Table of Contents
Several materials have recently been used for the improvement of concrete properties. Microsilica or silica fume is an excellent admixture for concrete as it leads to better engineering properties. It reduces thermal cracking, improves durability, and increases strength.
Why is micro silica used?
Used as an admixture, microsilica can improve the properties of both fresh and hardened concrete. Microsilica reduces the rate of carbonation, decreases permeability to chloride ions, imparts high electrical resistivity, and has little effect on oxygen transport.
Is micro silica waterproof?
4.4 Silica Fume Waterproof Concrete Because of its low permeability, micro-silica can be use as an integral water-proofer for below ground structures where some dampness is acceptable, eg Car parks.
Which is a property of micro silica?
Properties of Microsilica Microsilica is a grey; nearly white to nearly black powder. Spherical particles less than 1mm in diameter. The bulk density of is based on the degree of densification and varies from 130 to 600 kg/m3.
Why do we use silica fume in concrete?
Silica fume is added to Portland cement concrete to improve its properties, in particular its compressive strength, bond strength, and abrasion resistance. Silica fume also blocks the pores in the fresh concrete so water within the concrete is not allowed to come to the surface.
What are the advantages of micro silica concrete?
Several materials have recently been used for the improvement of concrete properties. Microsilica or silica fume is an excellent admixture for concrete as it leads to better engineering properties. It reduces thermal cracking, improves durability, and increases strength.
Is silica a cement?
Many common construction materials contain silica including, for example, asphalt, brick, cement, concrete, drywall, grout, mortar, stone, sand, and tile.
What are the disadvantages of high silica cement?
disadvantages of silica fume in concrete Silica fume concrete is too viscous and difficult to apply.it is not easy to wipe the surface. Silica fume requires a high amount of water and needs to be used with a superplasticizer. The price of silica fume is relatively high compared to cement and fly ash.
What is the role of alumina in cement?
Alumina: It imparts quick setting property to the cement. It acts as a flux and lowers the clinkering temperature. Alumina in excess quantity reduces the setting time of cement but simultaneously reduces the strength of cement.
What is the difference between fly ash and silica fume?
Silica Fume is typically much more reactive, particularly at early ages , because of its higher silicon dioxide content and because of its very small particle size. Disadvantages of Fly Ash: – High-carbon fly ash materials tend to use more water and darken the concrete as well.
Is silica fume expensive?
Condensed silica fume costs from $400-$1,000/ton, which is significantly higher than portland cement ($90/ton).
How is micro silica made?
Silica fume, also known as microsilica, is an extremely fine noncrystalline polymorph of silica and is produced in electric arc furnaces (EAFs) as a by-product of silicon and ferrosilicon alloy production. As just mentioned, silica fume arises as a by-product of silicon or ferrosilicon alloy formation in an EAF.
Is silica fume toxic?
Repeated exposure can damage the eyes. * High exposure to Silica, Amorphous (Fume) can cause a flu-like illness with headache, fever, chills, aches, chest tightness and cough. * Repeated exposure to Silica, Amorphous (Fume) can cause lung damage (fibrosis).
How do you mix silica fume in concrete?
(1) Put in aggregate, then put in silica fume, cement and dry mix, then add water and other additives. (2) Put in coarse aggregate + 75% water + silica fume + 50% fine aggregate, stir for 15-30 seconds, then put in cement + concrete admixture + 50% fine aggregate + 25% water, and stir until uniform.
Does silica increase strength?
Silica fume has been successfully used to produce very high-strength, low-permeability, and chemically resistant concrete. Addition of silica fume by itself, with other factors being constant, increases the concrete strength.
How does silica fume work?
When silica fume is added to concrete, initially it remains inert. Its small particle size which is 100 times finer than ordinary portland cement complements the finess modulus of concrete and provides a ball-bearing effect, which improves thixotropic behavior, in effect modifying concrete viscosity.
What is the disadvantage of silica?
