Concrete is a construction admixture that consists of cement (commonly Portland cement), aggregate (generally gravel plus sand) and water.
Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material. It is used to make pavements, architectural structures, foundations, motorways/roads, overpasses, parking structures, brick/block walls and footings for gates, fences and poles. from wikipedia
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