3.3. Reinforced concrete wall
Concrete is manufactured from aggregates (rock and sand),hydraulic cement and water. It usually contains a small amount of chemical admixture, and often has a mineral admixture that replaces a portion of the cement. A typical concrete formulation contains a large quantity of coarse and fine aggregates, a moderate amount of cement and water, and a small percentage of admixture.Most of these constituents are themselves manufactured products,by-products, or materials extracted by mining. In order to assess the environmental impact of concrete manufacture, it is necessary to consider the impact of each separate constituent. The constituent with the highest environmental impact is cement. Portland cement is usually manufactured by heating a mixture of limestone and shale in a kiln to a high temperature (approximately 1500◦C), then inter grading the resulting clinker with gypsum to form a fine powder. Thus, it is not surprising that the embodied energy in Portland cement is high. The average value of the energy required to make cement stands at about 5.85 MJ/kg. The energy required for concrete manufacture, considering all constituents, yields an average energy expenditure of 1.4 MJ/kg [47]. Reinforced concrete is made with steel rods, and the energy consumed in the steel production is 42 MJ/kg [47].