From the word “rigid”, it is clear those pavements that are of a high strength. Rigid pavements are the laid surfaces that are constructed of high strength concrete on foundations having little resistance against live loads.
Rigid pavements provides only in area where sub-grade not provides an adequate support against load. This is mostly happens in regions where rain is in excess and due to this pore water pressure is in upper part of strata.
When water table will be near the surface of earth, then soil strength is very small, because of water table there are many air voids in the soil and we all know that with the increase in void ratio, strength of material drops.
What happen actually, when live load acts on the pavement then these air voids get closer and give a way to the movement of soil and when underlying soil moves then this creates a hollow space below the pavement. In these conditions do not go for flexible pavements.
Rigid pavements deflect very less because rigid pavements provides only where soil support is very little. In such cases we design a pavement that also contains enough beam strength too, so that it easily resist weight of vehicles and carry alone most structural capacity and only a small weight transfers to the underlying strata. Therefore, in design of rigid pavement most prominent factor is the structural strength.
Modulus of elasticity (ratio between stress & strain) of rigid pavement is higher than that of flexible pavements. This is because of the same reasons as explained earlier. If modulus not kept very high than this mean strains will be easily propagate in the pavement and when strains propagates then pavement will not remain rigid pavement.