Types of Concrete Admixtures

Admixtures are used in almost any concrete mixture produced today. Following is a list of the most common ones:

Accelerators

When you need fast strength gain because other components require construction adjacent to the concrete. Accelerating admixtures shorten the setting and early-strength development time. They consist of Calcium chloride, Triethanolamine, sodium thiocyanate, calcium formate, calcium nitrite, and calcium nitrate. They are governed by ASTM C494, ASTM D98, AASHTO M194 and AASHTO M144.

Air Entraining Admixtures

Air entraining admixtures:

• Improve durability in freeze-thaw environments.
• Increase resistance to de-icer chemicals.
• Increase durability in sulfate and alkali-reactive environments (i.e. exposed to ground).
• Improve workability.

They consist of salts of wood resins (Vinsol resin), some synthetic detergents, salts of sulfonated lignin, salts of petroleum acids, salts of proteinaceous material, fatty and resinous acids and their salts, alkylbenzene sulfonates, and salts of sulfonated hydrocarbons.

Alkali-Aggregate Reactivity Inhibitors

These admixtures reduce expansion related to alkali-aggregate reactivity, which are generally a problem when concrete is in permanent contact with soil. They consist of barium salts, lithium nitrate, lithium carbonate, and lithium hydroxide.

Coloring Admixtures

These admixtures produce colored concrete. They are governed by ASTM C979 and consist of carbon black, iron oxide, phthalocyanin, umber, chromium oxide, titanium oxide, and cobalt blue.

Corrosion Inhibitors

Corrosion inhibiting admixtures reduce steel corrosion activity in a chloride-laden environment. They are governed by ASTM C1582. They consist of calcium nitrite, sodium nitrite, sodium bezoate, certain phosphates or fluosilicates, fluoaluminates, and ester amines.

Retarding Admixtures

These admixtures reduce concrete setting time. They are governed by ASTM C494 and AASHTO M194. They consist of Lignin, Borax, sugars or tartaric acid and salts.

Shrinkage Reducing Admixtures

When you need to place other concrete or materials adjacent to the concrete and need to prevent drying shrinkage, this admixture is for you. It consists of Polyoxyalkylene alkyl ether or propylene glycol.

Superplasticizers

The opposite of retarding admixtures, these increase flowability of concrete and reduce water-cement ratio requirements. They are governed by ASTM C1017 and consist of sulfonated melamine formaldehyde condensates, sulfonated naphthalene formaldehyde condensate, lignosulfonates, or polycarboxylates.

Water Reducing Admixtures

This admixture allows you to reduce the water content without affecting the other strength properties. They are governed by ASTM C494 and AASHTO M194, and consists of lignosulfates, hydroxylated carboxylic acids, and carbohydrates.