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CENG 6302
PAVEMENT ANALYSIS AND DESIGN
CHAPTER 7 OVERVIEW OF RIGID
PAVEMENT DESIGN
Alemgena Alene, PhD, MSc. BSc.
Email: alemgena@yahoo.com

Department of Civil Engineering

Ethiopian Institute of Technology (EiT) – Mekelle
Mekelle University

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

CENG 6302 Pavement Analysis & Design

Course content
Chapter Title
Ch1 Introduction
Ch2 Pavement Performance and Early Design
Ch3 Stresses and Strains in Flexible Pavements
Ch4 Loads on Pavements (ESA)
Ch5 Principle of Probabilistic Design Approaches
Ch6 Design for Rehabilitation and Upgrading
Ch7 Overview of Rigid Pavement Design
Ch8 Overview of Small Element Pavement Design
Ch9 Drainage and Road Embankment Design
Overview

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

7.1. INTRODUCTION
• Rigid pavement
application
• Highways
• Airports
• Streets & local roads
• Parking lots
• Industrial facilities and
• others

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

• Concrete pavements Knowledge of

• Generally higher initial cost Mixture proportioning
than asphalt Design detailing
• But lasts longer (25-40 years) Drainage
and has lower maintenance Construction techniques and
costs Pavement performance
• Design & construction errors
Is essential in addition to
or poorly selected materials theoretical framework of design
have considerably reduced and application procedure
pavement life

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Aspects of concrete pavements

• Economy, service life and • Sustainability
life cycle costs Sustainable development is defined
as “the challenge of meeting human
• Maintenance and needs for natural resources,
industrial products, energy, food,
rehabilitation transportation, shelter, and effective
• Meeting congestion and safety waste management while conserving
and protecting environmental quality
challenges and the natural resource base
• Minimizing road user delays cost essential for future development”
• Short curing time (traffic 6-8 hrs) (ASCE 2006)
• Environmental impacts
“As the world’s non-renewable
• Large quantity of aggregate resources such as fossil
similar to asphalt pavements fuels and roadway aggregates
• Cement production: large decrease in availability, it is important
amounts of energy & release of for all levels of government to begin
CO2 considering paving structures on a
sustainability basis rather than just a
first cost basis”

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Some of the environmental and sustainability benefits of concrete

pavements
• Reductions of 2.4–30 % in energy requirements for pavement
construction and maintenance, with higher savings for more heavily
trafficked highways.

• Reduced heavy vehicle fuel consumption and greenhouse gas

production (particularly CO2) because concrete pavement has less
rolling resistance, therefore requiring lower vehicle power. Fuel
reductions of up to 20 % have been observed.

• Concrete pavements use less granular material or aggregate

throughout the pavement structure because base layers are not
needed. Asphalt pavements may use twice as much. These materials
are growing scarcer, and hauling aggregates represents a significant
fraction of the environmental impact of highway construction.

• Supplementary cementitious materials – fly ash, ground granulated

blast furnace slag, and silica fume – are industrial by-products and
their use in concrete reduces volumes of waste.

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch1 MU-EiT

Types of Concrete Pavements

• Different types of
concrete pavements
have two features in
common:
• Resist traffic loading
through flexure of the
concrete; if reinforcement
is used it is for crack
control and not to carry
load
• Deal with movements due
to thermal effects i.e.
expansion and contraction
using joints, reinforcing
steel or both

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Jointed Plain Concrete Pavements (JPCP)

• Unreinforced concrete slabs 3.5 –
6 m in length with transverse
contraction joints between the
slabs
• Constructed with closely spaced
joints so that cracks should not
form in the slabs
• For JPCP, the pavement
expansions and contractions are
addressed through joints
•

• Dowels or aggregate interlocks

may be used for load transfer
• Aggregate interlock joints are
formed during construction by
sawing 1/4−1/3 of the way through
the pavement to create a plane of
weakness
• A crack then propagates through
the remaining thickness of the
pavement as the concrete
contracts.

