There are many admixtures commercially available can increase the strength of concrete such as pozzolanic materials (for example silica fume). Using high range water reducing admixtures (superplasticizers) can also increase the concrete strength by reducing the amount of mixing water.
I think the word "strength" involves several properties such as compression, tension, permeability, fire, ....etc.
Each property can be increased by adding special admixtures.
Best regards.
Admixtures are nothing but Ingredients used for concrete other than, Cement,Water,Aggregates and added before or during mixing.
Generally admixtures divided in to 2 parts,
1. Chemical Admixtures,
Chemical Admixtures are as fallows
* Plasticizes: Achieves higher strength by Reducing water content 5–12% for the same work-ability.
* Super plasticizes: Achieves higher strength by Reducing water content 12–30% for the same work-ability.
* Retarders: A retarder used to slows down the process of hydration so that concrete remains plastic and workable for a longer time.(ex: gypsum,sugar etc)
* Accelerator: These are added to concrete to increase the rate of early strength to permit earlier removal of formwork (ex: calcium chloride)
* Air entraining agents: used to reduce the bleeding,and permeability
2. Mineral admixture
* Fly ash: Helps to reduce, bleeding,segregation in fresh concrete.And it significantly improves the long term strength and durability and reduce heat of hydration.
* Silica Fume: it is also helps to reduces bleeding & Segregation. It is used to increase the Initial slump of concrete to assist in pumping long distances, especially vertically.
* GGBS: GGBS helps in reducing W/C ratio. Used for Better work-ability, making placing and compaction easier. Increased resistance to chemical attack. helps to achieve higher ultimate strength.
Admixtures are using to improve the strength of concrete as Silica fume , Rubber, Lime, Fly ash, Fibers and Polymers. In recent time Nano technology using to improve the strength and properties of concrete as nanosilica , nanosilica and nanolime . Nano additive succeed to good improvement the strength and properties of concrete but the disadvantage of nano additives is high price.
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