Cement Energy and Environment

different grades of m1n1mum yield stress, tensile strength and % elongation. When ductile behaviour of the structure is important, as in earthquake resistance, ductility of steel is important. For enhanced corrosion resistance galvanized steel bars or fusion-bonded epoxy-coated bars can be used. A new addition in the list is stainless steel. It has been used for reinforcement in concrete in other parts of the world, notably Scandinavian countries and now proposed in the revisions of IRC Bridge Codes (IRC 21, IRC 18). A cost effective holistic approach is required; if stainless steel is being used, other parameters for corrosion protection should be relaxed. Aggregate Great challenges are being faced in quality aggregates for concrete constructions. Most specifications prescribe aggregate from natural sources conforming to IS: 383. In particular it is required that coarse aggregate shall consist of clean, hard, strong, dense, non-porous and durable pieces of crushed stone, crushed gravel, natural gravel or combination. Fine aggregate shall be natural sand, crushed stone, crushed gravel and combination, and Grading of Zone I, II and Ill are required. Arising primarily out of environmental concerns, aggregate from natural sources are becoming increasingly difficult, more so for river sand. An innovative approach to explore other alternatives is required . Some of these are; • Crushed rock manufactured sand, • Demolition waste and recycled concrete, • Bottom ash from thermal power stations, • Industrial wastes - Foundry wastes, copper slag, ceramic waste etc. Publications in ICI Journal and reports from R&D laboratories and Universities have highlighted use of many such alternatives. One alternative which has not received due attention is bottom ash from the boilers of thermal power stations. Its pozzolanic properties have been recently investigated in a collaborative programme between SINTEF, Norway and NCBM and NEERI in India. It is much coarser than fly ash, about 5 percent being retained on 1400 micron (1.4 mm) sieve, 50 per cent coarser than 212 micron 75 per cent coarser than 125 micron sieve size. Chemical and mineralogical compositions are similar to the fly ash from the same thermal power stations. When ground to fineness similar to the fly ash, bottom ash exhibited comparable pozzolanic properties for use as a mineral admixture in concrete. Its use as sand replacement should be explored. Adherence to grading zones of IS: 383 may not be achieved by these alternatives singly, nor is it necessary. Suitable combinations of materials from various sources; natural and industrial (wastes), along with binder system should result in desired workability, coherence and economy. Optimum combinations by particle packing theory, along with trials in mixes should be adopted. Water Quality requirements of water for mixing and curing concrete are specified in IS: 456. It is required that water for m1xmg and curing should be clean, free from organic and inorganic materials and substances deleterious to concrete and steel. pH value should be >6. Permissible limits of harmful salts and impurities are given in IS: 456. It is generally stated that potable water is fit for use in concrete. However, potable water or municipal water supplies are not available for constructions. In many constructions, water purification by RO system is being adopted. Sustainability Sustainable development is a socio-ecological process, characterized by the fulfillment of human needs while maintaining the quality of the natural environment indefinitely. The most frequently used definition of sustainable development is 'that meets the needs of the present generation without compromising the ability of the future generations to meet their own needs'. One aspect of the problem of sustainability is the consumption and depletion of material resources. Ecological footprint is a measure of human demand on nature. The eco footprint is equal to the land and marine area needed to regenerate the resources that are being consumed and to absorb the corresponding waste. Global Environment Outlook-4, a report recently released by UN Environment Programme (UNEP) states that today humanity's eco footprint is 40 per cent larger than what the planet can regenerate. In other words, it takes nearly one and a half years for the earth to grow, what human being use in one year. Clearly, this is unsustainable. The other important issue relates to emission of greenhouse gases, consequent 8