What Are Concrete Additives? Why Do We Use Them?
What Are Concrete Additives?
A concrete admixture refers to the components of concrete that are added just before the mixing process to improve the quality, manageability, acceleration or to delay the setting time of concrete. The successful use of admixtures depends on the combination of ingredients and concrete. Most admixtures are available in ready-to-use liquid form and are added at the factory or construction site. Some additives like pigments, extenders and pumping agents are used in very small amounts.
Types Of Concrete Additives
Water Reducing Admixtures
Water-reducing admixtures are used to make concrete, mortar or grout more workable without the need of adding more water. There are three types of water-reducing concrete additives-superplasticizers, mid-range plasticizers and plasticizers which cut the water requirement by 30%, 15% and 10% respectively.
Admixtures that delay cement’s initial rate of hydration and prolong its setting time are known as retarders. Gypsum and calcium sulphate are the most commonly used retarding admixtures. Other substances used as retarders are starch, cellulose derivatives, ordinary sugar and acid salts.
Accelerating admixtures speed up the initial setting time of concrete thus increasing its early-stage strength. Common accelerators used are silica fume, calcium chloride and finely divided silica gel.
Air Entraining Concrete Admixture
Air entraining chemical admixtures are used for increasing the durability of concrete during freezing, dewatering and thawing. When they are used, they create air bubbles that improve the characteristics of the concrete.
Air Detaining Admixtures
To get rid of the extra air from the concrete voids, air detraining admixtures are used. When the air-entrained is more than adequate in concrete due to gas leakage from aggregates, they are useful. Tributyl phosphate, silicones, water-insoluble alcohols are some of the most common air entrained admixtures.
Why Are They Used?
Besides cement, sand and water, any other substance added to concrete is an additive. Even though they are not always needed, they can serve as auxiliary forces under specific conditions.
The main reason why a concrete admixture is used is to reduce the cost of concrete construction, increase productivity, improve the performance of hardened concrete, ensure the quality of concrete in the mixing, transportation, pouring and curing processes and to overcome certain construction emergencies.
Admixtures are also used to accelerate or retard the set time of concrete and reduce its water demand, shrinkage and bleeding. When choosing an additive, it is important to consider the expected outcome and how it relates to the site conditions. Additives can also be employed as an emergency measure to solve implementation challenges if project managers face any difficulties during the construction phase.
It is also possible to improve the effectiveness and resistance of concrete in natural conditions by applying engineering science, modifying the ingredients, examining the type of concrete and water-cement ratio. If it is impossible due to special circumstances like frost, high temperatures, increased abrasion or prolonged exposure to deicing salts or other chemicals, concrete additives are added to concrete.
The chemical reaction between cement and water generates heat and increases the temperature of concrete. The rise in temperature depends on the quantity and properties of the cement and the degree of cooling done during concrete production. At the centre of large blocks of concrete in foundations or rafts, the temperature can rise 13 degrees per 100 kg of cement per cubic meter of concrete. A large temperature rise due to the utilization of rich mixes in large pours can lead to a temperature differential between the interior and exterior surfaces of the concrete. This can lead to thermal cracking.
A reduction in the amount of cement can reduce the heat of hydration and mitigate the problems associated with it. If a plasticizer is used, the cement consumption can be greatly reduced without a change in the water cement ratio or strength.
Currently, new chemical admixtures are being developed. Reducing the need for Portland cement has a positive impact on the environment and can reduce pollution. To make concrete self-healing, different types of admixtures are being researched. Future construction of buildings, roads and other structures will lead to rise in demand for concrete admixtures.
Vinati Organics is the world’s largest manufacturer of IBB, ATBS and concrete additives. We blend innovation with chemistry to offer value-added products to our varied clientele. Since our inception in 1989, we have evolved from a company manufacturing a single product to an integrated business that offers a plethora of chemical products to the largest industrial and chemical companies in the US, Europe and Asia.
All our products are manufactured in two state-of-the-art facilities in Maharashtra which are integrated with B2B business model. They are equipped with the latest advanced technologies and adhere to green practices that minimize environmental footprints.