Cement, Energy and Environment

on reducing the CO 2 emissions. The impacts are seen for reduced content of cementitious material as well as for increasing the proportion of SCMs in the cementitious material per unit volume. It may be relevant to mention here that the emerging practice of the Ready-Mixed Concrete suppliers to blend cement with SCMs at the concrete plants should be encouraged as long as it is done with reliable proportioning and after conducting the required performance tests so that there is full compliance with the existing codes of practice. But it must be borne in mind that when the SCMs are interground or blended by the cement supplier, there is a greater level of quality control over the final product with less potential for incompatibilities and proportioning mistakes. The technical understanding and co-operation between the cement producers and concrete suppliers have to be extensive enough to encourage high volume addition of SCMs. Need for Blended Cements for Low-carbon Transition of the Indian Cement Industry It is widely known that the World Business Council for Sustainable Development (WBCSD) laid out a roadmap for low-carbon transition of the Indian Cement Industry with the involvement of Cement Sustainability Initiative (CSI), which includes several major Indian cement companies, in 2013, using 2010 as the reference year. This roadmap has been reviewed in 2018 and the review has brought out that the clinker factor has come down to 0.71 in 2017 from 0.74 in 2010. This and other measures taken resulted in 5% reduction in CO 2 emissions between 2010 and 2017. The target for the year 2050 is set at achieving the specific direct CO emissions 2 intensity of 0.35 t/t of clinker, about 45% lower than 2010 level. Hence the task before the industry is gigantic. While there are many measures contemplated to achieve this extent of CO emissions 2 reduction, it is evident that the reduction of CF to about 0.58 with the help of innovative binary, ternary or even quaternary blends of cements will go a long way in obtaining the end results. In this context, it is obvious that the standard specification of blended and composite cements need to be revisited to minimize the hindrances for using lower and lower amounts of clinker and to maximize the efforts to move towards performance specification in place of prescriptive ones. Blended Cements for Concrete Durability and Environmental Sustainabilty One of the most influential factors for durability of reinforced concrete is the number, size and continuity of voids through which CO and 2 - Cl migrate. Voids are classified by size. Capillary pores, ranging from 10µm to several microns, are strongly correlated to the strength and durability of concrete. Production of strong and durable concrete is dependent primarily on minimizing its void structure and eliminating the interconnectivity of pores and voids. In this context, the blended cements become extremely relevant. From the basic principles of materials science it is evident that, the denser the development of microstructure created by the cement hydration products, the lower are the shrinkage and Table 4. Impact of SCMs on CO emissions per cubic meter of concrete 2 Cementitious material per m 3 % SCM CO 2 per m 3 335 0 25 50 312 240 167 280 0 25 50 262 208 139 220 0 25 50 212 161 113 23