Cement, Energy and Environment

serious problem in this specific trial. With no gainful results obtained with only raising the lime content in clinker, the options left were to grind the blended cements to specific surface levels beyond 500 2 m /kg or to produce mineralized clinker, instead of the normal high-lime clinker. Both these options were found to be fairly expensive. In fact, both these measures demand a careful viability study before implementation and, for brevity, are not discussed further in this article. Performance Specifications and Ternary-Blend Cements The product technology that is considered highly potential to bring down the CO emissions 2 is the manufacture of blended cements, incorporating not one but two or more SCMs. The success of this technology, however, relies more on adopting 'performance specifications', rather than the existing 'prescriptive specifications'. The present PSC and PPC specifications are prescriptive, meaning that these standards are based on measured chemical and physical properties that are assumed to be related to the performance of the cement in concrete. Based on the same prescriptive principles, the 'Composite Cement - Specification' (IS: 16415:2015) has been introduced, which permits the simultaneous use of GGBS (20-50%) and fly ash (15-35%) with Portland cement or clinker (35-65%). It is expected that this specification may help reduce further the clinker factor in cement, thereby decreasing the CO 2 emissions. The current specification of composite cement has the restriction of using only the above two SCMs and the stipulation of complying with the chemical and physical properties of the cement, and not the actual performance in concrete. The absence of the performance standard has now led to limiting the use of composite cement to PCC only in our country. The mandated restriction of using composite cement in RCC is a practical barrier to promoting the composite cement and realizing the benefit of reduced CO emissions. 2 It is important to note that internationally the trend is more towards the performance specification. For example, ASTM C 1157, performance specification for hydraulic cement, simply requires that the hydraulic cement meet certain physical performance test requirements, thus focusing on material performance and not material composition. The approach promotes unrestricted innovative development of composite Portland cements. Six hydraulic cement types are available under ASTM C1157: § GU (general use) § LH (low heat of hydration) § MH (moderate heat of hydration) § HE (high early strength) § MS (moderate sulfate resistance) § HS (high sulfate resistance) In the United States, under the umbrella of ASTM C 1157 cements such as the Portland Limestone Cement (PLC) and high-volume Activated Class C fly ash based cement (proprietary) are in the market. Many other innovative products are being developed for commercial use. Compared to such developments, the Indian scenario is extremely conservative. Products like Portland Limestone Cement (PLC) or Limetone Calcined Clay cement (Lc3), which are ready for commercial applications, are still being discussed and debated in our country. It would not be too judgemental to say that the role to be played by the blended cements in reducing the CO emissions is not being 2 expanded and implemented at a pace that India needs today. Table 4 summarizes illustratively the impact of the addition of SCMs to concrete 22