Performing finishing operation while bleed water is on surface
2. Shrinkage cracks
Formation of hairline shallow cracks on concrete slab is the indication of shrinkage cracks.
Shrinkage cracks develop on concrete surface during the setting & curing operation. These cracks may form in longitudinal as well as in transverse direction.
3. Joint spalling
Joint spalling is the breakdown of the slab near edge of the joint. Normally it occurs within 0.5 m of the joints. The common reasons for this defect are
Faulty alignment of incompressible material below concrete slab
Insufficient strength of concrete slab near joints
Excessive stress at joint due to wheel load
4. Warping cracks
In hot weather, concrete slab tends to expand. Therefore the joints should be so designed to accommodate this expansion. When joints are not designed properly, it prevents expansion of concrete slab and therefore results in development of excessive stress. This stress cause formation of warping cracks of the concrete slab near the joint edge.
This type of crack can be prevented by providing proper reinforcement at the longitudinal and transverse joints. Hinge joints are generally used to relieve the stress due to warping.
When material present below the road slab ejects out through the joints or cracks, it is called pumping. When soil slurry comes out it is called mud pumping.
The common reasons for this defect are
Infiltration of water through the joints, cracks or edge of the pavement forms soil slurry. Movement of heavy vehicles on pavement forces this soil slurry to come out causing mud pumping.
When there is void space between slab and the underlying base of sub-grade layer
Poor joint sealer allowing infiltration of water
Repeated wheel loading causing erosion of underlying material
Pumping can also lead to formation of cracks. This is because; ejection of sub-grade material below the slab causes loss of sub-grade support. When traffic movement occurs at these locations, it fails to resist the wheel load due to reduction of sub-grade support and develops cracks.
This type of defect can be identified when there is presence of base or sub-grade material on the pavement surface close to joints or cracks.