what is portland cement

Portland Cement is a finely pulverized material consisting principally of compounds of lime, silica, alumina, and iron. It is manufactured from selected materials under closely controlled processes . The process starts by mixing lime-stone or marl with such other ingredients as clay, shale, or blast furnace slag in proper proportions and then burning this mixture in a rotary kiln at a temperature of approximately 2700ºF(1482ºC)to fuse it into clinker(rocklike shapes of varying size averaging ¾ in. [19mm] in diameter ). The clinker is cooled and then pulverized together with a small amount of gypsum, which slows the setting time. The finished product, Portland cement, is so fine that nearly all of it will pass through a sieve with 40,000 openings to the square inch (62 openings per mm²).

When Portland cement is mixed with water, a paste is formed which first sets(become stiff) and then hardens into a solid mass. The setting an hardening (hydration) are brought about by chemical reactions between the Portland cement and water. The reaction is not simply one of evaporation or drying.