Different types of concrete additives are added to a mixture of cement, aggregate and water either in the plant or on site to alter the properties of the hardened concrete. These admixtures lower construction costs and alter the quality of the newly poured concrete.
Water reducing – Plasticising and superplasticisers
Admixtures that reduce the amount of production water, such as ligno-sulphonates and hydrocarbolic acid salts, belong to this category. They can also reduce segregation, improve flowability and permeability of the mix, and enhance the rheological properties.
Pozzolan admixture (Volcanic ash admixture)
A mineral admixture that affects the properties of hardened concrete through hydraulic action or pozzolanic action. It can be used to prepare dense concrete mixes suitable for dams, reservoirs and other water-retaining structures.
Antifreeze – Lowers freezing point of water to set and harden concrete at negative temperatures in winter.
Superplasticisers – Reduces the amount of water required to produce high strength and performance concrete.
Accelerating – Speeds up the rate of stiffening, setting and hardening of concrete to enable formwork striking or demoulding earlier.
Air entraining – Introduces air bubbles into concrete by chemical reaction to adjust the apparent density and improve freeze-thaw resistance.
These admixtures are effective in preventing the formation of cracks during cold weather by relieving internal pressure that forms at low temperatures.
Silica dust and silica fly ash are widely used in concrete for their unique properties.
They are a popular concrete additive because they can lower the heat of hydration of concrete, make it more durable and less absorbent. They are also very useful for preparing watertight concrete.