Rigid pavements

CONSTUCTION OF RIGID
PAVEMENTS
1

RIGID
PAVEMENTS???
 As the name implies, rigid pavements are rigid i.e, they do not ex much
under loading like flexible pavements.
 They are constructed using cement concrete. In this case, the load carrying
capacity is mainly due to the
 rigidity ad high modulus of elasticity of the slab (slab action). H. M.
Westergaard is considered the pioneer in
 providing the rational treatment of the rigid pavement analysis.2

WHERE IS RIGID
PAVEMENT PROVIDED????
Rigid pavements are usually provided when road stretch is
subjected to adverse conditions:
 Very heavy rainfall
 Poor soil conditions
 Poor drainage
 Extreme climatic conditions
 Combinations of some of these conditions which may lead to
development of cracks inn pavements
3

Material for construction of CC
pavements
 PORTLAND CEMENT
 The type of cement that may be used for the preparation of PQC and
construction of cement concrete road construction pavement are:-
 (i) Ordinary Portland cement of 43 Grade.
(ii) Ordinary Portland 53 Grade.
(iii) Portland Pozzolana cement with fly ash content up to 20% by weight.
(iv) Portland slag cement. However most commonly used cement for the
cement concrete road construction is ordinary Portland cement of 43 Grade.
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pavements
 COARSE AGGREGATE VALUES OF CEMENT CONCRETE ROAD
The coarse aggregate that is used for PQC of cement concrete road
construction should fulfill the following requirements apart from this the
maximum size being limited to 31.5 mm.
6

FINE AGGREGATES USED IN ROAD
CONSTRUCTION
Fine aggregate consists of clean natural sand or
crushed stone sand or a combination of both;
the fine aggregate shall be from clay, coal and
lignite. The fine aggregate shall be well graded,
with 100 percent passing 10 mm sieve. The IRC
has suggested four gradations of fine aggregate
for the preparation of the PQC mix.
pavements
7

Desirable limits of Important properties
Los angles abrasion value 30% max
Aggregate impact value 30% max
Aggregate crushing value 30% max
Water absorption Less than 3.0 percent
Soundness test after five cycles: loss in
weight after 10 cycles
Less than 12 percent
Loss of magnesium sulphate Less than 18 percent
8

WATER
Water used for mixing of the cement concrete, and also that used for curing of the cement
concrete road construction shall be clean and portable. The water should be free from salt, acid,
oil and other organic matter.
 ADMIXTURE IN CEMENT CONCRETE ROAD CONSTRUCTION
Commonly used chemical admixture in the cement concrete road construction are:
(i) To improve the workability of the concrete; a suitable air entraining agent may
be used.
(ii) To provide an adequate extension of setting time of the concrete mix without
adversely affecting the other desirable properties of the concrete; super-plasticizers
which retard the setting time may be used. The total quality of chemical admixture
used is limited to a maximum of 2.0 %by weight of the cement or used.
 STEEL
Steel dowel bars with yield strength 2400 kg/sq. cm or 240 Mpa is used for the load transfer
across in the expansion joints and construction joints of cement concrete roads. Plan or
twisted steel bars are used as tie bars at longitudinal joints. All steel rods shall be coated
with epoxy paint for protection against corrosion.
9

Different Types of CC
Pavements
Jointed Plain Concrete Pavement (JPCP)
– does not use any reinforcing steel
 Jointed Reinforced Concrete Pavement (JRCP)
– Reinforcing steel placed at mid height and discontinued at the joints.
 Continuously Reinforced Concrete Pavement (CRCP)
– This method is very costly and generally not used in India.
 Pre-stressed Concrete Pavement (PCP)
– Comprises new and innovative construction methods
Among these Plain CC pavements are most commonly used.
10

