11
0.15 53 41 33 27 23 20 17 15 14 12 11 10
0.20 49 38 31 25 21 18 16 14 13 12 10 10
0.25 46 35 28 24 20 17 15 13 12 11 10 9
0.30 43 33 27 22 19 16 14 12 11 10 9 8
0.35 40 31 25 20 17 15 13 12 10 9 8 8
0.40 37 29 23 19 16 14 12 11 10 9 8 7
0.45 35 27 21 18 15 13 11 10 9 8 7 7
0.50 ** 32 25 20 17 14 12 11 9 8 8 7 6
CTB *** 27 21 17 14 12 10 9 8 7 6 6 5
--------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------
5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5 13.5 14.5 15.5 16.5
--------------------------------------------------------------------------------------------------------------
0.00 58 45 37 31 27 23 20 18 16 15 13 12
0.05 53 42 34 29 25 21 19 17 15 14 12 11
0.10 50 39 32 27 23 20 18 16 14 13 11 11
0.15 46 36 30 25 21 19 16 14 13 12 11 10
0.20 43 34 28 23 20 17 15 14 12 11 10 9
0.25 40 32 26 22 19 16 14 13 11 10 9 8
0.30 37 29 24 20 17 15 13 12 11 9 9 8
0.35 35 27 22 19 16 14 12 11 10 9 8 7
0.40 32 26 21 18 15 13 11 10 9 8 8 7
0.45 30 24 20 16 14 12 11 9 9 8 7 6
0.50 ** 28 22 18 15 13 11 10 9 8 7 7 6
CTB *** 24 19 15 13 11 10 8 7 7 6 5 5
--------------------------------------------------------------------------------------------------------------
Based on the following equation: Tol. Defl. = 10 [ A – (1.41 )( Log TI ) ] where the intercept, A, for each depth is
as follows:
AC Depth (foot) / A-Intercept:
• 0.00 / 2.804 0.15 / 2.708 0.30 / 2.615 0.45 / 2.524

• 0.05 / 2.771 0.20 / 2.677 0.35 / 2.584 0.50 / 2.494
• 0.10 / 2.739 0.25 / 2.646 0.40 / 2.554 CTB / 2.418
• * Same as the Tolerable Deflection Chart in the 1979 Asphalt Concrete Overlay Design Manual. (5)
** For an AC thickness greater than 0.50 ft. use the 0.50 ft depth.
*** Use the CTB line to represent treated base materials that are equal to or greater than 0.35 ft (105
mm) thick or if the base is a PCC pavement, regardless of the thickness of AC cover. If the underlying
treated base thickness is less than 0.35 ft (105 mm), consider it an untreated base.
6-1
______________________________________________________________________________________
TABLE 2
GRAVEL EQUIVALENCE NEEDED FOR DEFLECTION REDUCTION
------------------------------------------------------------------------------------------------------------------------------------
COLUMN A COLUMN B * COLUMN A COLUMN B *
Percent GE in Feet GE in Feet Percent GE in Feet GE in Feet
Reduction For AC Overlay For AC Over Reduction For AC Overlay For AC Over
In Deflection Design cushion course In Deflection Design cushion
----------------- --------------------- -------------------- ----------------- -------------------- --------------------
5 0.02 0.02 46 0.55 0.62
6 0.02 0.02 47 0.57 0.65
7 0.02 0.02 48 0.59 0.68
8 0.02 0.02 49 0.61 0.71
9 0.03 0.03 50 0.63 0.74
10 0.03 0.03 51 0.66 0.77
11 0.04 0.04 52 0.68 0.81
12 0.05 0.05 53 0.70 0.84
13 0.05 0.05 54 0.72 0.88
14 0.06 0.06 55 0.74 0.91
15 0.07 0.07 56 0.76 0.94
16 0.08 0.08 57 0.79 0.98
17 0.09 0.09 58 0.81 1.01
18 0.09 0.09 59 0.83 1.05
19 0.10 0.10 60 0.85 1.08
20 0.11 0.11 61 0.87 1.11
21 0.12 0.12 62 0.89 1.15
22 0.14 0.14 63 0.91 1.18
23 0.15 0.15 64 0.94 1.22
24 0.16 0.16 65 0.96 1.25
25 0.18 0.18 66 0.98 1.28
26 0.19 0.19 67 1.00 1.32
27 0.20 0.20 68 1.02 1.35
28 0.21 0.21 69 1.04 1.39
29 0.23 0.23 70 1.06 1.42
30 0.24 0.24 71 1.09 1.45
31 0.26 0.26 72 1.11 1.49
32 0.28 0.28 73 1.13 1.52
33 0.29 0.30 74 1.15 1.56
34 0.31 0.32 75 1.17 1.59
35 0.33 0.33 76 1.19 1.62
36 0.35 0.35 77 1.22 1.66
37 0.37 0.37 78 1.24 1.69
38 0.38 0.39 79 1.26 1.73
39 0.40 0.41 80 1.28 1.76
40 0.42 0.43 81 1.30 1.79
41 0.44 0.46 82 1.32 1.83
42 0.46 0.49 83 1.34 1.86
43 0.48 0.52 84 1.37 1.90
44 0.51 0.55 85 1.39 1.93
45 0.53 0.58 86 1.41 1.96
* This column is derived from modifications to Figure 18 in the 1978 California Test 356 that established a
GE for AC over a cushion course design.
6-2
______________________________________________________________________________________
Data for Table 2*
Equations For Column A Equations For Column B

