In the history of construction, concretes are the most commonly used building material in the world. It is made up of Portland cement, water, and aggregates (gravel, sand, or rock). When mixed, they form a workable paste that gradually hardens over time through the curing process. For instance, concrete is widely utilized in structures such as buildings, bridges, highways, and dams.
There are various major procedures to consider while manufacturing construction concrete, including material selection and grading, size, and shape, combining with water, controlling mixture proportions and temperature during pouring into forms, and curing or hardening of the concrete. Concrete admixtures are important in this case.
What is Concrete Admixture?
Concrete admixtures are one of the most crucial elements of today’s highly effective, reliable, strong, and appealing concrete. During the mixing process, concrete admixtures are such ingredients that are mixed with fresh or hardened concrete to enhance specific qualities of the concrete, such as effectiveness, longevity, and absolute strength.
Why use Concrete Admixture?
For the following reasons, you should consider using concrete admixture.
- To make concrete stronger and more durable.
- Speed up or slow down the process of determining the initial setting time of concrete.
- Reduce the permeability of concrete.
- Minimizing hydration’s heat.
- Produce lightweight concrete.
- To improve the workability of concrete.
- Preventing Concrete from Corrosion.
- Reduce segregation and bleeding of concrete.
- To improve the bond between steel reinforcement and concrete.
- Build a connection between the old and new concrete.
- To limit the growth of the alkali-aggregate.
- To strengthen defenses against the sulfate attack.
Types of Concrete Admixture
There are mainly two types of concrete admixture, which include:
- Chemical Admixture
- Mineral Admixture.
Chemical admixtures are chemical additives that are used with concrete to change its characteristics and give it particular features. Chemical admixture are mainly classified into five categories:
- Water-reducing admixture.
- Super-plasticizing /High Range Water Reducer,
- Retarding Admixture.
- Air Entraining Admixture.
- Accelerating Admixture.
On the other hand, mineral admixture are siliceous and insoluble components other than cement and aggregate that are typically added to concrete in higher proportions to increase workability, resistance to heat cracking, alkali-aggregate expansion, and sulfate attack, as well as to allow for cement content reduction. The following are some mineral admixtures that are typically used in concrete.
- Fly ash.
- Silica fume.
- Ground-granulated blast furnace slag.
Now let’s take a deeper look at chemical admixture. The following chemical additives are popular and often used with concrete:
1. Water-reducing Admixture
Water-reducing admixtures are mostly used to decrease the water content of the concrete mix, often by 5–10%, sometimes even up to 15% (in extremely workable concrete). To reduce the water-to-cement ratio while maintaining the necessary workability, a water-reducing admixture is used in concrete mixes. Nearly most of the water-reducing admixtures are intended for use in ready-mixed and truck-mixed concrete.
Water-reducing admixtures are also known as “plasticizers,” and these are classified into three categories.
- Mid-range plasticizers
Normal plasticizers can reduce water consumption by up to 10%, mid-level plasticizers can reduce water demand by up to 15%, and superplasticizers can reduce water usage by up to 30%. Calcium, sodium, and ammonium lignosulphonates are the most commonly used plasticizers.
2. High Range Water Reducing (HRWR) Admixture
Superplasticizers are also known as “high-range water-reducing admixtures” due to their ability to reduce the mixing water in a concrete mixture three to four times more when compared to normal water-reducing admixtures.
HRWR admixtures work in a similar way to conventional water-reducing admixtures, with the exception that they are more effective at dispersing fine-grained materials like cement, fly ash, powdered granulated blast-furnace slag, and silica fume. Part of the HRWR admixtures has a slump-increasing effect in concrete for just 30 to 60 minutes, after which the concrete will restore its previous slump.
Some of the latest generations of superplasticizers include:
- Acrylic Polymer-based.
- Polycarboxylic ether (PCE) based.
- Sodium Naphthalene Formaldehyde (SNF) based.
Difference between PCE-based and SNF-based admixture.
Among these admixtures, the Superplasticizers Polycarboxylic Ether (PCE) and Sodium Naphthalene Formaldehyde (SNF) have significant importance.
SNF is a linear polymer, whereas PCE is a comb copolymer with an adsorbing backbone and nonadsorbing side chains. Both are known to adsorb on cement particles or agglomerates, dispersing and boosting flowability.
However, SNF uses electrostatic repulsion to spread cement particles and decrease attractive interparticle interactions such as van der Waals forces, whereas PCE uses both electrostatic repulsion and steric hindrance between nonadsorbing side chains. In Self-Consolidating Concrete (SCC), SNF appears to be more robust. On the other hand, PCE is more stable and less impacted by quick gypsum production during early hydration than SNF, and it is more efficient in minimizing dynamic yield stress.
3. Retarding Admixture
Retarding admixtures reduce the early hydration of cement and increases the first setting time of concrete. These admixtures are particularly useful in high-temperature areas where concrete sets quickly. Retarders are effective in eliminating this sort of issue, such as rapid setting in particular cases, which leads to structural discontinuities, a weak bond between the surfaces, unwanted holes in the concrete, and so on. Calcium sulfate and gypsum are two popular retarding admixtures.
