Confluence of requirements for sustainable and durable concrete
  A.K. Mullick
  Sustainability and durability are among the important attributes of present-day concrete constructions. Sustainability demands careful exploitation of material, energy and environment resources, so as not to deprive the coming generations of the same. Durability of concrete is ‘its resistance to various deteriorating agencies that may reside inside the concrete itself, or be present in the service environment to which the concrete structure is exposed’. This paper examines the prescriptions common to both sustainable concrete and durable concrete, of which there are many. It also examines some measures which serve the requirements of sustainability but may affect durability. Prescription of durability of concrete involve control of water/binder ratio, adequate cover depth, proper workmanship, use of special steel etc., all of which are independent of sustainability considerations. One important consideration is use of industrial wastes as mineral admixtures which improve durability, as described in the paper. This is an area, where there is complete harmony in the requirements of durability and sustainability of concrete. However, the proportion of fly ash as replacement of cement has to be restricted, lest the carbonation may increase, affecting durability. Use of manufactured aggregate is now permitted in IS 383. Most of the substitute materials are investigated in terms of effect on the compressive strength of concrete, and on workability; effects on durability are seldom investigated. The paper presents results of use of recycled concrete aggregate as replacement of natural aggregate up to 100 percent, on various durability parameters. Restrictions in IS 383 have to be appreciated from this point of view. Recycled water can be used for making and curing concrete, provided it satisfies all the requirements of IS 456.