y < 10 y < 10
x = y / 333.33333 x = y / 333.33333
10 ≤ y < 20 10 ≤ y < 20
x = (y-6.25) / 125.00000 x = (y-6.25) / 125.00000
20 ≤ y < 30 20 ≤ y < 30
x = (y-11.53846) / 76.92308 x = (y-11.53846) / 76.92308
30 ≤ y < 40 30 ≤ y < 40
x = (y-16.66667) / 55.55556 x = (y-17.36843) / 52.63158
40 ≤ y 40 ≤ y < 50
x = (y-20.46512) / 46.51163 x = (y-26.12904) / 32.25807
50 ≤ y
x = (y-28.2353) / 29.41177
x in feet
y in percent
*This data was derived from the curve in the 1979 Asphalt Concrete Overlay Design
Manual.
6-3
______________________________________________________________________________________
Table 3
Structural Equivalencies for RAC Type G
Thickness in feet
DGAC RAC Type G RAC Type G on SAMI-R
0.15 0.10 -
0.20 0.10 -
0.25 0.15 0.10
0.30 0.15 0.10
0.35 0.20 0.15
0.40 0.20 0.15
0.45 0.15 (1) 0.20
(2)
0.50 0.15 0.20
0.55 0.20 (1) 0.15 (3) (5)
0.60 0.20 (2) 0.15 (4) (5)
Notes:
(1) Place 0.15 ft (45 mm) of new DGAC then place the RAC Type G. (See Note 5.)
(2) Place 0.20 ft (60 mm) of new DGAC then place the RAC Type G. (See Note 5.)
(3) Place 0.15 ft (45 mm) of new DGAC; a SAMI-R; then 0.15 ft (45 mm) of RAC Type G.
(4) Place 0.20 ft (60 mm) of new DGAC; a SAMI-R; then 0.15 ft (45 mm) of RAC Type G.
(5) If the existing surface is open graded asphalt concrete, it has to be milled off prior to placing the new
DGAC. Therefore, a new calculation should be completed to determine the correct thickness to be placed
after the reduction of the structural section by the milling procedure.
Table 4
Reflective Crack Retardation Equivalencies
Thickness in feet
DGAC RAC Type G RAC Type G on SAMI-R
0.15 0.10 -
0.20 0.10 -
0.25 0.15 -
0.30 0.15 -
(6) (7)
0.35 0.15 or 0.20 0.10 or 0.15 (8)
Notes:
(6) A DGAC thickness of 0.35 ft (105 mm) is usually the maximum thickness recommended by Caltrans
for reflection crack retardation on AC pavements. (See discussions on Page 29.)
(7) Use 0.15 ft (45 mm) only if the crack width is < 1/8 inch (3 mm). Use 0.20 ft (60 mm) if the crack
width is ≥ 1/8 inch (3 mm) or if the underlying material is a CTB, LCB, or PCC.
(8) Use 0.10 ft (30 mm) if the crack width is ≥ 1/8 inch (3 mm) and the underlying base is an untreated
material. Use 0.15 ft (45 mm) if the crack width is ≥ 1/8 inch (3 mm) and the underlying base is a
CTB, LCB, or PCC. Do not use a SAMI-R if the crack width is < 1/8 inch (3 mm).
6-4
______________________________________________________________________________________
Table 5 Layer Thickness

