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Silica fume consists primarily of amorphous (non-crystalline) silicon dioxide(SiO2). Concrete containing silica fume can have very high strength and can be very durable. Micro Silica Fume or Microsilica is finer particle than Cement. It is produced by some chemical processing of the ash.
Is silica fume the same as microsilica?
Silica fume, also known as microsilica, is a fine-grain, thin, and very high surface area silica. The particle size of silica fume is around 1/100th the size of an average cement particle.
What is the difference between densified and Undensified silica fume?
Both undensified and densified silica fumes have particular weight sizes. And you can detect the difference by simply weighing both silica fumes. The weight size for densified or compacted silica fume is generally between 550-650KG/m3. On the other hand, the weight of undensified silica fume is between 250-350KG/m3.
What is the use of microsilica in concrete?
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. Silica fume concrete has a number of construction applications.
What are the important differences between silica fume and Class F fly ash?
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: – Poor-quality fly ash can have a negative effect on concrete (increase permeability ).
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).
What is silica fume used for?
Silica fume, a by-product of the ferrosilicon industry, is a highly pozzolanic material that is used to enhance mechanical and durability properties of concrete. It may be added directly to concrete as an individual ingredient or in a blend of portland cement and silica fume.
What is densified silica fume?
Densified Silica Fume (DSF) (9994039) is a ready-to-use dry densified silica fume used to produce very durable, high strength concrete with very low permeability and low rebound shotcrete. Used For: DSF is recommended for use whenever high-performance concrete or shotcrete is required.
What is Undensified silica fume?
Silica Fume (Undensified) is a by-product of the production of silicon metal. It is a pozzolanic material used to improve the strength of cements. Reacting with the hydration products of portland cement, it forms a calcium silicate hydrate matrix which yields a light weight high compressive strength cement.
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.
How does microsilica improve concrete?
Used as an admixture, microsilica can improve the properties of both fresh and hardened concrete. Because the microsilica particles are so small they disperse among and separate the cement particles. The resulting fine, uniform matrix can give markedly higher compressive, flexural, and bond strength.
How does silica fume effect 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.
Why fly ash is used in cement?
Fly ash is a pozzolan, a substance containing aluminous and siliceous material that forms cement in the presence of water. When used in concrete mixes, fly ash improves the strength and segregation of the concrete and makes it easier to pump.
Why is there no fly ash in concrete?
Poor-quality fly ash can have a negative effect on concrete. The principle advantage of fly ash is reduced permeability at a low cost, but fly ash of poor quality can actually increase permeability. Some fly ash, such as that produced in a power plant, is compatible with concrete.
Can fly ash replace cement?
The replacement of cement by fly ash reduces the water demand for a given slump. Some fly ash is known to reduce drying shrinkage in certain situations. Reduced heat of hydration. Replacing cement with the same amount of fly ash can reduce the heat of hydration of concrete.
Is silica safe to eat?
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.
Is silica a carcinogen?
Silica, Crystalline (Respirable Size). NTP classification: Known to be a human carcinogen. International Agency for Research on Cancer (IARC) Monographs on the Evaluation of Carcinogenic Risks for Humans.
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.
Is silica still used in concrete?
Crystalline silica is a common mineral found in the earth’s crust. Materials like sand, stone, concrete, and mortar contain crystalline silica. It is also used to make products such as glass, pottery, ceramics, bricks, and artificial stone. About 2.3 million people in the U.S. are exposed to silica at work.
What is silica fume and how is it produced?
Silica fume is a by-product from the production of elemental silicon or alloys containing silicon in electric arc furnaces. At a temperature of approximately 2000°C the reduction of high-purity quartz to silicon produces silicon dioxide vapor, which oxidizes and condenses at low temperatures to produce silica fume.
Is silica fume expensive?
Condensed silica fume costs from $400-$1,000/ton, which is significantly higher than portland cement ($90/ton).