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

• The crack has a rough surface Key performance issue of

• The joint can transfer load as long as JPCP:
joints are narrow
• Load transfer is compromised if the • initial pavement smoothness,
joint opens too widely or if the which is a function of
aggregates wear away construction practices
• When the pavement carries heavy
vehicle traffic, particularly at high • adequate pavement thickness to
speeds, aggregate interlock will break
down over time and will not prevent prevent mid-slab cracking
faulting over the life of pavement
Dowels are provided across joint for • limiting the joint spacing, also to
load transfer prevent mid-slab cracking
Dowels are smooth rods, generally
plain or epoxy-coated steel, which are • adequate joint design, detailing,
usually greased or oiled on side to and construction
allow the joint to open and close
without resistance
• JPCP is the most common used type
of concrete pavement because it is
the cheapest to construct

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Jointed Reinforced Concrete Pavements (JRCP)

• Reinforcement in the form of • Steel is placed at the midpoint of the
wire mesh or individual slab thickness i.e. neutral axis
reinforcing bars • It has no effect on the flexural
• Allow the use of longer joint performance and serves only to keep
spacing cracks together
• Was widely used in the past but less
• Reinforcement increases with common today
the increase of in joint • The only advantage over JPCP is
spacing fewer joints
• The light reinforcement is Outweighed by cost of steel and poor
some times termed as performance of the joints and the
temperature steel cracks
• Slab length ranges 7.5 – 9 m
although slab lengths up to 30
m have been used
• With these slab lengths, the
joints must be doweled
• Typical reinforcement range
0.10 – 0.25 % of cross-
section in the longitudinal
direction with less steel in the
transverse

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Continuous Reinforced Concrete Pavement (CRCP)

• Elimination of joints with • Because of the steel
heavy reinforcement (0.4 – reinforcement, CRCP costs
0.8 %) in the longitudinal more than JRCP and thus use
• Steel in the transverse is less frequent
provided as temperature steel • However provides a smoother
• Would decrease the thickness ride and a longer life than any
of pavement required type of pavement
• Transverse cracking at
relatively close interval (0.6 –
2 m)
• The reinforcement holds the
cracks tightly together and
provides aggregate interlock
and shear transfer

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

• Key performance
consideration for CRCP

• initial pavement smoothness

• adequate pavement thickness

to prevent excessive
transverse cracking

• adequate reinforcing steel to

hold cracks together and
prevent punchouts.
Punchouts are a distress
mechanism distinct to CRCP

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Conventional Pavement Joints

• JPCP, JRCP and CRCP make
use of several types of
transverse and longitudinal
joints

• Transverse contraction joints

are used in JPCP and JRCP,
usually with dowels

• Transverse construction joints

are placed, generally at the
location of a planned contraction
joint for JPCP or JRCP

• Transverse expansion or
isolation joints are placed
adjacent to bridges or other
drainage structures

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

• Longitudinal contraction joints • Distresses that may result from

are created where two or more joint failure include
lane widths or shoulders are • faulting,
paved at the same time • pumping,
• spalling,
• In contrast, longitudinal • corner breaks,
construction joints are used • blowups, and
between lanes or shoulders • mid-panel cracking
paved at different times
• Satisfactory joint performance is
The performance of concrete characterized by
pavements depends to a large • Adequate load transfer
extent upon the satisfactory • Proper concrete consolidation
performance of the joints
• Regardless of the joint sealant
 Most jointed concrete pavement material used, periodic resealing
failures can be attributed to will be required to ensure
failures at the joint, as opposed satisfactory joint performance
to inadequate structural capacity

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Transverse contraction joints

• Defined as “ a sawed, formed or • The primary purpose transverse
tooled groove in a concrete slab
that creates a weakened vertical contraction joints is
plane” • To control cracking that results from
• Regulates location of cracking tensile and bending stresses in
caused by dimensional change concrete slab caused by the cement
• It is the most common type of joint hydration process, traffic loadings
in concrete pavements and the environment

• Lightly loaded joints – rely on • The performance of transverse

aggregate interlock across joints contraction joints is related to
• Heavily loaded joints – always three major factors
use load transfer dowels
• Joint spacing
• Load transfer across the joints
• Dowels prevent vertical
movement or faulting between • Joint shape and
slabs, but allow joints to open and • Sealant properties
close to relieve stress buildup due
to temperature and moisture
changes

