Portland Cement

Portland cement is a hydraulic binder made by firing limestone and clay together at high temperature and grinding the resulting clinker with a small proportion of gypsum, the essential ingredient that, mixed with water, sand and aggregate, produces modern concrete. Patented in England in 1824 by Joseph Aspdin, who named it for its resemblance to Portland stone, it largely displaced the older, less reliable lime-based mortars and cements over the nineteenth century and underlies essentially all modern concrete construction, from plain unreinforced footings to the reinforced and prestressed structural concrete that transformed twentieth-century building.