USE OF FLYASH AS PARTIAL REPLACEMENT OF CEMENT WITH SPECIAL REFERENCE TO NAGARJUNASAGAR PROJECT

Abstract

Ely ash is an industrial waste, resulting from the combustion of pulverised coal in thermal power plants and is known to have pozzolanaic properties by 'virtue of which it can be utilised as cheap construction material. Ely ash has come into use as a pozzolanas an admixture and as fine aggregate recently in India, though it has been used for many decades in other advanced countries like U.C.A; Japan, France etc. Fly ash from I3ok aro thermal power plant was used in the m as s concrete work of Rihand Dam for the first time in India and since then it is being adopted as partial replacement of cement in mortars and concrete for the construction of masonry dams, hydraulic structures, lining of canal works and many building works in different parts of India. It has been observed that when fly ash is used as a single replacement of cement in mortars and concretes, its strength is reduced at early ages and it is only after 60 to 90 days that strength comparable to, the control mix (mix with-out fly ash) and even more under controlled conditions may be obtained. P'br building and R.C.C. works in which early stren-gth becomes an important factor, use of fly ash could not be advocated due to the very fact that fly ash concrete mix deve-lops its full strength at latter ages. with the increasing use of fly ash, necessity has been felt to design the fly ash concrete mixes for all types of concrete works mass as well as structural. With this view,. intensive research work has been done in India and other coun-tries to evaluate the methods of mix design with fly ash by which early strength just like plain. cement concrete can be obtained. Several modified .mix design procedures have been developed to design the fly ash concrete. However, none of the methods could be adopted directly for aall, the fly abhes and for all the proportions of mixes and they can be taken as guide to develop a mix design for other fly ashes and. mix. It was foundthat by using fly ash in excess of its replacement of cement, it acts as an additional material, gives more paste for reaction and gives equal or more strength at all ages. The scope of the dissertation is braodly divided into two parts. Part I contains three Chapters mainly covering the academic background for utility of fly ash as construction material; basic properties of reactivefly ash; and different methods of mix design for fly ash concrete. In these chapters work done in various Indian Laboratories has been analysed. The lime reactivity tests show that increase in carbon content adversely affects the strength and quality of fly ash for other uses also. Increase in fineness of fly ash results in increase in strength and improvement in the quality of fly ahs. Lime reactivity test for the same fly ash gives different results when the method of test is different and also on the quantity of Mgo and CaSDj+ present inthe cement. Hence the lime reactivity test is not always an index for suitability of fly ash as partial replacement of cement...