Cement Energy and Environment

New paradigms of quality Quality in construction, in its broadest sense, implies fulfillment of technical , technological , financial and other societal needs, which the constructed facility is intended to satisfy. If that be so, we need a 'performance'- based approach to quality. Quality should be expressed in terms of 'what quality concrete should ensure.' The end result should not be restricted only to technical goals, but also societal, environmental and economic. The list of desirable may include; • Adequate strength and load– bearing capacity, • Stability, ductility and serviceability incase of natural calamities and disaster, • Adequate durability and service life, • Adequate durability and assured service life, • Use of appropriate materials of construction, • Sustainability, • Scope of innovation, • Overall economy and low life-cycle cost. As will be explained , these goals are not exclusive and there is considerable overlap, in that, if one goal is achieved , it helps in attaining some other goal also. Design for strength and durability Present day approach to design of concrete structures, by and large, ensures that the structure will have adequate strength , load-bearing capacity and stability for the anticipated load, unless there are gross errors in design and detailing. The same confidence has to be extended to natural calamities and disasters like cyclones, heavy floods, hurricanes etc. From what evidences are seen of climate changes, triggered by global warming, one has to ensure prevention of total collapse of the constructions, if such calamities are encountered. This will call for greater emphasis on serviceability and ductility in the structures, rather than strength alone. Durability of concrete, even under anticipated service conditions, becomes a problem whenever the ingredients of concrete are not appropriate to the need, mix design is not competent and workmanship is inadequate. We have enough examples around us. Adequate durability should be a prime component of quality. Materials of construction There was a time, when the textbook description of concrete was 'made with cement, aggregate and water'. The times have changed and present day concrete incorporates many more ingredients, These are listed below; • Cements, PPC 66.6% Mineral PSC 8.3% admixtures - fly ash, ground granulated slag silica fumes, Chemical admixtures, • Aggregate • Water, • Steel Rebars, Prestressing. • Fibers- steel , polypropylene, Use of such additional ingredients came about in view of the considerable improvements these impart in the properties of concrete in fresh and hardened states. Depending upon the situation , their use should be uninhibited. Yet, many specifications are unduly restrictive in the use of some of these or other. Cementitious binders Take the case of cements. There are many varieties of cement permitted in IS Specifications, but the major production is of only three varieties; OPC, PPC and PSC. The latter two, collectively called blended cements, comprise the major share (Figure 1 ). Reservations about use of PPC and PSC in reinforced and prestressed concrete constructions are being gradually removed. In addition to cements, mineral admixtures • OPC • PPC o PSC 0 Other<: Figure 1. Production of Different varieties of Cement in India - 2008 - 09 data 6 r