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Admixture in Concrete: Meaning, Functions and Types

Admixture in concreteAdmixture in concrete

Worker man house builder mix mortar from a trough in bucket

Concrete is a widely used construction material. Its four main ingredients include cement, water, sand and aggregates. The cement and water form a paste that binds the sand and aggregates, and the result is a strong and hard structure that can support buildings of all shapes and sizes. Another ingredient, known as admixture, may be added to improve certain properties of concrete. You can find information on what admixture in concrete is, its uses and types.

What is an Admixture?

An admixture is a constituent of concrete or mortar to modify one or more properties of the concrete in its plastic or hardened state. It is typically added to the concrete batch before or during its mixing.

What are the Uses of Admixtures?

Admixtures are widely used in the following circumstances:

How Admixtures Impact Fresh Concrete’s Properties

Admixtures have the following effects on freshly mixed concrete:

How Admixtures Impact Hardened Concrete’s Properties

When the concrete is hardened, admixtures lend the following:

Types of Chemical Admixtures

Per Indian Standard (IS) code 9103, admixtures are of the following types:

Accelerating Admixtures

Accelerating admixtures are added to concrete, mortar or grout to increase the rate of cement hydration, reduce the setting time and accelerate the hardening of concrete. This type of admixture reacts with the tri-calcium silicate component of the cement, increasing the reaction time between cement and water. Accelerating admixture helps the concrete to cure faster and in a uniform manner.

Retarding Admixtures

A retarding admixture delays the setting time of cement paste. It decreases the initial reaction rate between cement and water, consequently reducing the concrete’s setting time. The admixture coats the surface of the tri-calcium silicate components. This is beneficial when concrete needs to be transported for long distances before being placed.

Water-Reducing Admixtures

Also known as a plasticiser, this type of admixture performs two types of functions. It can either increase freshly mixed concrete’s workability without the need for additional water or maintain workability with less water. This makes the concrete more workable without compromising its compressive strength. Water-reducing admixtures can also reduce the quantity of cement required, leading to economical projects.

Superplasticising Admixtures

Superplasticisers impart high workability to concrete or allow a substantial reduction of water content for a given workability. Typical water-reducing admixtures can reduce the water requirement by 10 to 15%. However, superplasticisers can reduce the water content required by about 30%. Based on their chemical composition, superplasticisers are divided into four main categories – sulphonated melamine formaldehyde condensates, sulphonated naphthalene formaldehyde condensates, modified lignosulphonates and other sulphonic acid esters and carbohydrate esters.

Air Entraining Admixtures

Air-entraining admixtures cause air to be incorporated in the form of tiny bubbles in the concrete or mortar to increase resistance to freezing and thawing conditions. Entrained air can break the continuity of capillaries, restricting the water flow between cement particles. The bubbles act as a fine filler and increase the total surface area of the constituents relative to the water volume.

Whether you want water-resistant cement for your next pool project or Portland Pozzolana Cement (PPC) for all other housing construction projects, JK Cement has you covered.

FAQs

What is the difference between admixture and additives?

Admixture is an additional ingredient of concrete. Additives are chemical substances added to the cement at the time of manufacturing.

Can admixtures make concrete water-resistant?

A special type of admixture known as water-resistant admixture, permeability reducing admixture, etc., can make the concrete water resistant.

What are mineral admixtures?

Pozzolanic materials like fly ash, silica fume or burnt rice husk ash and granulated blast furnace slag are examples of mineral admixtures.

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