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Top1. Introduction
Concrete is a basic building material that will continue to be in demand far into the future. A world without concrete, and its dominant precursor, Ordinary Portland Cement (OPC), is hard to imagine. Although there are different types of concrete that have been developed for use in different applications, their common virtues are familiarity, versatility, strength, durability, wide availability, fire resistance, resistance to the elements and comparatively low cost. Global concrete industry uses approximately 1.6 billion tonnes of cement and 10 billion tonnes of sand, gravel, and crushed rock every year (Mehta, 2001). The world's yearly cement production of 1.6 billion tonnes accounts for about 7% of the global loading of carbon dioxide (CO2) into the atmosphere (Mehta, 2001).There are two major sources of GHG emissions associated with concrete production: (a) The mining, processing, and transport operations involving large quantities of aggregate consume considerable amounts of energy, produce large quantities of GHGs, and adversely affect the ecology of the areas they are extracted from. As the hauling distances between the quarries to the processing plants and processing plants to construction sites increase, GHG emissions associated with the transportation of NA also increase. (b) The manufacturing of cement involves emission of considerable amount of GHG in the atmosphere. It is estimated that producing one tonne of Portland cement requires about four giga-joules of energy, which in turn emits 1.25 tonnes of carbon dioxide into atmosphere (Wilson, 1993).