Concrete is the single most widely used construction material in the world. It has been used in construction for thousands of years. Concrete is made using cement, aggregates, and water. However, the definition of concrete has altered in this modern era. Nowadays, it is not only considered a cementitious material, rather concrete is a high-performance material suitable for a wide variety of use case scenarios. Concrete is now used twice as much in construction as all other building materials. Hence, an emphasis on quality, performance and sustainability is essential for the industry to grow and thrive.

There was a time when concrete was simply a mixture of cement, water, and aggregates. We were bound by its properties and acted in accordance with the will of the material. For instance, concrete starts the hardening process as soon as the mixture is prepared. We had to place concrete before its initial setting time to get the best performance out of it. But now, one of the most important ingredients in high-performance, long-lasting, and durable concrete produced today are chemical admixtures. These chemical admixtures can enhance or alter the properties of concrete as per construction requirements. Hence, the workability increases, and workers can easily manipulate the properties of concrete. Choosing the right admixture for your Ready-Mix Concrete recipe is critical for producing long-lasting and high-performance concrete. In this article, we are going to discuss a variety of admixtures that are used in the preparation of Ready-Mix Concrete.

What is Admixture?

Admixture is a special ingredient that is added to the mix immediately or during concrete mixing to enhance the properties of concrete. These materials are different from the aggregates, water, and cement that are generally added to prepare concrete.

There are different types of admixtures available. These can alter the behavior of concrete separately to suit a range of weather conditions. Admixtures can minimize the construction cost, increase the quality and performance, enhance workability, ensure the quality of concrete during mixing, transporting, placing, and curing, and overcome certain emergencies during concrete operations.

Successful integration of admixtures depends on the appropriate methods of batching and concreting. Most admixtures are available in ready-to-use liquid form and are added to the concrete at the plant or the job site.

The effectiveness of an admixture depends on several factors including type and amount of cement, aggregates, water, mixing time, slump, and temperature of ambiance and concrete. Try to find a reliable Ready-Mix Concrete supplier who can address your concreting needs appropriately.

Functions of Concrete Admixtures

The admixtures are added to the concrete mix to attain certain properties. The basic function of these admixtures is:

• To increase or decrease the setting time of fresh concrete
• To enhance the workability or flowability of concrete mix
• To enhance the durability and strength of concrete
• To reduce the permeability of concrete
• To reduce the segregation and bleeding of concrete during placing
• To reduce the heat of hydration
• To achieve other desirable properties

Source: Concrete Network

Types of Concrete Admixtures Used in Construction

There are many different types of concrete admixtures. Here is a list of the most important ones:

Water Reducing Admixture

As the name suggests, these types of admixtures minimize the water demand in a concrete mix. Workability can be improved in a concrete mix by adding water. But adding too much water can reduce the strength and durability of concrete. Water reducing admixtures can help to increase the workability, and strength of concrete, establish a secure bond between concrete and steel, prevent cracking, segregation, honeycombing, bleeding, etc. These admixtures are commonly known as plasticizers, and these are divided into three types. These are plasticizers, mid-range plasticizers, and superplasticizers. The regular ones can reduce the water demand by up to 10%, mid-range plasticizers can reduce up to 15% of water demand while superplasticizers can do it by 30%. Calcium, sodium, and ammonium lignosulphonates are commonly used water-reducing admixtures. However, superplasticizers are advanced in nature and made with acrylic polymer, polycarboxylate, multicarbovylatethers, etc.

Retarding Admixtures

Retarding admixtures can slow down the rate of hydration of cement in its initial stage. The initial setting time of concrete is also increased. Retarding admixtures are commonly known as retarders and are used especially in high-temperature zones where concrete can be set relatively quickly. In some cases, quick setting in some situations may lead to discontinuities in layers of concrete. It can damage the structure, cause poor bond formation between the surfaces, create unnecessary voids in concrete etc. Retarders are very helpful to eliminate such scenarios. Some common types of retarders are calcium sulphate or gypsum. Starch, cellulose, common sugar, and salts of acids can also be used as retarding admixtures. Some water-reducing admixtures can also act as retarding admixtures. These are known as retarding plasticizers.