Construction Process
The construction of concrete pavement involves sequential
construction of subgrade,
sub-base/ base and the concrete slab. These are discussed
in the following.
 Subgrade preparation
Subgrade preparation involves
cleaning, earthwork (excavation or filling of soil,
replacement of weak soil, soil stabilization etc.) and
compaction.
Where the concrete layer is laid directly over the subgrade,
the subgrade is moist at the time concrete is placed. If the
subgrade is dry, water could be sprinkled over the surface
before laying any concrete course, however, care should
taken so that soft patches or water pools are not formed at
the surface (IRC:15-2002,Chakroborty and Das 2003). As
an alternative arrangement, concreting could be done over
a water proof polyethylene sheet, and in that case
moistening the subgrade surface becomes redundant. This
polyethylene sheet acts as a capillary cut-off layer (IRC:15
2002). Figure-31 presents a photograph of subgrade
construction in progress.
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 Fixed form paving system
 In fixed-form paver system, generally, separate powered machines for spreading, compacting
and finishing are used. The spreader spreads concrete evenly through reversible auger to
the desired surcharge level(O'Flaherty 2002). The rotary strike-off paddles trim minor
irregularities in the surface of the surcharge concrete and adjusts with the carriage-
way cross-slope . The compaction beam applies vibration to the concrete with pre-designed
amplitude and frequency (O'Flaherty 2002). This vibration also helps to put the dowel and tie
bars at their desired positions (for a single layer construction).
 The wet formed joint groove is made by introducing vertical cut immediately after compaction
is over and inserting a preformed cellular permanent strip . As an alternative, saw joint
groove can be made after the concrete is sufficiently hardened and can maintain the sharp
edge itself (O'Flaherty 2002).
 The finishing of the surface is made, generally, with a pair of finishing beams . The leading
beam vibrates and smoothens the surface, and the rear beam acts as float . The beams are
oriented obliquely so that it causes less damage to the joints (O'Flaherty 2002).
12

Slip form paving system
 Slip-form paving machine is a self-propelled system that can automatically spread, trim,
compact and finish the surface in a synchronized manner through its feedback sensors.
Placing of dowel/ tie bars at their pre-designed locations are done by the slip-form pavers.
The introduction of joint grooves, surfacing texturing and spraying of curing compound etc.
are done by the equipment those follow the paver (O'Flaherty 2002).
 Slip-form paver requires guide-wires, parallel to edge of construction and maintained at fixed
height, installed on the both side. The alignment of the slip-form paver is controlled
automatically with respect to the guide-wires. Correct and precise alignment of the guide-
wires is therefore extremely important. The hopper/ spreader maintains a constant surcharge
of the concrete above the conforming plate level. The conforming plate, vibrators, strike off
paddles and the finishing screed gives the final shape of the concrete pavement (O'Flaherty
2002). Figure-35 explains schematically the operation of a typical slip-form paver, and
Figure-36 a photograph of concrete pavement construction by a slip form paver.
13

Concrete curing
Curing is a process in which requisite moisture content and temperature is maintained so that
concrete achieves its design strength through hydration of cement. For initial curing, curing
compound with high water retentivity may be spread over the finished surface to prevent rapid drying
of water. For final curing, continuous ponding or moistened hessain/ gunny bags should be kept for
about a fortnight (refer Figure 38). As an alternative arrangement to ponding, impervious liquid maybe
spread over the surface so as to restrict evaporation of water from the laid concrete. Forms are
removed from the freshly prepared concrete layer after about curing of fourteen hours (IRC:15
2002, Chakroborty and Das 2003).
Texturing
Finished concrete has a smooth surface; texturing of concrete surface is done to impart
required skid resistance to the concrete surface. The texturing is done by means of wire brushing or
grooving along the transverse direction. Initial texturing may be done at the time of construction of the
paver itself (refer Figure 37). Final texturing is done no sooner the sheen of the concrete surface goes
off ( Swanlund and Vanikar 2002 ).
15

JOINTS IN CC PAVEMENTS
 Joints are the discontinuities in the concrete pavement slab, and help to release
stresses due to temperature variation, subgrade moisture variation, shrinkage of
concrete etc.
 There are various types of joints in concrete pavement, e.g. contraction joint,
construction joint, expansion joint and warping joint. Fig. 3 schematically shows
position of various joints. The functions of these joints are as follows:
 Longitudinal joints(parallel to traffic flow)
 Transverse joints(perpendicular to traffic flow)
 Contraction joints
 Expansion joints
 Construction joints
16

