Types Of Flexible & Rigid Pavement

Failures

Failure In Rigid Pavements

A Rigid Pavement failure is observed by the development of structural cracks of break resulting in progressive subsidence of some portions  of pavements. Moderate irregularities in the supporting layers beneath the cement concrete pavements are sustained due to inherent bending strength of these pavements. Rigid pavements therefore are capable of withstanding slight variations in the underlying support and they bridge the localized gaps moderately. It is the combination of many factors that induce the failure conditions in the rigid pavements.

SCALING OF CEMENT CONCRETE 

Scaling of rigid pavement simply means, peeling off or flaking off of the top layer or skin of the concrete surface. This may be due to the following reasons

• Improper mix design
• Excessive vibration during compaction of concrete
• Laitance of concrete
• Performing finishing operation while bleed water is on surface

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.

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 in-compressible material below concrete slab
• Insufficient strength of concrete slab near joints
• Freeze-thaw cycle
• Excessive stress at joint due to wheel load

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.

PUMPING

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

Failure In Flexible Pavements

A Flexible Pavement failure is defined by formation of pot holes, ruts, cracks, localized depressions and settlements. The localized depression normally is followed with heaving in the vicinity. The sequence develops a wavy pavement surface. The failure of any one or more components of the pavement surface or longitudinal ruts and shoving. Pavement unevenness may itself be considered, as a failure, when it is excessive.

Ruts

The longitudinal depressions or cuts in flexible pavement is known as ruts. These are usually formed ion earth or W.B.M roads of one lane width due to repetitive traffic wheel loads on the same location, particularly under wheeled traffic.

Pot Holes

The isolated depressions, more or less circular in shape formed in flexible pavements are called pot holes or patches. These are usually formed in all types of flexible pavements due to disintegration of road metal or lack of binding surface course with the underlying base.

Frost Heaving

A localized heaving up of pavement portion is known as frost heaving.

The water which may find access to pavement structure freezes in cold climates. The expansion accompanying this frost action causes upheaval which in turn may crack the pavement surface.

Shear Failure Cracking

The formation of a fracture or cracking due to upheaval of pavement portion followed by a depression called shear failure cracking. This type of failure occurs due to localized weakness in the pavement.

Longitudinal Cracking

The formation of cracks in the longitudinal direction of a road pavement is called longitudinal cracking.

This failure is caused due to frost action, different volume changes in sub-grade, settlement of filling material or due to sliding of side slopes.

Map Cracking

The development of irregular cracks, usually formed on bituminous surfacing is called map cracking.

This type of flexible road failure is due to excessive wear of the road surface or due to localized weakness in the underlying base course.