IMPROVEMENT OF MECHANICAL PROPERTIES OF RIGID PAVEMENTS full report

[dipin]

IMPROVEMENT OF MECHANICAL PROPERTIES OF RIGID PAVEMENTS
[attachment=1801]
INTRODUCTION
Transportation-basic infrastructure-development

Rigid and flexible

Basic neccesity-stable against loads

Rigid offers more strength load

But change in temp. warping up and warping down

To relieve stress-joint

Joint from the weaker plane and most of defects occur there

Increase the mechanical properties such as load carrying capacity and cracking resistance

Methods for improvement


Rigid Pavement
Consist of subgrade, (base course) and Cement concrete slab

It resists minor deformations

Got more strength and life than flexible pavements


JPCP

most common type

control cracks by dividing pavement into individual slabs seperated by contraction joints

3.7m wide and 6.1m long
Use of dowel bar


JRCP
Control cracks by dividing pavement into individual slabs seperated by contraction joints but longer than JPCP
Uses reinforcing steel


CRCP

Does not require any contraction joints

Use reinforcing steel for crack control


JOINTS IN RIGIDPAVEMENTS
TRANSEVERSE JOINTS
Expansion joints
Contraction joints
Warping joints
Construction joints


EXPANSION JOINTS
Provided to allow for the expansion of the slabs

Also permit the contraction of slabs

Provide at interval of 50-60m in winter and 90-120m in summer

In rough interface spacing-140m

The approximate gap width of joints 20-25mm


CONTRACTION JOINTS

Provided to permit the contraction of the slabs

Load transference at the joint is provided through the physical interlocking by aggregates projecting out at the joint faces

Max.Spacing for unreinforced concrete slab-4.5m and for reinforced concrete slab of thick-20cm-14m


LONGITUDINAL JOINTS
Provide in cement concrete roads

Provide to prevent the longitudinal cracking

Act as hinge to maintain the two slabs together-at the same level


WARPING CRACKS
If joints are not well designed-accommodate warping of slabs at edges - results development of excessive stresses and cracking at the edges in an irregular pattern

No structural defect due to the warping cracks if proper reinforcement is provided at the longitudinal & transverse joint as it take care the structural adequacy


BLOWUP/BUCKLING
Occur in hot weather
At a transverse crack or joint
Insufficient width
Caused by infiltration of incompressible material into the joint space
A localized upward movement of the slab edges(buckling) or shattering will occur in the vicinity of the joint


DOWEL BARS
Short mild steel bars
Provides mechanical connection between slabs without resisting horizontal joint movement
Half length is bounded in one cement concrete slab and remaining in other.
Keep free for the movement during expansion and contraction of the slabs
32 -38 mm diameter, 460 mm long and spaced 305 mm apart


REINFORCING STEEL
Used to provide load transfer
Transverse and Contraction joints are often omitted
Since there are no joints the PCC cracks on its own and the reinforcing steel provides load transfer across these cracks
Unlike Dowel Bars- it is bounded to the PCC on either side of the crack in order to hold the crack tightly together


TIE BAR
It is used across the longitudinal joint of cement concrete pavement
It ensure two adjacent slab to remain firmly together
These are not designed to act as load transfer device
Max. tensile force equal to the force required to over come frictional force between the bottom of the adjoining pavement slab and the soil sub grade
Force is considered from joint location to the subsequent joint or free edge


AGGREGATE SELECTION
Research was conducted-three different aggregate types of lime stone, river gravel and trap rock and two different sizes of 25mm and 38mm
Fracture energy represents the cracking resistance, Power Spectral Area Parameter(PSAP)
represents concrete surface roughness and indicates its ability to transfer load across a cra


USES OF FIBERS IN CONCRETE PAVEMENTS
Fibers added in sufficient volume to plain concrete improve properties, fracture toughness and crack width control

Fiber used improve cracking performance of concrete pavements, reduce required slab thickness and increase the allowable joint spacing


CONCLUSION
Concrete pavements are preferred now a days due to its durability and good riding surface.
Inorder to improve the load transfer capacity several methods can be adopted. Conclusion drawn from present study are:
Load transfer across transverse joint can be carried out through dowel bars .
Tie bars help to hold the adjacent slabs together in the case of longitudinal joint.