Microsilica (also called "silica fume", or "silica fume") is amorphous and powdery silicon dioxide (SiO2) collected by specially designed dust collector after the oxidation of silicon steam discharged from flue during smelting ferrosilicon and industrial silicon. The average particle size of micro-silicon powder is 0.1-0.15 μ M (micron), which is one hundredth of the average particle size of cement. The specific surface area is 15 - 27 m2/g, which has extremely strong surface activity.
Product application: high-strength concrete, amorphous refractory, dry-mixed (ready-mixed) mortar, high-strength non-shrinkage grouting material, wear-resistant industrial floor, repair mortar, polymer mortar, thermal insulation mortar, impermeable concrete, self-leveling concrete, concrete compactor, concrete preservative, cement-based polymer waterproof agent; Reinforcement of rubber, plastic, unsaturated polyester, paint, coating and other polymer materials, modification of ceramic products, etc.
Action principle: micro silica powder/silica fume micro silica powder can be well filled in the cement particle gap after being mixed into the cement concrete, making the slurry slightly denser. In addition, it also combines with free Ca (OH) to form a stable calcium silicate hydrate 2CaO.SiO2.H2O, the strength of the hydrate gel is higher than that of the Ca (OH) crystal.
Performance characteristics: adding appropriate amount of micro-silicon powder into cement products and concrete admixtures can significantly improve the compressive, flexural, impermeable, anti-corrosion, impact resistance and wear resistance at various stages, significantly prolong the service life and significantly improve the product strength. The main performance is:
1) Increase strength. The compressive strength and flexural strength of concrete are greatly increased. When 5-10% micro-silica powder is added, the compressive strength can be increased by 10-30% and the flexural strength can be increased by more than 10%.
2) Increase the density. The impermeability is increased by 5-18 times, and the chemical resistance is increased by more than 4 times.
3) Frost resistance: after 300-500 cycles of rapid freeze-thaw, the relative elastic modulus of micro-silicon powder is 10-20% lower, while that of ordinary concrete is 30-73% lower after 25-50 cycles.
4) Early strength: micro-silica powder concrete can shorten the induction period and has the characteristics of early strength.
5) Abrasion resistance and cavitation erosion control: the abrasion resistance of micro-silicon powder concrete is 0.5-2.5 times higher than that of ordinary concrete, and the cavitation erosion resistance is 3-16 times higher.
Specific application scope
1. Additives for refractories
China is the largest consumer of refractories in the world. The application technology of Sanyuan micro-silicon powder in refractories is relatively mature. Especially, high-quality micro-silicon powder has the characteristics of high fluidity, low water storage, high density and high strength. It is mainly used as high-performance refractory castables, prefabricated parts, ladle materials, breathable bricks, self-flowing refractory castables and dry-wet spraying materials. And oxide bonded silicon carbide products, high-temperature calcium silicate lightweight thermal insulation materials, corundum mullite push plates for electromagnetic kilns, high-temperature wear-resistant materials and products, corundum and ceramic products, etc.
2. For high-strength concrete admixture
Concrete industry is a field with the earliest research, the most achievements and the widest application in the comprehensive utilization of micro-silicon powder abroad. Due to the physical and chemical characteristics of micro-silicon powder, such as fine particles, large specific surface area, high purity of SiO2, strong pozzolanic activity, etc., adding micro-silicon powder into concrete as an admixture can improve the performance of concrete in many aspects, such as significantly improving the adhesion and cohesiveness of plastic concrete, significantly reducing the amount of rebound, increasing the one-time forming thickness of sprayed concrete, shortening the construction period, and saving project costs. In the field of ordinary high-performance concrete and ultra-high-performance reactive powder concrete, micro-silicon powder is used as an admixture to prepare high-strength concrete, and its strength grade can reach more than 100 MPa. Such as RPC concrete, HPC concrete, pipe pile concrete, etc.
3. Admixtures for mixed cement
In 1982, the mixed cement produced by Lafarge Cement Company of France with micro-silicon powder mixed in Portland clinker has entered the market. Generally, the spherical micro-silicon powder is grinded together with clinker to produce mixed cement containing about 6% micro-silicon powder. At present, in some special fields of cement in China, micro-silicon powder has been widely added to make mixed cement or special cement.
4. Main materials of STP hollow insulation board for external wall insulation
The silica fume (and other auxiliary materials) shall be sealed according to the shape of the wall material with a certain size and area by using the characteristics of Sanyuan's silica fume initial product, such as low density, low moisture, dry, fine fineness and good adhesion. After sealing, it shall be compressed and pumped into a hollow. As an inorganic nonmetallic material, silica fume has a very low thermal conductivity. The hollow insulation board made of silica fume has the characteristics of lighter, more energy-saving and thermal insulation.
5. Common additives such as mortar, grouting agent and grouting material
Wall energy conservation, thermal insulation and fire prevention are hot spots in the industry in recent years. Therefore, thermal insulation mortar, foam concrete board and aerated concrete all stand out. Silica fume is also clearly reflected in the application of these products in terms of improving strength and fluidity. At the same time, with the rapid development of high-speed railway technology and construction needs in recent years, through the improvement of grouting material technology, using cement+fly ash+silica fume+cellulose+defoaming agent+water reducing agent+expansion agent, we have developed a super-autogenous, high-strength and dense duct grouting agent. This technology has become increasingly mature and has been widely used in the fields of highways, bridges and high-speed railways.
6. Fertilizer industry
The slow-release agricultural fertilizer potassium silicate can be made by mixing and heating the micro-silicon powder with potassium hydroxide or potassium carbonate. It is not easy to volatilize and lose, can protect the soil, promote the development of crop roots, inhibit diseases and insect pests, and can form a mixture of micro-silicon powder and waste bark produced by cellulose plants or wood plants after processing, which can enhance the fertility of the soil and improve soil varieties.
Precautions for construction of micro-silicon powder
1) Due to the small particle size, large specific surface area and high water demand of micro-silicon powder, it must be combined with high-efficiency water-reducing agent to achieve good results when adding micro-silicon powder into concrete.
2) There are two methods of adding micro-silica powder into concrete: internal mixing method and external mixing method. Because the internal mixing method needs to reduce the amount of cement, this method is generally used in medium and low grade concrete; The external mixing method does not reduce the amount of cement, and is generally used in high-grade concrete.
3) The content of micro-silica powder in concrete should not be too high or too low, and the general content is 5%~10%. Within this range, the beneficial effect of micro-silica powder is best, that is, not only the role of micro-silica powder in replacing cement is best, all kinds of excellent properties are fully played, but also adverse effects can be avoided, such as the frost resistance of concrete is reduced after the content is more than 15%.
4) Anti-permeability concrete, sea-water-resistant concrete, wear-resistant concrete, mixed with micro-silicon powder, will increase water consumption by about 20%, and the strength will not change.
5) Due to the high consistency of micro-silica powder concrete, the slump of concrete should be 2~3cm larger than that of ordinary concrete.
6) The mixing time of micro-silica powder concrete shall be 0.5~2 min longer than that of ordinary concrete, so as to make the concrete mix more evenly and prevent the micro-silica powder from agglomerating in the concrete and causing quality accidents.
7) Secondary plastering and pressing: the concrete shall be plastered and pressed twice before final setting. It is better to cover the concrete after plastering and pressing to avoid surface cracks caused by rapid evaporation of water.
8) Moisturizing maintenance: the concrete shall be moisturized and maintained for more than 14 days in a humid environment from 2 hours to 4 hours after the final setting. The curing method can be watering, covering, or water storage.
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