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