Microsilica (= Silica fume) is a byproduct of producing silicon metal or ferrosilicon alloys. Silicon metal and alloys are produced in electric furnaces. The raw materials are quartz, coal, and woodchips. The smoke that results from furnace operation is collected and sold as silica fume, rather than being landfilled. Perhaps the most important use of this material is as a mineral admixture in concrete. Silica fume consists primarily of amorphous (non-crystalline) silicon dioxide (SiO2). The individual particles are extremely small, approximately 1/100th the size of an average cement particle. Because of its fine particles, large surface area, and the high SiO2 content, silica fume is a very reactive pozzolan when used in concrete. The quality of silica fume is specified by ASTM C 1240 and AASHTO M 307. Microsilica (silica fume) is an amorphous silicon dioxide – SiO2 which is generated as a gas in submerged electrical arc furnaces during the reduction of very pure quartz. As the molten metal is produced, a silica-based gas is emitted. This gaseous fume, as it rises, cools rapidly and forms extremely fine and minute, Amorphous, spherical particles. The microsilica is collected in a bag house, a system for filtering the hot air and gases vented from the furnace. This gas vapor is condensed in bag house collectors as very fine powder of spherical particles that average 0.1 to 0.3 microns in diameter with a surface area of 17 to 30 m2/g.

a) In Elastomers / Polymers: Used as a filler in rubber or plastic. b) Fertilizer: Used in defluorination process during the production of dicalcium phosphate (animal feed). c) Oil & Gas Wells: Used in down hole grouting operations, improves flow (lightweight) and decreases permeability. d) Fiber Cement: Used to improve strength and permeability of corrugated roofing panels. e) Shotcrete – is sprayed concrete: Silica Fume reduces rebound & increases bonding strength, productivity and savings in material cost.

As a new material, Microsilica (that is in powder form) is widely used in the refractory industry. It has an important effect on the improvement of the amorphous refractory. The practical application is in the following aspects: 1. Instead of pure aluminum oxide as refractories. 2. The production of amorphous and shaped refractory products as additives makes the strength and high temperature performance greatly improved. 3. The overall casting ladle coagulant. 4. Other cohesive agents, binders, coagulants and additives for other refractory products

The micro silica (Silica fume) powder can be well filled in the cement particle space and make the slurry more dense, mainly in the following: 1. Increase strength: The compressive strength and flexural strength of concrete increase greatly, adding 5-10% micro silica fume, the compressive strength can be increased by 10-30%, and the flexural strength will be increased more than 10%. 2. Increase the density: The impermeability is increased by 5-18 times, and the anti-chemical ability is increased by more than 4 times. 3. Frost resistance: After 300-500 rapid freeze-thaw cycles, the relative elastic modulus of micro silica powder decreased by 10-20%, while ordinary concrete decreased to 30-73% through 25-50 cycles. 4. Early strength: micro silica concrete makes the induction period shortened and has the characteristics of early strength. 5. Anti-abrasion and anti-cavitation resistance: punching resistance of micro silicon fume concrete improve 0.5-2.5 times than ordinary concrete, and anti-cavitation ability is improved 3-16 times.

High-strength concrete is a very economical material for carrying vertical loads in high-rise structures. Until a few years ago, 6,000 psi concrete was considered to be high strength. Today, using silica fume, concrete with compressive strength in excess of 15,000 psi can be readily produced. The structure shown at the above right used silica-fume concrete with a specified compressive strength of 12,000 psi in columns reaching from the ground through the 57th story. The greatest cause of concrete deterioration in the US today is corrosion induced by deicing or marine salts. Silica-fume concrete with a low water content is highly resistant to penetration by chloride ions. More and more transportation agencies are using silica fume in their concrete for construction of new bridges or rehabilitation of existing structures. Silica-fume concrete does not just happen. A specifier must make a conscious decision to include it in concrete to achieve desired concrete properties. Assistance in specifying silica-fume concrete for high strength or increased durability can be obtained from the SFA or from major admixture suppliers. Silica fume for use in concrete is available in wet or dry forms. It is usually added during concrete production at a concrete plant. Silica fume concrete has been successfully produced in both central-mix and dry-batch plants. Assistance is readily available on all aspects of handling silica fume and using it to produce consistent, high-quality concrete. Silica-fume concrete should be transported, placed, finished, and cured following the good concreting practices by well-known Institutes. Flatwork containing silica fume concrete generally requires less finishing effort than conventional concrete. To gain the most benefits from using silica fume, the concrete must be cured effectively. Your concrete supplier can provide any necessary assistance concerning construction operations.