Accelerating Admixtures

This type of admixture can help to reduce the initial setting time of concrete. It can react with the components of the concrete to speed up the process of the initial stage of hardening concrete. Accelerating admixtures can also help to improve the strength of concrete in the early stage by increasing the rate of hydration. The early setting of concrete can be helpful in many situations where faster construction is necessary. Hence, formworks can be removed sooner. The curing period can also be cut down. It is especially helpful in emergency repair works and constructions in low-temperature regions. Some accelerating admixtures are triethanolamine, calcium formate, silica fume, calcium chloride, finely divided silica get etc. Among these, calcium chloride is the cheapest and most commonly used option.

Air Entraining Concrete Admixture

The development of air entraining admixtures is widely regarded as a major milestone in the history of the concrete industry. Their main purpose is to make concrete more resistant to damage from temperature changes. These admixtures, when applied to concrete, generate millions of tiny air bubbles that do not coalesce, enhancing the material’s strength and durability. Higher workability, reduced segregation and bleeding decreased unit weight and modulus of elasticity, enhanced chemical resistance and decreased cement, sand, and water content are only some of the benefits of air entrainment in concrete. Popular air entrainment admixtures include vinsol resin, darex, teepol, cheecol, etc. Natural wood resins, alkaline salts, animal and vegetable fats and oils, and so on are the main components of these admixtures.

Pozzolanic Admixtures

A dense concrete mix, made with pozzolanic admixtures, is ideal for water-retaining structures like dams, reservoirs, etc. They also lessen thermal expansion and hydration heat. The best pozzolanic materials, used in the right amounts, achieve good performance and eliminate or greatly decrease numerous potential dangers, such as alkali-aggregate reaction, leaching, sulfate attack, etc. Admixtures such as pozzolanic materials might be either natural or synthetic. Clay, shale, volcanic tuffs, pumicite, and so on are all examples of naturally occurring Pozzolanic materials; man-made pozzolans include fly ash, silica fume, blast furnace slag, rice husk ash, surkhi, and so on.

Damp Proofing Admixtures

In order to make the concrete building impermeable to water and to avoid dampness on the surface of the concrete, damp proofing or waterproofing admixtures are utilized in the construction process. In addition to having the quality of being water resistant, they also operate as accelerators in the early stage of the hardening process of concrete. There is a liquid form, a powder form, a paste form, and other forms that damp proofing admixtures can be found in. Aluminum sulfate, zinc sulfate, aluminum chloride, calcium chloride, silicate of soda, and other chemically active pore fillers are the primary components of these admixtures. Other components include aluminum chloride and calcium chloride.

Gas Forming Admixtures

Chemical admixtures that produce gas include aluminum powder, activated carbon, and hydrogen peroxide. As the cement hydrates, it releases hydroxide, which combines with gas-forming admixtures to produce tiny bubbles of hydrogen gas throughout the concrete. Many parameters, including the amount of admixture, the chemical composition of the cement, the temperature, the fineness, etc., influence the range of bubble formation in concrete. The concrete’s ability to resist bleeding and settlement is enhanced by the bubbles that form during the curing process. There are other gas-forming admixtures used in the making of lightweight concrete. Gas-forming admixtures are often employed at a concentration of 0.5 to 2 percent by weight of cement to prevent settlement and bleeding. However, when building lightweight concrete, a larger quantity is often recommended, as much as 100 grams per bag of cement.

Air Detraining Admixtures

The voids in concrete can be made smaller by adding an air-detraining admixture to the mix. It is possible that the aggregates will release the gas into the concrete, in which case the amount of air entrained will exceed the necessary amount. In such cases, using this type of admixture becomes a necessity for ensuring the durability of concrete. Trisodium phosphate, silicones, and water-insoluble alcohols are just a few of the most common air-detraining admixtures.

