Q. Function of waterproof (or separation) membrane for concrete carriageway

A layer of waterproof (or separation) membrane is usually placed between sub-base and concrete slab for the below reasons:

(i)  It prevents loss of water from cement paste that affects the strength of concrete slab.

(ii) It improves the movement of concrete slab relative to sub-base layer and decrease the frictional forces developed at their interface.

(iii)It avoids the possibility of active aggressive agents from soil water being attached to concrete slab.

(iv) It prevents intermixing of freshly placed concrete with loose materials on the surface of sub-base.

Fig: Location of separation membrane in concrete carriageway