Conversion
Feet mm
0.05 15
0.06 18
0.08 25
0.10 30
0.15 45
0.20 60 *To be uniform statewide for AC structural section
0.25 75 designs, the layer thickness found in the Highway
0.30 90 Design Manual Table 608.4 and shown in this
0.35 105 appendix should be followed whenever possible.
0.40 120
0.45 135 The conversion to metric values used by Caltrans
0.50 150 is based on 0.05 ft equals 15 mm. This is not an
0.55 165 exact calculated or soft conversion, but rather
0.60 180 a hard conversion
0.65 195
0.70 210
0.75 225
0.80 240
0.85 255
0.90 270
0.95 285
1.00 300
1.05 315
1.10 330
1.15 345
1.20 360
1.25 375
1.30 390
1.35 405
1.40 420
1.45 435
1.50 450
1.55 465
1.60 480
1.65 495
1.70 510
1.75 525
1.80 540
1.85 555
1.90 570
1.95 585
2.00 600
2.05 615
2.10 630
2.15 645
2.20 660
2.25 675
2.30 690
2.35 705
2.40 720
6-5
______________________________________________________________________________________
End of Manual
6-6

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STATE OF CALIFORNIA

Revised: June 1, 2001

The information contained in this manual is a result of efforts of many individuals

2 PERFORMING A DEFLECTION STUDY

3 INTRODUCTION TO AC PAVEMENT REHABILITATION DESIGN

4 FLEXIBLE PAVEMENT REHABILITATION DESIGN GUIDE

CHAPTER 1 deflections eventually provided the basis

In 1979, the “Asphalt Concrete Overlay 1 – 20 Foreword

CHAPTER 2 done at least annually. For routine

The Traveling California Deflectometer

The California Deflectometer is

Photo courtesy of Roger Smith

Photo 1 – California Traveling Deflectometer

Photo 2 - Benkelman Beam

Photo 3 - KUAB Falling Weight Deflectometer

Photo 4 – JILS Falling Weight Deflectometer

2 – 20 Establishing Test Sections measured in the OWP, wherever

for pavement deflection measurements. date of placement, and the project’s

Background information is obtained

designer to adjust the rehabilitation to 2 – 60 Converting to Equivalent

2 – 50 Measuring Deflections Individual deflection readings for each

when calculating mean and 80th D80 = x + 0.84 s

The mean deflection level for a test

section is determined by dividing the

x = mean deflection for a test section

n = number of measurements in the

The 80th percentile deflection value

Example 2-1: Determine the mean and D80 = x + 0.84 s

Sum of 21 deflections = 0.725 inch

EXAMPLE OF DEFLECTION MAP

NB Pavement deflections taken at 0.01-mile intervals.

Avg. 80th percentile Avg. 80th percentile

Note: All deflections are in terms of equivalent California Deflectometer values.

Date Tested: 4/21/00

CHAPTER 3 select the corresponding TI for the new

There are three components to be

• Average existing asphalt concrete average existing AC pavement thickness

• Traffic Index (TI). For existing AC pavement over

When the D80 value for deflections of a PRD = Percent Reduction in

Engineering judgment is required when D80 = 80th Percentile of the

A gravel factor (Gf) expresses the

Commonly Used Gf for Rehabilitation is especially applicable when an increase

Aggregate Solution 3-1:

Step 5: minimum thickness of 0.45 ft. (135 mm)

3 - 30 Design Governed by Ride 3 - 40 Choosing the Design

The Pavement Management System The final choice of the recommended

It has been found that during

considerably before adequate Ride Quality:

4 – 10 Basic Overlay Using DGAC n = number of measurements in the

Dynaflect deflection values (Caltrans 4. Determine the Tolerable Deflection at

D80 = 80th percentile of the 5. Calculate the Percent Reduction in

TDS = Tolerable Deflection at the Ten-Year 80th Percentile Existing Structural

overlay = A minimum of 0.25 ft Step 4:

Step 5: • For this overlay example, reflective

4 – 20 Rubberized Asphalt Concrete A Rubberized Stress Absorbing

* Data from field and laboratory studies were

4 – 30 Stress Absorbing Membrane

leveling course of DGAC prior to the

17 policy statement, effective November thicknesses will have slight variations,