About cement and concrete

Cement comes from the Latin word caementum, meaning “rough-cut stone."
Concrete is a combination of the Latin prefix com-, “together,” and crescere, “to grow.”

Is concrete the same thing as cement?
Not at all! Cement is a powdered mineral substance, and concrete is a solid block. Concrete is made when cement and water are mixed together with sand and crushed rock. When the cement meets the water, a chemical reaction takes place and it acts like a glue, binding everything together into a hard block of concrete.

What is cement?
Cement is the key ingredient in concrete, the binding agent that holds everything together. Modern cement is made from mixtures of naturally occurring minerals that contain calcium oxide (usually from limestone) and silicon dioxide (usually from clay). The minerals are heated to extremely high temperatures (1450°C), which chemically transforms them into hard marble-like nodules called clinker. The clinker is then ground into an extremely fine powder. There are more than 200 billion grains of cement powder in a kilo of cement! When cement is mixed with water, it forms very strong bonds with sand and other aggregates, bringing the whole mixture together into a rock-solid mass.

What is concrete?
Concrete is a composite material: a mixture of cement, water, an "aggregate" – sand or gravel -- and sometimes ingredients called admixtures. Thanks to the special binding properties of cement, concrete is a very resilient, durable material that can bear heavy loads and resist environmental extremes. The time it takes for concrete to go from a pourable substance to a surface that you can walk on depends on the kind of cement used and how much water is added to the mix, as well as factors like outside temperature and humidity. But for typical applications, concrete will stay pourable for 1-3 hours and can be walked on after a day. A standard strength test is taken at 28 days, even though the concrete continues to slowly harden over many years.