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Binding agent of present-day concrete. It is a finely ground powder made by burning and grinding a limestone mixed with clay or shale. Its inventor, Joseph Aspdin (1799–1855), patented the process in 1824, naming the material for its resemblance to the limestone of the Isle of Portland, England. The cement combines chemically with the water it is mixed with, then hardens and strengthens.
This entry comes from Encyclopædia Britannica Concise. For the full entry on portland cement, visit Britannica.com.