4.1 : 混凝土

Concrete is a commonly used structural material in the construction of buildings, bridges, airfields, highways, dams, and silos.

Concrete is produced by mixing specific proportions of cementitious materials like cement, fine aggregates like sand, and coarse aggregates like gravel with water. Sometimes, admixture is also mixed to modify the characteristics of the resulting concrete.

In a fresh concrete matrix, the voids of bigger aggregates are filled by smaller aggregates, and the remaining voids are filled with cement-water paste, forming a coating over the aggregates.

This mix hardens with time to a rock-like mass, which is strong in compression and weak in tension. As a result, reinforcements may be introduced to strengthen the concrete.

Material selection, mixing, transporting, placing, compacting, and curing govern concrete's performance.

Fresh concrete should be workable, and when placed, the ingredients should not segregate or bleed water.

Generally, concrete is produced as ready-mix concrete, pre-cast concrete sections, and concrete masonry units.