Cement, Energy and Environment

grading of blended cements has not affected the growth of fly ash based PPC and the maintenance of a steady share of PSC in the Indian market. On the contrary, there are apprehensions that in the 2020s there could be adverse impacts on resource conservation and CO 2 emissions reduction strategies of the industry and country at large. In addition, it may not technically be a correct strategy for going ahead with durability design of concrete structures. The apprehensions emanate from the fact that the production of higher strength grades of blended cements would involve reducing the proportion of fly ash or slag in corresponding cements, or grinding of cements finer, or use of some relatively expensive grinding aids/ chemical additives, or a combination of these measures. None of the above steps are conducive for sustainability. Utilization of Fly Ash As already stated, the fly ash based PPC is the predominating type of cement produced and marketed in India. In fact, the Indian cement industry has been successful in providing a crucial solution to the environmental problem caused by increasing generation of fly ash from the coal-based thermal power plants. The details of generation and utilization of fly ash in 2017-18, as reported by the Central Electricity Authority, are given in Table 2. The current fly ash utilization of 67% of the total quantity generated includes primarily the production of PPC (~26%), bricks and tiles (~9%), concrete (<1%), and some other uses in smaller quantities as shown in Fig.2. The use pattern still leaves almost one- third of fly ash unutilized, which amounts to about 65 Mt. The past trends of generation and use of fly ash are shown in Fig.3. Quantities generated during the previous three years were 184 Mt in 2014-15, 177 Mt in 2015-16 and 169 Mt in 2016-17 and the corresponding amounts used were 103 Mt (56%), 108 Mt (61%) and 107 Mt (63%) respectively. The utilization of fly ash in 2017-18 has been the highest so far. Despite the fluctuations in generation of fly ash, it is evident that about 60- 70 Mt of fly ash remains unutilized every year, a major part of which could form an important resource for the massively expanding cement and concrete industry. The trend of use of fly ash in cement, and negligibly in concrete directly, is shown in Fig.4, which shows a flat trend in the past few years (~40 Mt). In 2017-18 there is some increase in the use of fly ash in cement to about 50 Mt but it is somewhat early to predict this increase as a rising trend. With the grading of PPC, a serious concern that surfaces is whether the full potential of the increasing cement production in the country to absorb more and more of fly ash would be throttled, creating further environmental problems. Consideration of Clinker Quality and Limestone for Blended Cements In cement chemistry fly ash is regarded as a pozzolanic ma t e r i a l , wh i l e GGBS i s considered as a cementitious material. The mechanism of hydration of these two SCMs is different and the Table 2. Summary of fly ash generation and utilization in 2017-18 Details of generation Quantity No. of reporting power plants 167 Installed capacity 177 GW Coal consumed 625 Mt Fly ash generated 196 Mt Fly ash utilized 132 Mt Percentage utilized 67 % Average ash content in coal 31.44% 19