Longitudinal joints
 During initial period of curing ,shrinkage cracks usually develops in CC pavements
when length or width of the slabs exceeds 4.5 to 5 m width or more.
 Hence longitudinal joints are provided whose spacing depends on width of traffic
lane . For instance if width is 3.5 or3.75 , then spacing of longitudinal joints is also
3.5 or 3.75m respectively.
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Construction joints
Construction joints are placed in a concrete slab to
define the extent of the individual placements,
generally in conformity with a predetermined joint
layout.
Construction joints must be designed in order to
allow displacements between both sides of the slab
but, at the same time, they have to transfer flexural
stresses produced in the slab by external loads.
Construction joints must allow horizontal
displacement right-angled to the joint surface that is
normally caused by thermal and shrinkage
movement. At the same time they must not allow
vertical or rotational displacements. Fig.1
summarizes which displacement must be allowed or
not allowed by a construction joint.
19

CONTRACTION JOINTS
 These are purposely made weakened planes which relieve the tensile
stresses in the concrete Caused due to changes in the moisture content
(Drying shrinkage) and/or temperature and
 Prevent the formation of irregular cracks due to restraint in free
contraction of concrete .
 Purpose of joints in Concrete Roads
1. To absorb expansion & contraction due to variation in temperature.
2. To avoid warping of slab edges
3. To grant facility in construction .
20

Effects of reinforcement in concrete22

WORKING OF EXPANSION JOINTS :
During hot climate CC slab expands
towards the gap provided at expansion
joint, due to which filler board and joint
sealer gets compressed and pushed up.
Dowel bars also move along with the slab,
occupying the space in the metal cap
attached at the end of each dowel bar.
AND, During cold climate slabs contracts
and gap increases and dowel bars also
move along with slab.
The compressed filler board may partly
recover and joint sealer moves down.
23

Joint Filler and Sealer
 Joints form break in cement concrete pavement and the can allow the infiltration of
water and the ingress of stone grits. Thus, the joint spaces are first filled with
compressible filler materials at first and the top of the joints are sealed using a
sealer.
 Joint filler should posses the following properties:
 Compressibility
 Elasticity
 Durability
 Joint sealer should posses following properties:
 Adhesion to cement
 Extensibility without fracture
 Resistance to ingress of grit
 durability
24

Types of joint filler
Soft wood
Impregnated fiber
Cork or cork bound with bitumen
25

Types of joint sealers
 Bitumen is used along
with mineral filler as a
sealing compound
 Rubber bitumen
compounds
 Air blown bitumen
26

QUALITY CONTROL DURING
CONSTRUCTION:
1. CA samples collected should be tested to specified tests in the laboratory to decide
suitability.
2. Grading of CA and FA for mix is checked and compared with specified gradation.
3. Samples of fresh CC mix are collected ,cube and beam specimen prepared and
tested according to standard test and checked with acceptance criteria.
4. Side slabs of pavements is checked to find hungry/honeycombed surface such
surfaces are finished with cement mortar.
5. Regularity of finished pavements is checked with a 3m straight edge, 6 to 12 hours
after laying , maximum permissible number of irregularities of 4 mm and 7 mm sizes
in a 300 m stretch are 20 and 2mm.
6. Unevenness index or roughness index is measured using bump indicator, along the
wheel path of each lane; the average value of unevenness index shall not exceed
2200 mm/Km length of highway.
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OPENING TO TRAFFIC
The entire surface of newly laid pavement is carefully examined for :
1. Fine cracks have developed on surface
2. Non-uniform settlements of CC slabs has taken place near
abutments or along high embankments.
If any such defect is noticed ,then corrective measures may be taken
up.
A newly constructed CC pavement stretch shall be opened to traffic
only after a minimum curing of 28 days.
28

References
 NPTEL web courses, Transportation, Modules
 IRC SP 062: Guidelines for the design and construction of Rigid
pavements
 Highway and Transportation engineering, S K Khanna and CEG Justo
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Rigid pavements

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Rigid pavements