How is concrete made?

Question

How was concrete discovered

Answer 1

Cement is a logical progression from other lime based materials which are fired to prepare them to take up water again, where they produce a solid substance. Romans used a lot of concrete and recent claims are that the tops of some pyramids are concrete, not blocks of stone moved up there.
Concrete is cement, sand, and various sized stones (gravel). The cement does the chemistry holding it together and the sand and gravel provide the wear surface, provide structure and reduce the amount and therefore the cost of cement which is relatively costly compared to sand and stone.

Answer 2

Concrete was made by the Romans, and in fact some concrete structures dating from that time are still standing. Concrete is a mixture of sand, aggregate (rock of various sizes), water, and cement powder; the mixture is a slurry when installed, but the cement absorbs water to form a hydrated compound which interlocks with the other solid consitituents to make a solid mass.