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8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Longitudinal joints
• Defined as “a joint between two
slabs which allows slab warping
without appreciable separation or
cracking of the slabs …”
• Used to relieve warping stresses
and are generally needed when
slab widths exceed 4.6 m
• Longitudinal joints should • Other joints
coincide with pavement lane lines • Construction joints
when possible to improve
operations • Expansions joints
• Load transfer at longitudinal joints
is achieved through aggregate
interlock
• To aid load transfer, tie bars are
often used across longitudinal
joints
• Tie bars are thinner than dowel
bars

Expansion joint detail

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Concrete pavement structures

• Common thickness of the • Subgrade

concrete top layer is 150 mm • The modulus of elasticity of the
to 450 mm dependent on: concrete top layer >> underlying
• Traffic loading layers
• Climate Bearing capacity of subgrade
has only a small effect on the
• Concrete quality stresses in the concrete layer
• Type of concrete pavement and due to traffic
• Properties of substructure But great effect on the vertical
materials displacement (deflections) of CP
The subgrade is simply
• Considering the great load schematize as a Winkler-
spreading in the concrete top foundation with elastic spring
stiffness k0.
layer, for reasons of strength
base is not (always)
necessary

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8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Evaluation of design
• Yoder and Witczak note:
• Early concrete pavement were
built directly on subgrade
• Regardless of subgrade type
and drainage
• Typical slab thickness were
150 – 175 mm
• With increasing traffic after WW
II, pumping became an
increasingly important
phenomenon
• Thickened edge sections were
common in 1930s & 1940s
• As designs evolved,
pavements were built over
granular subbases to prevent
pumping

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

• Subbase • Similar to subgrade bearing

• Thickness of subbase
capacity of the subbase has
dependent on limited effect on the stresses in
• Designed height level of road
the concrete due to loading
surface
• Frost penetration depth (cold • In design of CP the effect of
climate)
subbase generally is taken into
• Permeability and bearing capacity
of the subgrade account by a certain increase
• Traffic loadings and (depending on the thickness and
• Properties of the subbase material modulus of elasticity) of the
• Unbound granular material
subgrade reaction k0.
with grading meeting filter
criteria to the subgrade
material and base is used

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8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Base Concrete top layer

• Base layer is required • Mechanical properties of
• Not for strength reason, but concrete
• Resistance to erosion under • Concrete qualities are denoted
concrete to ensure a good as c-values where the value
support represents the characteristic
• Reduce deflection of CP (95% probability of exceeding)
cube compressive strength
• Support construction traffic and
equipment (the paver) with an • In the ERA design manual C40
even surface is assumed
• At each side the base has to
be at least 0.5 m wider than
the concrete layer, to give
sufficient support for the
paver
• Can be unbound material or
cement-bound materials

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Reading Assignment II
• Ref. 4 - Chapter 5
Selection of Concrete
Materials [pp. 95-110]
Optimized combined aggregate
grading – shilstone

• Ref. 4 - Chapter 6
Mixture Design and
Proportioning [pp. 111-
128]

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7.2. Stresses and deflections in rigid pavements

Structural Response Models

 Different analysis methods for AC and PCC .

AC PCC Slab

Base
Subgrade
Subgrade

•Layered system behavior. • Slab action

• All layers carry part of load. predominates.
• Slab carries most load.

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

• Stresses in rigid pavements are due to

• Traffic loads – determine fatigue life of the pavement
• Environmental effects – curling and warping determine maximum
joint spacing for the pavement

• Warping stresses
• Locations: edge; interior; corner
• Wheel load related stresses
• Location: edge; interior; corner
• Shrinkage/expansion stresses
• Other stresses

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Warping Stress - Day Time Warping Stress - Night Time

(Slab surface temp>bottom temp) (Slab bottom temp>surface temp)

Constrained Transverse Joints

(Slab surface temp>bottom temp)

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8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

• Stresses are resisted by the flexural strength of the

concrete and not by any included reinforcing steel

• Stress due to curling and warping depend on the ratio

between the length of the slab L and the radius of relative
stiffness l.

