Chemical concrete admixtures are material in the form of powder or fluids that are added to concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement and are added to the the concrete at the time of batching/mixing. The most common types of concrete admixtures are:
1. Accelerators speed up the hydration (hardening) of the concrete.
2. Retarders slow the hydration (hardening) of the concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable.
3. Air-entrainers add and distribute tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles thereby increase the concrete’s durability.
4. Plasticizers (water-reducing admixtures) increase the workability of plastic of fresh concrete, allowing it be placed more easily with less consolidating effort.
5. Superplasticizers ( high-range water-reducing admixtures)are a class of plasticizers which have fewer deleterious effects when use to significantly increase workability. Alternatively; plasicizers can be used to reduce the water content of a concrete (and have been called water reducer due to this application) while maintaining workability. This improves its strength and durability characteristics.
6. Pigments can be used to change the color of concrete, for aesthetics. Mainly they are ferrous oxides.
7. Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.
8. Bonding agent are used to create a bond between old and new concrete.
9. Pumping aids improve pumpability, thicken the paste and reduce dewatering of the paste.
Thus, chemical admixture is one ingredient creating concrete that provide the differentiation of concrete types.