Concrete vs. Cement: Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone. The paste is water and Portland cement, a chemical combination mixed with limestone, shells, chalk, shale, clay and other materials. Through a process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years, meaning that concrete gets stronger as it gets older.
