A layer of waterproof (or separation) membrane is normally placed between sub-base and concrete slab for the following reasons:
(i) It prevents the loss of water from cement paste which affects the strength of concrete slab.
(ii) It enhances the movement of concrete slab relative to sub-base layer and reduces the frictional forces developed at their interface.
(iii) It avoids the possibility of active aggressive agents from soil water being attached to the concrete slab.
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(iv) It prevents the intermixing of freshly placed concrete with loose materials on the surface of sub-base.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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