Cement is a fine, gray powder that is used as a construction binding material. When mixed with water, cement reacts chemically and becomes hard and strong. Cement is categorized as either hydraulic or nonhydraulic, depending on how it mixes with water.
Nonhydraulic cement does not harden underwater or in damp conditions. Certain chemicals are added to make hydraulic cement, which sets underwater or in wet conditions.
Cement is made by combining silicon, aluminum, iron, calcium and other chemicals in a controlled mixture. Other materials added to the mixture include chalk, clay, slate and limestone. When combined, the ingredients form a hard substance that is ground into cement.
Cement is also known as Portland cement. It was invented by Englishman Joseph Aspdin in 1824 and was named for its similarity to limestone from the Isle of Portland. The word cement originated in the time of the Romans, whose term opus caementicium referred to masonry similar to modern concrete.
Portland cement is the main ingredient in concrete, which is made by adding rock, sand and water to form a paste that hardens. Concrete is made stronger by adding more cement and is weakened by adding more water. Concrete is used in most buildings, bridges and tunnels due to its strength. Moisture and pests do not weaken it, and it can withstand most natural disasters, including earthquakes and hurricanes.