• The radius of relative stiffness l is provided by:

where:

4 𝐸𝐷3 E = modulus of elasticity of concrete

𝑙= 12 1−2 𝑘 D = pavement thickness
K = modulus of subgrade reaction
 = Poisson’s ratio of concrete = 0.15

Warping Stress - Edge

By Bradbury
Where:
t = slab edge warping stress
E= modulus of elasticity of PCC
e= thermal coefficient of PCC
DT = temperature differential between the top and bottom of the slab
C= coefficient, function of slab length L and the radius of relative
stiffness, l

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Warping Stresses Coefficient

Warping Stress - Interior

By Bradbury
Where:
t = slab interior warping stress
E= modulus of elasticity of PCC
e= thermal coefficient of PCC
m= Poisson’s ratio for PCC
C1 = coefficient in direction of calculation
C2 = coefficient in direction perpendicular to C1

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Warping Stress - Corner

By Bradbury
Where:
t = corner warping stress
E= modulus of elasticity of PCC
e= thermal coefficient of PCC 
DT = temperature differential between the top and bottom of
the slab
m= Poisson’s ratio for PCC
a= radius of wheel load distribution for corner load
L= radius of relative stiffness

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Stress and deflection due to loading

• Can be determined from
• Closed-form formulas
• Influence charts and
• FE programs
• The formulas developed by Westergaard can be applied
only to a single wheel load

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Westergaard’s Model of Subgrade

Reaction

Slab Deflection to a Load

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Load Stress - Westergaard

Where:
b= equivalent radius of resisting section
a= radius of wheel contact area, and
h= slab thickness

Where:
W= wheel load
h= slab thickness
a= radius of wheel contact area
L= radius of relative stiffness
b= radius of resisting section

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Influence charts

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Slab Expansion/Contraction

Where:
z= joint opening (or change in slab length, in.)
C= base/slab frictional restrain factor (0.65 for stabilized bases;
0.80 for granular bases)
L= slab length (in.)
e= PCC coefficient of thermal expansion by aggregate type (e.g.,
6.0x10-6/F for gravel; 3.8x10-6/F for limestone)
Dt = the maximum temperature range
d= shrinkage coefficient of concrete (e.g., 0.00045 in./in. for
indirect tensile strength of 500 psi)

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

7.3. Design of dowels and joints – ERA manual

• Material quality is Joints in JPCP & JRCP

assumed to be: • Transverse joints
• Fc = 40 MPa • Contraction joints dowel bars
• Fy = 500 MPa 20 mm dia. @ 300 mm
spacing, 400 mm long for
slabs upto 239 mm thick and
25 mm dia. for slabs 240 mm
thick and more
• Expansion joints
• Contraction joints dowel bars
25 mm dia. @ 300 mm
spacing, 600 mm long for
slabs upto 239 mm thick and
32 mm dia. for slabs 240 mm
thick and more

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• Longitudinal joints
• Tie bars shall be 12 mm dia.
@ 600 mm spacing and 1000
mm long

• Construction joints
• Shall be coupled with other
joints for JPCP and JRCP
Transverse construction joint for CRCP
• For CRCP transverse
construction joints provide
each longitudinal bar a 700
mm long reinforcement bar
dia. 20 mm

8/9/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

7.4. Design of rigid pavements – ERA manual

• Design life up to 60 years

• Traffic in terms of ESAL

• Thickness design
• capping layer is required for
subgrade CBR 15% or less

• Subbase generally 150 mm

thick with CBR > 30 %
granular or cement treated

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• Joint spacing for JPCP &

JRCP

8/8/2012 Alemgena Alene, PhD CENG6302 - Ch7 MU-EiT

Concrete slab thickness and reinforcement

• JPCP & JRCP thickness

for laterally supported

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• Longitudinal reinforcement shall be

• CRCP thickness for
0.6% of slab cross-section 16 mm
laterally supported dia. Bar
• Transverse reinforcement shall
be12 mm diat @ 600 mm spacing

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• Additional thickness
without lateral support

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