Cement, Energy and Environment

5 Apart from the principle of particle packing, the addition of multiple SCMs in some cases turn out to be very effective, if the materials added have certain synergy in their reactivity. This is seen in the case of Portland limestone calcined clay cement (more popularly known as LC 3 cement). In this composite cement the limestone component becomes partially reactive during hydration and a mono-carbo-aluminate hydrate phase is formed, imparting better properties in mortar and concrete. In fact, this cement has higher early age strength in mortar than the Portland calcined clay cement and it displays high chloride resistance in concrete, compared to other blended cements. It is pertinent to mention here that India has embarked on production of MPCC with the adoption of IS-16415:2015 with the following formulation:  Clinker/OPC (IS-16353): 35-65%  Fly ash (IS-3812 Pt I): 15-35%  Granulated slag (IS-12089): 20-50%. The product may be obtained by co-grinding the ingredients or by blending the fine powders of the ingredients to pass 300 Blaine surface. It is obvious that our national specification is very limited in scope and does not take into consideration the basic concepts discussed earlier. In order to derive the real advantage of MPCC, the national standard specification needs to be appropriately revised in due course. At the same time, it must be understood that MPCC is an important route in achieving lower clinker factor as shown in Fig.8. MORE CONCRETE WITH LESS CEMENT In order to produce more concrete with less cement there are several avenues known and practised. In the present context, however, two specific technological approaches may be mentioned: one, high-volume fly ash concrete and another, concrete containing fillers. The high-volume fly ash concrete with more than 50% cement replacement is a widely tried and well proven technology in Canada and the United States. Successful trials were carried out in India for making concrete pavements several years back but its wider adoption has not taken place even now. It is certainly time to relook into this technology and overcome the barriers of implementation. Fig. 8. Steps towards reducing the clinker factor As already mentioned, the other global development is the use of fillers in concrete. Fillers, as we all know, are particulate materials, inert or mildly reactive, produced by grinding to replace clinker or other reactive SCMs. Granite and sandstone, co-ground with cement, were first used in a dam built by the US Bureau of Reclamation between 1912 and 1916. It appears that the concept is coming back to the industry almost after 50 years in the form of fine ground limestone and dolomite. The grinding technology developers are engaged in developing the process of preparing fillers for the binder industry by using special dispersants. Globally an increasing trend is observed in the use of limestone fillers as shown in Fig.9. Morocco, Thailand, some of the African countries and China are demonstrating visibly increasing trend. It has been reported that the national standard of Ghana has approved the use of dolomite powder in cement. It is known that EU countries are producing Portland limestone cement with about 18-20% limestone powder. The filler technology is very important for the reduction of clinker factor and the developments need to be closely pursued. Step 1 • Normal Portland Cement with 5% Filler & 5% Gypsum • About 90% Clinker in Cement Step 2 •Blended Portland Cement with Single Blending Material •About 55-70% Clinker (Except PSC with Cl 35-45%) Step 3 •Portland Cement with Multiple Blending Materials •About 45-50% Clinker in Cement