Designing a reinforced concrete structure there are only two main considerations, the amount of reinforcement and the strength of the concrete. To achieve required strength, proper cover (rebar spacing) is specified in design code as in IS Code-IS 456-2000 but how this cover is obtained is ignored. Too large or too small cover causes problems. To use any available materials like broken marble or tile pieces or piece of aggregate is crude and amateurish method and at the cost of strength and durability.
Polypropylene and PVC covers are also available but these are foreign body materials to concrete, fails to essentially form a permanent bond with concrete. Thermal coefficient of expansion is different with concrete. Water vapours entering in the structure, hair cracks are developed which may leads to structure failure. Thus use of Polypropylene and PVC covers is not preferred throughout the world.
DVGW (Deutsche Vereinigung des Gas und Wasserfaches)(German Association of Gas Hydraulic Engineers) in their technical regulation sheet No W311 have recommended use of only concrete covers but these covers must be fibre reinforced. IS Code 456-2000 recommends that the covers be made with aggregate of M-35 plus. Concrete covers are fire resistant, thus prevent passage of fire to reach at rebars.
To spread the cult of use of concrete cover blocks, most of big cement manufacturing companies like Ultrateck Cement Ltd, India Cement Ltd and Binani are proving cover blocks to consumer through their dealer’s network at subsidised rates or at free of cost.
Thus importance of use of covers is well identified by the cement manufacturing companies but some of the project executives like engineers and architects yet to be made aware themselves about importance of cover block utilization.
Thus it now worldwide accepted fact that only concrete covers is used in all type of structure with proper cover heights. In India rebar spacing is also defined in IS Code IS 456-2000.