In: Civil Engineering
Fly ash is generated in combustion of coal in fine grey powder. It's spherical in shape. Fly ash is pozzalonic properties as a product from industrial plants using pulverized coal and lignite as fuel.
It is defined into two classes:
It is produced from bituminous coal. It contains Lime( less than 20% )and silica,alumina,iron( greater than 70%).
It is produced from sub-bituminous coal.it contains lime (greater than 20%).
Fly ash in concrete:
1.it Reduce Water content
2.it improve Workability
3. It reduce segregation
4.it improves pumpability
5.it improve finishing
6.low heat of hydration
7.Lower drying shrinkage
8.Improved long term strength
9. Redused efflorescence
10.Good combination protection
11.Low chloride ingress
14.Improved resistance to alkali silica reactivity and sulfate attack.
Fly ash holds a vast potential for improving the Modern day concrete when it comes to quality in long term. In spite of being industrial waste,it can improve durability and reduce heat of hydration and give more strength to concrete.
Silica fume is different from fly ash, it is generated from electric arc furnaces as a by product.it contains high SiO2, extreamly small size particle with large surface area.
Silica fume in concrete:
1.It gives high strength to concrete.
2.Water damand increase
3.No bleeding of concrete
5.Increases plastic shrinkage
6.Increases chloride permeability
7.High range of water reducers are required
8.Replace Portland cement it leads to Reduction of Co2
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