Published on March 20, 2018
EFFECT OF CEMENT REPLACEMENT BY FLY ASH AND SILICA FUME. K . ravi arunachalam: EFFECT OF CEMENT REPLACEMENT BY FLY ASH AND SILICA FUME . K . ravi arunachalam Context : Context What is fly ash? Properties of fly ash. Role of fly ash in cement. Pros and cons of fly ash in cement. What is silica fume? Properties of silica fume. Role of silica fume in cement. Pros and cons of silica fume in cement. Advantage of use of fly ash and silica fume in cement. What is fly ash?: What is fly ash? Fly ash: It is also known as "pulverised fuel ash“ one of the coal combustion byproduct. Components present: silicon dioxide (SiO 2 ) aluminium oxide (Al 2 O 3 ) calcium oxide (CaO) Main byproduct : Thermal power plants. Types of fly ash: Types of fly ash Fly ash are of two types. Class F By product of burning anthracite or bituminous coal. contains less CaO . Less cementing property. Class C . By product of burning lignite or sub bituminous coal. Contains large amount of CaO. More cementing property. Properties of fly ash: Properties of fly ash High fineness Low carbon content Good reactivity High content of CaO Considerable cementing property Spherical in shape is essential that improves Flow ability and reduces the water demand of concrete. Effects :: Effects : Fly ash is mixed 30-35% in cement based on the weight of cement. At initial stage strength of fly ash concrete is less compared to the concrete with out fly ash but after setting time the strength of fly ash concrete will comparatively high. Curing of fly ash concrete needs longtime. Dams with fly ash concrete has improved long term strength and water tightness. Strength gain of fly ash concrete: Strength gain of fly ash concrete Advantages or pros: Advantages or pros Fly ash in the concrete mix efficiently replaces Portland cement that in turn can aid in making big savings in concrete material prices. It is also an environmentally-friendly solution, which meets the performance specifications. It improves the strength over time and thus, it offers greater strength to the building. It effectively combines with alkalis from cement, which thereby prevents the destructive expansion. It produce less heat and prevent thermal expansion. Disadvantages or cons: Disadvantages or cons The quality of fly ash to be utilized is very vital. Poor quality often has a negative impact on the concrete. The poor quality can increase the permeability and thus damaging the building. Slower Strength Gain Example for fly ash concrete: Example for fly ash concrete Rihand irrigation project, Uttar Pradesh. What is silica fume?: What is silica fume? It is also called micro silica. Byproduct of silicon or ferrosilicon alloy production. Spherical in shape. 100 times smaller than average cement particle. Contains 85% of SiO₂ content. Properties of silica fume: Properties of silica fume Silica fume is an ultrafine material . bulk density of silica fume varies from 130 to 600 kg/m 3 . The specific gravity of silica fume is generally in the range of 2.2 to 2.3. It better fill voids between cement particles and result in dense concrete having high compressive strength and extremely low permeability. Role of silica fume in concrete: Role of silica fume in concrete Micro silica make the fresh concrete sticky in nature and hard to handle. Large reduction in bleeding of concrete this will make concrete easy to transport and handle without segregation. It is prone to plastic shrinkage cracking and therefore sheet or mat curing is essential. A strength of 60-80 MPa can be achieved easily using silica fume concrete. Role of silica fume: Role of silica fume Advantage or pros: Advantage or pros Lowers concrete permeability. Significantly increase concrete durability. Increase ultimate strength. Beneficial in high strength concrete. Improves bond strength to steel. Reduce steel corrosion. Provides excellent resistance to sulphate or seawater attack. Disadvantage or cons: Disadvantage or cons Plastic shrinkage will takes place when curing is not proper. Hard to handle but effective in strength. Example to silica fume concrete: Example to silica fume concrete Kinzua dam, US. Advantage of using fly ash and silica fume in concrete: Advantage of using fly ash and silica fume in concrete Inexpensive replacement of Portland Cement. Improves strength, segregation and easy to pump the concrete. Environmental friendly. Easy available and less cost induce to use such type effectively. Thank you for your patient listening.: Thank you for your patient listening.