Concrete

Definition

A general name used to refer to manufactured or synthetic rock material that is formed by cohesion and then solidifies. Concrete has similarities to a natural deposit of well-cemented, clastic, sedimentary rock called conglomerate. Typical concrete constituents are cement, water, mineral aggregates, and chemical admixtures. Bituminous material is the cement in asphalt concrete, typically called “asphalt” or “black top”; however, the most common cement used in what is called “concrete” is Portland cement, a compound made from clay and limestone. Clay is a source of silica, alumina, and iron, which upon wetting will react with calcium oxide derived from high-temperature roasting of crushed and powdered nearly pure calcite limestone (CaCO₃). Wetting transforms powdered Portland cement by hydration into a durable strong solid composed of four silica and alumina compounds: tricalcium silicate (3(CaO)∙SiO₂), dicalcium silicate (2(CaO)∙SiO₂), tricalcium aluminate (3(CaO)∙Al₂O₃),...