Cement, Energy and Environment

After the advent of the Portland cement, India was one of the foremost countries to formulate a national standard on Portland Slag Cement (PSC: IS 455), way back in 1953, based on ground granulated blast furnace slag (GGBS) from one of its own steel plants. When seen in the context of global developments, the history of introduction of PSC in India is especially interesting. Germany is regarded as the pioneer in the use of slag in cement and had set up the Eisen Portland Cement Association in 1901. But it is reported that even in 1930, the use of Eisen Portland Cement was limited to only one million tonne, which had increased to 7.5 million tonne in 1961. Use of slag in cement caught up in other European countries including the UK and the then USSR in subsequent periods. In this background, the efforts of early 1950s in India to standardize and produce PSC are worth noting. The Indian standard has been revised/reaffirmed five times between 1953 and 2015 and the current provision of clinker substitution by GGBS stands at 25-70%, although the actual level of substitution in the PSC producing plants generally lies in the range of 40-50%. The introduction of Portland Pozzolana Cement (PPC) followed within a decade with the national standard (IS:1489) released for the first time in 1962. The product was essentially developed on the basis of calcined clay as the pozzolana, as India does not have occurrences of natural pozzolanic substance. While the introduction of PSC in the market was a result of a technological pull in the 1950s, the initiation of PPC was prompted by the market push created by the gap in demand and supply in the country at that point of time. From late 1980s India started facing the problems of fly ash generation from the power sector and in 1991 the PPC standard was split into two parts: Part 1 covering pozzolana cement manufactured by using only fly ash as pozzolana, and Part 2 covering pozzolana cement manufactured by using either calcined clay or a mixture of calcined clay and fly ash. Including the above major revision, the PPC standard has been revised four times till 2015, and the current level of clinker substitution in fly ash based PPC stands at 15-35%. The thrust of the industry has all along been to maximize the clinker substitution by fly ash so as to reach its upper ceiling. The revision/reaffirmation of Part 2 of the PPC standard has followed the same time sequence but the clinker substitution level by pozzolanas has been kept at 10-25%. It may be relevant to mention that the PPC Part 2 standard has not received much attention from the industry for production purposes due to abundant generation of fly ash in the country, although the kaolinitic clay is recognized for its potential as a pozzolanic substance.. While the OPC standards (IS 269:2015) have three distinct grades on the basis of 28-day compressive strengths in mortars, the PSC and PPC standards continued to have till 2018 a single grade of minimum compressive strength in mortars similar to the 33-grade of OPC. Interestingly, notwithstanding the absence of strength grading in the blended cements in India for over several decades, the transformation of the product mix in the country had been phenomenal, as shown in Fig.1, during 1978-2001. Thereafter, in the first decade st of the 21 century, the product mix had changed further in favor of blended cements till 2017 (Table 1). 17