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Pyroprocessing is an important stage in cement manufacturing. In this process, materials are subjected to high temperatures so as to cause a chemical or physical change. Its control improves efficiency in energy utilization and hence enhances production for good quality assurance. Kilns used in cement manufacturing are complex in nature. They have longer time constants, and raw materials used have variable properties. They are therefore difficult to control. Additionally, the inclusion of various alternative fuels in burning makes the process more complex as the fuel characteristics remain inconsistent throughout the kiln operation. Fuel intensity standards for kilns using fuel oil are very high, ranging from 2.9 GJ to 7.5 GJ/ton of clinker produced. Grinding of clinker consumes power in the range of 2.5 kWh/ton of clinker produced. These and other pyroprocessing parameters make cement production costly. The pyroprocessing process in kilns and the grinding technologies therefore have to be optimized for best processing. This paper discusses the cement manufacturing and grinding processes. The traditional kiln technologies and the current and emerging technologies together with general fuel and energy requirements of cement manufacturing have been discussed. From the discussion, it has been established that the cement manufacturing and grinding technologies are capital-intensive investments. The kiln processes are advanced and use both electricity and natural fuels which are expensive and limited factors of production. The raw materials used in cement manufacturing are also limited and sometimes rare. The calcination of the raw materials requires external energy input which has contributed to the high cost of cement especially to low-income population in the developing countries. Self-calcining materials, in which the pozzolanic materials burn on their own, are potential pozzolanic materials with great potential to lower the cost of cement production. Such materials, as shown from the previous research study, are rice husks, broken bricks, spent bleaching earth, and lime sludge. There is a need, therefore, for research to look into ways of making cement using kiln processes that would use this property. This will be cost-effective if successful. It can be done at micro- and small-scale enterprise.

Blended cements are preferred to Ordinary Portland Cement (OPC) in construction industry due to costs and technological and environmental benefits associated with them. Prevalence of significant quantities of carbon dioxide (CO2) in the atmosphere due to increased industrial emission is deleterious to hydrated cement materials due to carbonation. Recent research has shown that blended cements are more susceptible to degradation due to carbonation than OPC. The ingress of CO2 within the porous mortar matrix is a diffusion controlled process. Subsequent chemical reaction between CO2 and cement hydration products (mostly calcium hydroxide [CH] and calcium silicate hydrate [CSH]) results in degradation of cement based materials. CH offers the buffering capacity against carbonation in hydrated cements. Partial substitution of OPC with pozzolanic materials however decreases the amount of CH in hydrated blended cements. Therefore, low amounts of CH in hydrated blended cements make them more susceptible to degradation as a result of carbonation compared to OPC. The magnitude of carbonation affects the service life of cement based structures significantly. It is therefore apparent that sufficient attention is given to carbonation process in order to ensure resilient cementitious structures. In this paper, an indepth review of the recent advances on carbonation process, factors affecting carbonation resistance, and the effects of carbonation on hardened cement materials have been discussed. In conclusion, carbonation process is influenced by internal and external factors, and it has also been found to have both beneficial and deleterious effects on hardened cement matrix.