What types of admixtures are used in concrete?

Five Functions. Admixtures are classed according to function. There are five distinct classes of chemical admixtures: air-entraining, water-reducing, retarding, accelerating, and plasticizers (superplasticizers).

What is admixture concrete?

An admixture is defined as “a material other than water, aggregates, cementitious materials, and fiber reinforcement, used as an ingredient of a cementitious mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing” (ACI Committee 212, 2010).

What are the examples of admixtures?

There are two types of admixtures, viz., chemical admixtures and mineral admixtures. Accelerators, Retarders, Water-reducing agents, Super plasticizers, Air entraining agents etc. are the commonly used chemical admixtures. Fly-ash Blast-furnace slag, Silica fume and Rice husk Ash are the examples of mineral admixtures.

What are the different types of chemical admixtures?

Chemical admixtures can be divided into five types: accelerating, retarding, water reducing/plasticizing, air entraining, and waterproofers. Chemical admixtures should be used judiciously because the addition of wrong quantities can affect the long-term performance of concrete in many ways.

What are the functions of admixtures?

Functions of Admixture

• To improve workability of fresh concrete.
• To improve durability by entrainment of air.
• To reduce the water required.
• To accelerate setting & hardening & thus to produce high early strength.
• To aid curing.
• To impart water repellent / water proofing property.

Why accelerators type of admixture are used in concreting?

A cement accelerator is an admixture for the use in concrete, mortar, rendering or screeds. The addition of an accelerator speeds the setting time and thus cure time starts earlier. This allows concrete to be placed in winter with reduced risk of frost damage.

What is concrete chemicals Name some concrete chemicals?

There are several chemical admixtures that include water reducers, accelerators, anti-freezing admixtures, air-entraining admixtures, alkali-aggregate inhibitors, shrinkage compensating admixture, and corrosion inhibitors etc. Figure 1 shows some of the chemical admixtures meant for use in cement concrete.

Where accelerating admixtures are commonly used?

Accelerating admixtures can be used to increase either the rate of stiffening or setting of the concrete or the rate of hardening and early strength gain to allow earlier formwork striking and demoulding. Most accelerators achieve one rather than both of these functions.

Why are retarders and accelerators admixtures used in concrete?

Retarders keep concrete workable during placement and delay the initial set of concrete. Chloride Free and Accelerating Compund for Concrete and Mortar. Accelerator is use for reduce setting time. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.

What is the ratio of water to cement?

Water to Cement ratio. The most important factor determining the strength of concrete is the water to cement ratio. It is the ratio of weight of mixing water (free water available for the reaction with cement) to that of cement in the mixture. Cement needs water of about 38\% by weight for complete hydration.

What is the mixing ratio for cement?

A concrete mixture ratio of 1 part cement, 3 parts sand, and 3 parts aggregate will produce a concrete mix of approximately 3000 psi. Mixing water with the cement, sand, and stone will form a paste that will bind the materials together until the mix hardens.

What are the mix ratios for cement and sand?

The basic mix ratio for concrete is one part water, two parts cement and three parts sand. An alternative ratio is one part cement, two parts sand and three parts gravel with enough water added until the mixtures reaches the consistency of thick mud.

What are concrete additives?

Concrete additives are added to the mixture of water cement and aggregate in small quantities to increase the durability of the concrete, to fix concrete behavior and to control setting or hardening. They can either be liquid or powdered additives.