Cement manufacture involves the production of hydraulic cements, primarily Portland cement, which is composed mainly of hydraulic calcium silicates. The process starts with the extraction of raw materials, predominantly limestone and clay, which are then crushed, blended, and heated to approximately 1450 °C in a rotary kiln. This process, known as calcination, leads to the formation of clinker, which is then finely ground together with gypsum to produce cement. The chemical reactions during calcination release carbon dioxide, primarily from the decomposition of limestone and the combustion of fuels, making cement production a significant contributor to global CO 2 emissions.