Concrete Additives: An Easy Guide for All Novices
Concrete admixtures refer to those ingredients that are used with cement or water before or after the mixing. Concrete admixtures can be classified into several different categories based on their function. Each of them plays a specific role during the construction process.
Concrete Additives and Their Classifications
- Air entraining admixtures
- Plasticizers
- Water reducing admixtures
- Retarding admixtures
- Accelerating admixtures
- Corrosion inhibitors
- Hydration control admixtures
- Shrinkage reducers
- Colouring admixtures
- Alkali-Silica reacting inhibitors
- Other miscellaneous admixtures such as bonding, damp-proofing, workability, permeability reducing, gas-forming, anti-washout, grouting, foaming and pumping additives.
Concrete should have several different qualities like workable, strong, durable, finishable, wear-resistant and water-tight. These qualities of concrete can easily be obtained are economic in nature when you select the right kind of materials instead of resorting to admixtures. The main reasons why we use concrete additives are:
1. To help reduce the cost of construction.
2. To help maintain the quality of the concrete during different stages of mixing, transporting, placement and curing of the concrete in adverse weather conditions.
3. To achieve different properties of the concrete more effectively than any other means.
4. To help overcome emergencies during the concrete operations
Despite all the benefits that we can get from good concrete admixtures, there is however no sort of substitute for good concreting practises. The effectiveness of any additive depends upon different factors like the brand or the type or even the amount of the cementing materials; aggregate shape; water content; and the temperature of concrete.
Different Concrete Additives and Their Uses
1. Air entraining admixtures are used for the purpose of introducing and stabilizing microscopic air bubbles in to the concrete. Air entrainment dramatically improves the durability of the concrete when the concrete is being constantly exposed to the cycles of thawing and freezing.
2. Water reducing admixtures help in reducing the quantity of the water that is required while producing the concrete of a certain slump, reduce cement content, reduce the ration of the water to the cement or increase the slump. Typically these reduce the water content by approximately 10%. High range water reducers generally work way better than the regular water-reducing additives.
3. Super plasticizers are added to the concrete to make a high-slump flowing concrete. Flowing concrete is very fluid but workable concrete which can be placed with little or no compaction while still remaining exceptionally free of bleeding. The effectiveness of this kind of concrete additive gets increased due to an increased amount of cement in the concrete.
4. Retarding additives are generally used in delaying the rate of the setting of concrete. It is also used in decreasing the slump loss and to extend the workability.
5. Hydration control additives became available in the late 1980s. These are generally used in stopping the hydration of the cementing materials. This additive does not have a standard specification as of now.
6. Accelerating admixtures help in accelerating the rate of setting of concrete at an early stage.
7. Corrosion inhibitors are used in the construction of those structures where chlorine salts are present at large. The chloride can degrade the steel thereby making the structures weaker. These additives chemically stop the corrosion reaction from happening.
8. Shrinkage reducing additives are used wherever cracks and crevices have to be minimised in order to maintain the durability and the aesthetics of those structures.
9. Chemical admixtures were introduced in order to reduce the alkali-silica reactivity.
10. Natural and synthetic materials are used in order to colour the concrete. These are widely used mainly for aesthetic purposes.