The rigid pavements are generally made of Portland cement Concrete and therefore called CC Pavements. These pavements have very low flexural strength or flexural rigidity as they act like a slab and transfer the load to its below layers as slabs.
Types of Joints in Rigid Pavements
Joints are too important for the rigid pavements because the joints are responsible for reducing stresses developed due to temperature variations. There are two type of joints-
- Longitudinal Joints
- Transverse Joints
The Transverse joints are subdivided into three categories-
- Expansion Joints
- Contraction Joints
- Construction Joints
Shrinkage cracks generally develop in Rigid pavements supported on the base course during the initial period of curing, when the length or width of the slabs exceeds 4.5 to 5.0m. Therefore in pavements of width more than 4.5m, there is a need to provide a longitudinal joint. However, as the lane width of the highway pavements is generally 3.5 to 3.75m, longitudinal joints of CC pavements are provided between each traffic lane.
The longitudinal joints function as-
1. Contraction joints prevent the development of additional shrinkage in the longitudinal direction
2. Warping joints relieve part of warping stresses
3. Lane demarcation/markings in highways with two or more lanes
Tie bars are placed along the longitudinal joints of CC pavement in order to prevent opening up of the longitudinal joints in the due course.
Transverse joints are of three types-
Contraction joints are formed in the transverse direction of CC pavements at about 4.0 to 5.0 m or even lesser intervals so that the shrinkage cracks develop along these predetermined sections only. A considerable part of the load will get transferred across the contraction joint due to the interlocking effect across the fine shrinkage crack, provided these cracks do not get widened in due to course.
In order to prevent the widening of these fine shrinkage cracks, steel reinforcement may be provided across the contraction joints. If these contraction joints are formed without inserting steel reinforcement rods during construction, the pavement is called ‘Plain Jointed Concrete Pavement’.
Closely spaced contraction joints help to relieve part of the warping stresses developed due to temperature differential between the top and bottom of the CC pavement slab.
To accommodate the variation in the length of the CC pavements, expansion joints are provided in the transverse direction of the CC pavement at long intervals and after contraction joints. The expansion joints are formed as through joints across the full depth of the slab with about a 20mm gap between the two slabs.
In order to strengthen these joints of the CC pavements and to provide load transfer across the joints, suitable Dowel Bars are designed and installed during construction.
During the construction of CC pavements when the concreting work is stopped at the end of the day or concrete paving is suspended due to any other reason, a construction joint is formed. As the construction joints are formed as through joints across the full depth of the slab, it is necessary to provide suitably designed Dowel bars for load transfer.
As far as possible it is advisable to merge the construction joints with an expansion joint by suspending the concreting work at the nearest expansion joint so that the dowel bar system will be available for load transfer. If this is not possible, it is suggested that the construction joint may coincide with the nearest contraction joint and appropriate load transfer dowel bars are to be introduced.
Rigid Pavements: Objective, Advantage, Disadvantage, Components, and Affecting Factors
Flexible Pavements: Objective, Advantage, Disadvantage, Components, and Affecting Factors
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