Disadvantages of Silica Fume/Micro Silica In case the external temperature is high, it will lead to early dry shrinkage. Hence, it is more prone to cracks which may ultimately affect the overall strength. The construction with the silica fume concrete is difficult; as workability of silica fume concrete is poor.
What is the meaning of pozzolanic?
: finely divided siliceous or siliceous and aluminous material that reacts chemically with slaked lime at ordinary temperature and in the presence of moisture to form a strong slow-hardening cement.
Why lime is used in cement?
Lime provides high water retention that allows for maximum early curing of the cementitious materials. High initial flow which permits easy complete coverage of masonry units. The low air content of cement-lime mortar increases bond strength.
Why is silica bad for you?
Breathing in very small (“respirable”) crystalline silica particles, causes multiple diseases, including silicosis, an incurable lung disease that leads to disability and death. Respirable crystalline silica also causes lung cancer, chronic obstructive pulmonary disease (COPD), and kidney disease.
Is silica safe to take?
According to the United States Department of Labor, about 2.3 million people in the U.S. are exposed to silica at work. As long as you aren’t inhaling silica in its crystalline form, it appears to be safe to consume at the levels set out by the FDA.
How much silica does it take to get silicosis?
Because silicosis is caused by cumulative or repeated exposure to respirable crystalline silica, it makes sense that we would want to limit exposure as much as possible! OSHA has set the Personal Exposure Limit (PEL) at 50 micrograms per cubic meter of air, averaged over an 8 hour shift.
Which of the following grades is not ordinary concrete?
Hence, M40 grade of concrete is not used as ordinary concrete.
What are the advantages of using fly ash in concrete?
Fly Ash has very small particles which makes the concrete highly dense and reduces the permeability of concrete. It can add greater strength to the building. The concrete mixture generates a very low heat of hydration which prevents thermal cracking. Fly Ash concrete is resistant to acid and sulphate attacks.
Which is the main ingredient in cement?
The composition of cement is GaO (lime) or limestone 62% silica (SiO2) 22% alumina (Al2O2) 7.5%, magnesia (MgO) 2.5 % etc. thus, limestone is the major raw material for cement.
Which ingredient gives colour to the cement?
Iron oxide is present about 0.5 – 6.0 % in cement, which provides colour, hardness and strength to the cement.
Who invented cement?
The invention of portland cement usually is attributed to Joseph Aspdin of Leeds, Yorkshire, England, who in 1824 took out a patent for a material that was produced from a synthetic mixture of limestone and clay.
Why is micro silica used?
Used as an admixture, microsilica can improve the properties of both fresh and hardened concrete. Microsilica reduces the rate of carbonation, decreases permeability to chloride ions, imparts high electrical resistivity, and has little effect on oxygen transport.
Is micro silica waterproof?
4.4 Silica Fume Waterproof Concrete Because of its low permeability, micro-silica can be use as an integral water-proofer for below ground structures where some dampness is acceptable, eg Car parks.
Which is a property of micro silica?
Properties of Microsilica Microsilica is a grey; nearly white to nearly black powder. Spherical particles less than 1mm in diameter. The bulk density of is based on the degree of densification and varies from 130 to 600 kg/m3.
Why do we use silica fume in concrete?
Silica fume is added to Portland cement concrete to improve its properties, in particular its compressive strength, bond strength, and abrasion resistance. Silica fume also blocks the pores in the fresh concrete so water within the concrete is not allowed to come to the surface.
What are the advantages of micro silica concrete?
Several materials have recently been used for the improvement of concrete properties. Microsilica or silica fume is an excellent admixture for concrete as it leads to better engineering properties. It reduces thermal cracking, improves durability, and increases strength.
Is silica a cement?
Many common construction materials contain silica including, for example, asphalt, brick, cement, concrete, drywall, grout, mortar, stone, sand, and tile.
What are the disadvantages of high silica cement?
disadvantages of silica fume in concrete Silica fume concrete is too viscous and difficult to apply.it is not easy to wipe the surface. Silica fume requires a high amount of water and needs to be used with a superplasticizer. The price of silica fume is relatively high compared to cement and fly ash.
