Flexible and rigid pavements

Pavements come in two families. A flexible pavement has bituminous surface layers over granular or stabilised bases. It spreads a wheel load through the layers in a widening cone, so each layer only has to cope with the stress at its own level. A rigid pavement uses a concrete slab that acts like a stiff plate and spreads the load over a wide area by bending.

Flexible pavements are cheaper to build and easy to overlay and repair in stages. They are sensitive to water and heavy axles, and need periodic resurfacing. Rigid pavements cost more at first but last longer with less maintenance, suit heavy traffic, bus bays and toll plazas, and resist oil spills. They need joints to control cracking.

Design methods differ. Flexible pavement design in India follows IRC:37, which uses a mechanistic-empirical approach checking strains that lead to fatigue cracking and rutting. Rigid pavement design follows IRC:58, which checks slab stresses from load and temperature.

Composite pavements, such as asphalt over concrete, mix the two.