Concrete

Concrete is a material commonly used in construction. It is composed of cement, aggregate, water and special chemicals known as admixtures.

## Cement[edit]

Usually, Portland cement is used to make concrete. Portland cement contains calcium silicates.

## Admixtures[edit]

Admixtures change the properties of the concrete. Different admixtures are used depending on the requirements:

* Accelerators make the concrete harden faster.
* Pigments change the colour of the concrete.
* Bonding agents create a good bond when adding new concrete to old.

## Reinforced concrete[edit]

Concrete is very strong in compression, but weak in tension. To make it a more useful construction material, steel bars (rebar) are often installed in fresh concrete, to increase the tensile strength.