Cement: powder hydraulic inorganic cementing material. Mud can be hardened in air after being mixed with water, and the hardening effect is better in water, and materials such as sand and stone can be firmly bonded together. The word "cement" is developed from the Latin caementum, which means crushed stone and flaky.

The mixture of early lime and pozzolan is very similar to modern lime-pozzolan cement. After hardening, the concrete made of crushed stone not only has high strength, but also can resist the erosion of fresh water or salt water. For a long time, as an important cementing material, it has been widely used in civil engineering, water conservancy, national defense and other projects.