Ans :Permanent deformation in soil subgrade The accumulated permanent or non- recoverable deformation of the subgrade along the wheel paths of heavy vehicles in formation of longitudinal ‘ruts’ on the pavement surface. The depth of these longitudinal ruts or the ‘rut depth’ continues to increase until the ruts are filled up and pavement structure is strengthened.

1. Longitudinal Cracking: This types of cracks extents to the full thickness of pavement. The following are the primary causes of longitudinal cracking.

• Differential volume changes in subgrade soil

• Settlement of fill materials

• Sliding of side slopes.

BLEEDING: Excess bituminous occurring on the pavement surface causes bleeding. Bleeding causes a shiny, glass like reflective surface that may be tacky to the touch. Formation of waves &corrugation: Transverse undulation appear at regular intervals due to the untestable course caused by stop- and go traffic.

Lack of binding with lower layer: When there is lack of binding between surface course and underlying layer, some portion of surface course losses up materials creating patches and potholes. Slippage cracking is one form of this type of failure. Lack of prime coat or tack coat in between two layers is theprimary reason behind this type of failure.

RIGID PAVEMENT FAILURE

Faulting in rigid pavement: The difference in elevation between the joints is called as faulting. The main cause of failure in rigid pavement due to faulting are:

• Settlement of the pavement that is caused due to soft foundation

• The pumping or the erosion of material under the pavement, resulting in voids under the pavement slab causing settlement

• The temperature changes and moisture changes that cause curling of the slab edges. Polished Aggregate in rigid Pavements: The repeated application leads to this distress. These are the failure in rigid pavements caused when the aggregate above the cement paste in the case of PCC is very small or the aggregate are not rough or when they are angular in shape that can not provide sufficient skid resistance for the vehicles. Shrinkage Cracking: These are hairline cracks that are less than 2 m in length. They do not cross the entire slab. The setting and curing processes of the concrete slab results in such cracks. These are caused due to higher evaporation of water due to higher temperature cracks. Improper Curing can also create shrinkage crack’s in rigid pavements