Here are the types of admixtures for concrete as per IS 9103 (1999):
Accelerating Admixtures
This type of admixture expedites the setting time of concrete for faster strength development. They increase the hydration rate of hydraulic cement when added to mortar or grout. They are composed of compounds like calcium chloride, calcium nitrate, or triethanolamine. They are utilised in situations where faster setting times are required, such as in cold weather conditions or for rapid construction schedules.
Retarding Admixtures
Retarders work oppositely to accelerators. They slow down the setting time of concrete. These are helpful when the concrete needs to travel long distances in special mixers or when it is hot outside. Retarding admixtures are especially handy as a grouting mix and work to reduce the water used. The hydroxyl carboxylic acid is a type of admixture that makes concrete with a bit less water than the quantity of water used in a regular mix. Using these admixtures can make the concrete last longer and be sturdier.
Water-reducing admixtures
These are the types of admixtures that enable the reduction of water content in the concrete mix without compromising its workability. They enhance the flowability of concrete, allowing for easier placement and better compaction. Using this admixture comes in handy in various scenarios. Pouring concrete is tricky because there are lots of bars or other elements in the way. Also, when the mix of concrete is tough, like when crushed rocks are used, this admixture can make the concrete more workable. Additionally, by adding this admixture, the cost of cement used in making concrete can be reduced by a notable amount. Common water-reducers include polycarboxylate ethers ir lignosulfonates.
Air-entraining admixtures
These admixtures introduce microscopic air bubbles into the concrete mixture during mixing. By altering the surface tension of the mixing water, they allow air bubbles to form and disperse uniformly throughout the concrete. These bubbles enhance the concrete’s durability by improving its resistance to freeze-thaw cycles, reducing bleeding, and improving workability. These are composed of agents like vinsol resin or salts of petroleum acids.
Super plasticising admixtures
Superplasticisers are advanced water-reducing agents that greatly enhance the workability of concrete without increasing water content. They significantly improve the flow characteristics of concrete, allowing for easier placement in congested reinforcement areas. Compounds such as sulfonated naphthalene formaldehyde condensate (SNF), polycarboxylate ethers (PCE), and melamine-based superplasticisers fall into this category.
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