What is admixture
Admixture is a chemical and natural substance. Admixtures are used in concrete for changing or modifying the concrete properties and Admixture is one of the main materials that is used in the concrete.
Why is admixture used in concrete?
The admixture is not a mandatory material in concrete. Concrete is a mixture of cement, fine aggregate (sand), coarse aggregate (stone), and water. Admixture is used only for the requirement to increase or decrease the concrete setting time, etc… Admixtures are mostly used in the Ready mix concrete plant (RMC), implant Rmc and construction sites. The admixtures are added before the batch or batching process runs.
Types of admixtures
They are two categories of admixtures
- chemical
- mineral
Chemical admixtures
- Plasticizers
- Superplasticizer
- Retarders and Retarding plasticizers
- Accelerators and Accelerating plasticizers
- Air-entraining Admixtures
- Damp-proofing and Waterproofing Admixtures
- Water retaining
- Dual function or Multiple admixtures
- Specially admixtures
- Corrosion inhibitors
- Shrinkage reducing admixture
- Alkali (Aggregate reaction inhibiting admixture)
- Pozzolanic
- Gas forming admixtures
- Grouting admixtures
- Workability admixtures
- Bonding admixtures
- Fungicidal, Germicidal, and Insecticidal admixtures
Mineral admixtures
- Fly ash
- Silica fume
- Blended hydraulic cement
- Metakaolin
- Rice Husk
- Volcanic ash
- GGBFS
Chemical admixtures are
Plasticizers Admixture
- The plasticizer is used to reduce the water content in concrete without affecting the workability of the concrete. It achieves high strength by decreasing the water-cement ratio at the same workability. That enables approximately 15 to 20% less water content in the production of concrete.
- This chemical is commonly used in PVC (polyvinyl chloride), polymers like plastics, and rubber. Because it makes it softer and more flexible, plasticity increases, viscosity, and friction decrease its handling in manufacturing.
Superplasticizers Admixture
- Superplasticizers, this admixture is the next level of plasticizers. The reduction of water content in concrete is higher, compared to plasticizers and makes high strength.
- This admixture is used in concrete as a low slump in slump cone test into a flowing and pourable. This concrete is easily placed.
- This concrete is to improve workability, increase strength, conserve cement, speed finishing and help to reduce shrinkage and thermal cracking.
- This chemical enables approximately 30% or more to allow reduction in water content.
Retarder and Retarding plasticizer
- Retarder and Retarding plasticizer admixtures are used in concrete to slow down the rate of the setting time process in the concrete, by slowing the initial setting time. Also to increase the workability of concrete
- Concrete is set easily in hot weather and concrete also is a high-temperature component, so this admixture is used in concrete
- Retarder admixture is mostly used to transport the concrete from one place to another place (if its need). Otherwise, the uses of this chemical are low.
- This chemical is not used in cold weather
- The water-cement ratio is only affected by using retarders. Complex concrete placement of grouting.
Did you know?
Sugar is a well-known “retarder” of concrete and it’s often used to help adjust the setting times, especially in emergencies
Accelerators and Accelerating plasticiser
- The accelerator admixture process is the opposite of the retarder admixture
- This chemical is used to increase the setting time of concrete by increasing the initial setting time
- Increase the rate of hydration value of hydraulic cement and shorten the time
- Calcium chloride is a well-known accelerator chemical
- A calcium chloride of 2% by volume is a standard calcium amount to increase the setting time of the concrete. (the volume of calcium is changed by the requirements)
- Used in wintertime and to prevent frost damage in concrete.
Air-entraining admixture
- Air-entraining admixture, chemical creates the microscopic air bubble during the mixture of cement paste and prevents the air from entraining the concrete
- The air bubble is tightly bonded so the water also struggles to enter the concrete
- The bubble usually increases its resistance to freeze-thaw and also improves the workability
Dampproof and Waterproofing
- The Dampproof and waterproofing admixture is preventing the water from entering the concrete
- This admixture is widely used in the damp course in the building at the above plinth level surface and the waterproofing structures, like a dam, etc…
- Also used in the substructure of the building and the structure
Water retaining
- Water retaining admixtures are used in concrete to increase the strength and workability of concrete and to reduce the cost
- Improve the stability of concrete mix ratio made with poor-quality aggregate
- The durability of concrete is to increase and reduce the separation of water (bleeding)
- The surface of the concrete is improved and the architectural quality
Dual function or Multifunction
- Dual function or Multifunction admixture, the single admixture can do multiple functions.
- The addition of two or more admixtures or single admixtures can do dual or multiple functions.
- Like, the conflicted bond retarder improves both mixing water efficiency and delays the initial setting time of concrete
Corrosion inhibitors
- Corrosion inhibitors are primarily used in reinforced cement concrete
- to prevent the corrosion of steel in the structure
Shrinkage reducing
- Shrinkage-reducing admixtures used in concrete to reduce the level of shrinkage in concrete
- They are used in a rather large amount in contrast to other concrete admixture
- Shrinkage is reduced and it also directly follows the less energy is available for deformation
Pozzolana admixture
- Pozzolana is an admixture for the replacement of the cement
- Pozzolana is a broad class of siliceous and luminous material
- Adding to the existing concrete mix without removing an equivalent amount of cement increases the paste content and decreases the water-cement ratio. Adding more pozzolana to a mix changes the mix proportions
Gas forming
- Gas-forming admixture is preventing the settlement and bleeding by creating bubbles in the mix, like water-entraining admixture
- The admixture help maintain the concrete initial volume, And it’s also lightweight concrete
- Hydrogen peroxide, aluminium powder, or activated carbon is used to make lightweight concrete
Mineral admixtures are
Fly ash
- Fly ash is a replacement material for cement in some volume
- Fly ash is a coal waste product that acts a lot like cement
- Improve the workability of concrete and the strength and durability of hardened concrete
- The addition of Fly ash and some amount of cement may be reduced
Silica Fume
- Silica fume also known as micro silica, is an amorphous polymorph of silica dioxide.
- A sufficient quantity of silica helps for the formation of di-calcium and tri-calcium silicates
- Improves the strength of cement and decreases the setting time of cement
Blended hydraulic cement
- Blended hydraulic cement consist of an intimate and uniform blend of ordinary portland cement and fine pozzolanic material
- The cement in which part of the clinker is substituted with other materials
Metakaolin
- Metakaolin is a DE hydroxylated form of the clay mineral kaolinite
- metakaolin has a smaller particle size and higher surface area compared to portland cement, but a larger than silica fume
- Metakaolin is a pozzolan. the most effective pozzolan material for use in cement
Rice husk and volcanic ash
- Rice husk is used in a fine state and adds the additional product of concrete. Rice husk is a by-product of rice
- Volcanic ash is used as fly ash, but the properties are changed for both ash
GGBFS
- GGBFS (Ground granulated blast-furnace slag)
- This is a cementitious material whose mail is used in concrete and is a by-product of the blast furnaces used to make iron
- Blast furnaces operate at temperatures of about 1500 degrees Celsius and are fed with a carefully controlled mixture of iron ore, coal, and limestone.
NOTE
- All admixtures are used for the unique purpose
- The volume of admixture and need for admixture is based on the requirement