Concrete, from the Latin word concretus, meaning having grown together, almost always consists of a relatively unreactive filler, or aggregate; Portland cement (from the Latin caementum, meaning quarry stone; water; and voids. The filler is usually a conglomerate of rocks and sand, and more specifically, of gravel, pebbles, sand, broken stone, and blast-furnace stony matter known as slag.

Portland cement is made up of finely pulverized stony matter produced by heating mixtures of lime, silica, alumina, and iron oxide in air to about 2,642°F (1,450°C). The properties of the cement may be varied by changing the relative proportions of the ingredients, and by grinding to different degrees of fineness. Chemically, Portland cement is a mixture of calcium aluminum silicates, typically including tricalcium silicate (3CaOSiO₂), dicalcium silicate (2CaOSiO₂), and tricalcium aluminate (3CaOAl₂O₃); it may also contain tetracalcium aluminoferrate (4CaOAl₂O₂ Fe₂O...