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Raw Material Preparation The raw materials used in the manufacture of cement are limestone, shale, sand and iron ore, typical chemical compositions of which are given in the table below. Limestone makes up approximately 80% of the raw material requirements, composes of mainly calcium carbonate with small intrusions of magnesium carbonate. Quarrying operations are geared to minimizing the intrusions. The limestone is crushed to less than 25mm in size. MgO in the cement, if present in sufficient quantities will cause expansion upon hydration thus resulting in unsoundness in the concrete.  Due to the variable nature of these components, they are pre-blended prior to their use. It is crushed and stored in a pre-blending hall, utilizing the chevron pile stacking method. In this method, stacking takes place at one end of the pile. At the other end of the pile the material is reclaimed and then stored in a feeding hopper which is ready for use. Raw Material Proportioning & Grinding The raw materials are extracted from the hoppers via weigh-feeders. The materials are conveyed to the grinding mill and are ground to a suitable fineness, called raw meal at this stage. This is then stored in a blending silo and blended to ensure homogeneity. The proportions of the 4 components are controlled by the continuous sampling and testing of this raw meal. The raw meal chemical composition is determined by the use of an x-ray fluorescence analyzer. This is linked to the computer which will automatically adjust the weigh-feeders, so that the resultant raw meal stored in the blending silo meets the preset parameters. After blending this material is then discharged into the storage silos ready for the next phase of production. The parameters used in the control of the raw meal are lime saturation factor, silica modulus and iron modulus. These are actually proportions of the various chemical components which are desired in the resultant clinker.  As coal is used as a fuel the coal ash, a combustion product of the coal, has to be treated as an individual raw material component and the appropriate corrections made at the weigh-feeder stage. 
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