Types of Concrete Admixture

concrete admixture is any material added to the cement-particle system to modify the properties or performance of concrete. Admixtures may be used before or during the pouring of concrete to achieve desired outcomes.

Admixtures come in several categories:

Retarding and Accelerating Adminxtures
Retarding admixtures delay the setting time of concrete by adding sugars, carbohydrate derivatives, soluble zinc salts, borates, calcium sulfate, starch, ferrous and ferric chloride, lignosulphonate acids, etc. A 0.05% concentration of retarding admixture delays the setting time of concrete by about 4 hours.

Accelerating admixtures improve the set of concrete by increasing its rate of early strength development. This allows the concrete to be poured earlier and ensures that it will have sufficient strength to resist freezing before it is exposed to weather and deicing chemicals.

Air-Entraining Adminxtures

Air-entraining admixtures encourage microscopic air bubbles to form and stabilize during the mixing process, which significantly increases the durability of concrete. These bubbles also increase its freeze-thaw resistance by providing unsaturated void spaces.

Mid-range Water Reducing admixtures/Plasticizers

A 5% concentration of a mid-range water-reducing admixture by weight of cement will decrease the water-cement ratio in concrete by up to 20%, which will increase the compressive strength of concrete by approximately 30%. This admixture can be added during batching or at the job site.

Flash-setting admixtures

A 2.5% 4% concentration of flash-setting admixture will make the initial setting of concrete occur within 3 minutes and final setting within 7 10 min. This admixture will also enhance the initial and ultimate compressive strength of concrete, but will decrease it by 20% 30% after 28 days.