What is the role of alumina in cement?
Alumina: It imparts quick setting property to the cement. It acts as a flux and lowers the clinkering temperature. Alumina in excess quantity reduces the setting time of cement but simultaneously reduces the strength of cement.
What is the difference between fly ash and silica fume?
Silica Fume is typically much more reactive, particularly at early ages , because of its higher silicon dioxide content and because of its very small particle size. Disadvantages of Fly Ash: – High-carbon fly ash materials tend to use more water and darken the concrete as well.
Is silica fume expensive?
Condensed silica fume costs from $400-$1,000/ton, which is significantly higher than portland cement ($90/ton).
How is micro silica made?
Silica fume, also known as microsilica, is an extremely fine noncrystalline polymorph of silica and is produced in electric arc furnaces (EAFs) as a by-product of silicon and ferrosilicon alloy production. As just mentioned, silica fume arises as a by-product of silicon or ferrosilicon alloy formation in an EAF.
Is silica fume toxic?
Repeated exposure can damage the eyes. * High exposure to Silica, Amorphous (Fume) can cause a flu-like illness with headache, fever, chills, aches, chest tightness and cough. * Repeated exposure to Silica, Amorphous (Fume) can cause lung damage (fibrosis).
How do you mix silica fume in concrete?
(1) Put in aggregate, then put in silica fume, cement and dry mix, then add water and other additives. (2) Put in coarse aggregate + 75% water + silica fume + 50% fine aggregate, stir for 15-30 seconds, then put in cement + concrete admixture + 50% fine aggregate + 25% water, and stir until uniform.
Does silica increase strength?
Silica fume has been successfully used to produce very high-strength, low-permeability, and chemically resistant concrete. Addition of silica fume by itself, with other factors being constant, increases the concrete strength.
How does silica fume work?
When silica fume is added to concrete, initially it remains inert. Its small particle size which is 100 times finer than ordinary portland cement complements the finess modulus of concrete and provides a ball-bearing effect, which improves thixotropic behavior, in effect modifying concrete viscosity.
What is the disadvantage of silica?
Disadvantages of Silica Fume/Micro Silica In case the external temperature is high, it will lead to early dry shrinkage. Hence, it is more prone to cracks which may ultimately affect the overall strength. The construction with the silica fume concrete is difficult; as workability of silica fume concrete is poor.
What is the meaning of pozzolanic?
: finely divided siliceous or siliceous and aluminous material that reacts chemically with slaked lime at ordinary temperature and in the presence of moisture to form a strong slow-hardening cement.
Why lime is used in cement?
Lime provides high water retention that allows for maximum early curing of the cementitious materials. High initial flow which permits easy complete coverage of masonry units. The low air content of cement-lime mortar increases bond strength.
Why is silica bad for you?
Breathing in very small (“respirable”) crystalline silica particles, causes multiple diseases, including silicosis, an incurable lung disease that leads to disability and death. Respirable crystalline silica also causes lung cancer, chronic obstructive pulmonary disease (COPD), and kidney disease.
Is silica safe to take?
According to the United States Department of Labor, about 2.3 million people in the U.S. are exposed to silica at work. As long as you aren’t inhaling silica in its crystalline form, it appears to be safe to consume at the levels set out by the FDA.
How much silica does it take to get silicosis?
Because silicosis is caused by cumulative or repeated exposure to respirable crystalline silica, it makes sense that we would want to limit exposure as much as possible! OSHA has set the Personal Exposure Limit (PEL) at 50 micrograms per cubic meter of air, averaged over an 8 hour shift.
Which of the following grades is not ordinary concrete?
Hence, M40 grade of concrete is not used as ordinary concrete.
What are the advantages of using fly ash in concrete?
Fly Ash has very small particles which makes the concrete highly dense and reduces the permeability of concrete. It can add greater strength to the building. The concrete mixture generates a very low heat of hydration which prevents thermal cracking. Fly Ash concrete is resistant to acid and sulphate attacks.