There are two techniques for making retarder mixtures:
- Organic Substances
- Inorganic substances
Organic retarders are made from the following chemicals: lignosulphonates, hydroxycarboxylic acids, salts, phosphonates, and sugars. On the other hand, inorganic retarders produced from phosphates, magnesium salts, fluorites, and borates are also available. Most water-reducing admixtures also function as retarding admixtures and are known as retarding plasticizers.
The use of retarding admixture is effective in the following situations:
- The use of retarders is effective in the following situations:
- Complex concrete installation or grouting.
- A unique architectural surface finish.
- Adjusting for the accelerating impact of high temperatures on the first set.
- Preventing cold joint development in subsequent lifts.
4. Air Entraining Admixture
One of the most significant inventions in concrete technology is air-entraining admixtures. Their major role is to strengthen the durability of concrete when it is frozen and thawed. When these admixtures are added to the concrete mix, they generate millions of non-coalescing air bubbles throughout the mix, improving the characteristics of the concrete.
The primary objective of air entrainment is to enhance the durability of hardened concrete, particularly in freeze-thaw conditions; the secondary goal is to improve the workability of the concrete while it is in a plastic state. Air entrainment in concrete will also minimize segregation and bleeding, lower its unit weight and modulus of elasticity, improve its chemical resistance, and reduce its cement, sand, or water content, among other benefits.
Vinsol resin, Darex, Teepol, Cheecol, and other air entrainment admixtures are the most widely employed. These admixtures are composed of natural wood resins, alkali salts, animal and vegetable fats, oils, and other substances.
5. Accelerating Admixture
Accelerating admixtures are used in concrete to decrease the initial setting time. They accelerate the early stage of concrete hardening, which is why they are also known as “accelerators.” These accelerators help increase the early strength of concrete by increasing the rate of hydration. Some of the accelerating admixtures are triethanolamine, calcium formate, silica fume, calcium chloride, finely split silica gel, and so on. Among them, calcium chloride is a frequent and affordable accelerating admixture.
Accelerating Admixtures are effective in a variety of scenarios, including:
- Early formwork removal.
- In a shorter drying period.
- Emergency repair work.
- Construction in cold temperatures.
Apart from the main five concrete admixture, several different chemical concrete admixture are widely used today, such as Damp Proofing Admixture, Alkali Aggregate Expansion Preventing Admixture, Anti-washing Admixtures, and Corrosion Inhibiting Admixture.
6. Damp Proofing Admixture
Dampproofing, also known as waterproofing admixtures, is used to make the concrete structure resistant to water and to avoid dampness on the concrete surface. In addition to being water resistant, they also function as accelerators in the early phases of concrete hardening. Dampproofing admixtures come in liquid, powder, paste, and other forms.
7. Alkali Aggregate Expansion Preventing Admixture
The interaction of the alkali in the cement with the silica in the aggregates causes alkali-aggregate expansion in concrete. It creates a gel-like material and induces volumetric expansion of the concrete, which can result in cracking and disintegration. To inhibit the alkali-aggregate reaction, pozzolanic admixtures and, in certain situations, air-entraining admixtures are used. Aluminum powder and lithium salts are often used as admixtures to lessen the possibility of an alkali aggregation reaction.
8. Anti-washout Admixtures
Anti-washout admixtures are sometimes called water-retaining or viscosity-modifying admixtures. These admixtures increase the stability, cohesion, and strength of concrete and prevent the washing away of concrete mixtures underwater. Underwater construction is the most common use for anti-wash-out admixtures. Admixtures of this sort are made from natural or synthetic rubbers, cellulose-based thickeners, and other materials.
9. Corrosion Inhibiting Admixture
Corrosion inhibitors are admixtures that either slow or stop the corrosion of implanted metal. One of the most typical construction issues is steel corrosion in reinforced concrete structures. Corrosion additives are used to prevent this issue. In reinforced concrete, commonly used corrosion-preventive admixtures include sodium benzoate, sodium nitrate, sodium nitrite, and others.
Best Admixture Company in Bangladesh
The right suppliers are essential for understanding which concrete admixture to use and how to employ them. Franklin Floortech is a group of skilled engineers with expertise in the chemical and construction sectors. To face these challenges and be the best, we set out on our journey in 2008. We completed numerous projects that pleased our clients. Franklin Floortech is always on hand to offer guidance if you need help selecting the right concrete admixture for your needs.
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Concrete Admixture in Bangladesh
Franklin Floortech is the ideal choice if you are seeking the best concrete admixture to use in the construction of your dream house, a commercial building, highways, bridges, or other companies. We provide a large selection of concrete admixtures for precast concrete, waterproofing concrete, ready-mix concrete, and other applications. Franklin is a proud Berger Fosroc distributor. Our products adjust and improve the characteristics of fresh and hardened concrete or mortar. Furthermore, Franklin Floortech offers the greatest assistance and concrete admixture at the best price in Bangladesh.