ABSTRACT
Portland-based cements are the most common inorganic binders used in concrete manufacturing. According to the European Cement Association, world cement production in 2014 was estimated as 4.3 billion tons (CEMBUREAU, 2015). When compared with figures at the turn of twentieth century, there appears to be more than 130% increase in cement production which indicates that portland-based cements will continue to be key construction materials in the foreseeable future. On the other hand, the cement industry is confronted with serious energy and emissions problems. Cement manufacturing accounts for approximately 75% of total energy use in non-metallic minerals production and about 25% of total industrial CO2 emissions (IEA, 2007). These values correspond to about 2% and 5% of total global and total industrial energy consumption, respectively (Placet and Fowler, 2002). Energy represents about 30% of the total cost of cement and the main energy consuming process in cement manufacturing is the burning process in the rotary kiln. A typical modern rotary kiln consumes 3.1 GJ/ton of clinker produced. The value may be as high as 6.5 GJ/ton in less efficient kilns and for wet raw materials. The world average is reported as 3.8 GJ/ton. Besides, total electrical energy consumption is stated to be around 0.38 GJ/ton. Carbon dioxide (CO2) emission due to carbon-based fuels is approximately 0.3 kg/kg of clinker in a modern rotary kiln and may increase up to 0.6 kg/kg of clinker in less efficient kilns. Besides the fuel derived CO2, about 0.57 kg/kg of clinker CO2 is given off through the calcination of raw materials, basically limestone (Gartner, 2004; CSI, 2005; Damtoft et al., 2008). Therefore, there has been a continuous effort in increasing the energy efficiency and decreasing CO2 emissions in cement manufacturing. In fact, many improvements in process efficiency have been achieved by the cement industry. However, emissions are continuing to increase globally due to the increase in population and growing industrialisation especially in developing countries (Imbabi et al., 2012).