Alkali Aggregate Expansion Preventing Admixtures

The alkali of the cement reacts with the silica in the aggregates, causing the aggregates to expand. It turns into a gel and causes concrete to expand in volume, which can cause cracks and eventually crumble away. In order to avoid the alkali-aggregate reaction, pozzolanic admixtures can be used, and in some cases, air-entraining admixtures can be of assistance as well. Aluminum powder and lithium salts are two common admixtures used to lower the potential for an alkali-aggregate reaction.

Anti-washout Admixtures

It is common practice to incorporate anti-washout admixtures into concrete for submerged concrete structures. The concrete mixture is protected from being washed away by the water. It makes concrete more cohesive. Natural or synthetic rubbers, cellulose-based thickeners, etc., are used to create these admixtures.

Grouting Admixtures

In order to get the desired qualities of the grout, admixtures are added to the grout components. Depending on the depth of the cracks or fissures, you may need either a quick-setting or a slow-setting grout. Because of this, various admixtures are utilized as grout admixtures depending on the circumstances. Grout admixtures, such as calcium chloride, triethanolamine, and others, are used to speed up the setting time of the grout. Retarders, such as mucic acid, gypsum, etc., are used to delay the grout’s setting time in the same way. To prevent foundations from sinking, gas-forming admixtures like aluminum powder are blended with grout.

Corrosion Preventing Admixtures

Steel reinforcing in a concrete building is susceptible to corrosion in the presence of salt water, industrial gases, chlorides, and other aggressive chemicals. Corrosion prevention admixtures are used to halt or slow the corroding process. Sodium benzoate, sodium nitrate, sodium nitrite, etc. are all examples of corrosion-preventing admixtures used in reinforced concrete.

Bonding Admixtures

Concrete surfaces, both new and old, can be bonded together with the use of bonding admixtures. It is not uncommon for new concrete to fail when put on top of older, hardened concrete because of a lack of a strong link between the two. Bonding admixtures are added to cement or mortar grout that is spread over the concrete’s surface just before new concrete is poured. Overlays, screeds, and repairs are just some of the many uses for these admixtures in the construction industry. Water emulsions and bonding admixtures can be formulated from natural or synthetic rubber, as well as polymers such as polyvinyl chloride, polyvinyl acetate, and others.

Fungicidal, Germicidal, Insecticidal Admixtures

Concrete mixes with fungicidal, germicidal, and insecticidal qualities are recommended to reduce the likelihood of bacterial, fungal, and insect growth on finished constructions. To improve these characteristics, admixtures such as polyhalogenated phenols, copper compounds, dieldrin emulsions, etc., can be added to the combination.

Coloring Admixtures

The pigments used to give the final product of concrete its desired hue is known as coloring admixtures. There should be no negative impact on the concrete’s durability from the coloring admixtures. When cement is mixed with coloring admixtures in a ball mill, the resulting-colored cement can be used to create colored concrete. Below is a table displaying the results of using various colored admixtures:

Source: The Constructor

Summary

Admixtures have become increasingly popular in the Ready-Mix Concrete industry. Its usage can enhance the performance and quality of concrete by a large margin. However, it is very crucial to know what type of admixture to use in which scenario. Because some admixtures can nullify the effect of others while others can increase it. It is better to discuss with your contractor and manufacturer beforehand about admixtures. Modern architecture demands strong durability and strength from concrete. Traditional concrete sometimes cannot provide the requirements to implement complex plans. It is expected that the concrete admixture market will experience positive growth in the upcoming years.

Frequently Asked Questions (FAQs)

What is a concrete admixture in simple terms?

Ans: Concrete admixtures are natural or synthetic elements that can enhance specific properties of concrete.

What is the most common type of admixture used in concrete?

Ans: The most common types are air-entraining admixture, accelerating admixture, water reducing admixture, and retarding admixture.

Are chemical or natural admixtures better for concrete?

Ans: As long as the admixture satisfies your requirements, both can be used.

How much admixture should I apply in concrete?

Ans: The ratio of admixtures will vary depending on the type of admixture.

What are some mineral admixtures?

Ans: Some mineral admixtures are fly ash, rice husk, metakaolin, silica fume, palm oil fuel ash, etc.