function of admixture in concrete

The function of admixtures is to modify some or all of the properties of fresh concrete or hardened concrete. This modification can be achieved by adding one or more specific chemical compounds with a special chemical action and a formulated chemical composition to the concrete mix before or during its mixing, transporting, placing, compacting or curing.

Rate of Hydration & Setting Time

The initial rate of hydration and setting time in concrete is affected by a number of factors such as temperature, relative humidity, ambient air pressure and pore size distribution among others. For this reason, a variety of admixtures are available to control the initial rate of hydration and setting time.

Anti-Freeze & Gas-Forming Agents

A number of admixtures are used to help prevent the formation of gas in concrete, thereby increasing its durability. These include aluminium powder, zinc and magnesium powders and hydrogen peroxide.

Water Reducers & Retarders

Admixtures are also used to help increase the flowability of concrete, mortar or grout without lowering its strength by reducing its water content. This is done by adding water reducers such as Type F or G admixtures to the concrete mixture, which can be reduced by a specified percentage of the cement.

Superplasticizers & Plasticisers

Admixtures are useful in producing concrete which is strong, durable and economical. They also improve the workability of fresh concrete and increase its resistance to freeze-thaw damage. They are usually added to the concrete mix during its mixing, transporting and placing process.