Microsilica powder is also called silica fume or condensed silica fume. When ferro alloy is smelting ferro silicon and industrial silicon (silicon metal), a large number of highly volatile SiO2 and Si gases are produced in the mineral-thermal electric furnace, and the gas is rapidly oxidized and condensed with the air after discharge. Micro-silicon powder is a by-product in large industrial smelting, the whole process needs to be recycled with dust removal environmental protection equipment, because the quality is relatively light, but also need to be encrypted with encryption equipment.
Physical properties of micro-silica powder
(1) Color: micro-silica powder is the by-product of the reduction of high-purity quartz, coke and wood chips in the ore furnace during the production of ferro silicon or silicon metal, the main component is SiO2, the general color of micro-silica powder is between light gray and dark gray, SiO2 itself is colorless, its color mainly depends on the content of carbon and iron oxide, the higher the carbon content, the darker the color; In addition, the encrypted silicon powder is darker than the natural silicon powder.
(2) Particle size: The average particle size of micro-silica powder is about 0.15~0.20μm (micron), which is 1/100 of the diameter of the cement particle, so the silica powder can be highly dispersed in the concrete, filled between the cement particles and improve the density, while the micro-silica powder has a high activity, and can react faster and more comprehensively with the oxygen and hydrogen compounds produced by the hydration of cement.
(3) Specific surface area: 15000-20000m2/kg
(4) Density of specific gravity: there are two main supply forms of silicon powder, namely, original micro-silicon powder and densified micro-silicon powder.
a, the original micro-silica powder, that is, the product collected directly by the dust collector, the loose volume is about 150-300kg/m3, the original silica powder is generally transported in bags, due to the small density, the long-distance transportation efficiency is low, the use of manual direct bag to break the micro-silica powder into the concrete mixer, the working environment is dusty and the work efficiency is low.
b, densification of micro-silica powder, in order to solve the problem that the original micro-silica powder is not suitable for long-distance transportation and low efficiency, the micro-silica densification technology has been developed to improve the loose density of micro-silica powder. This technology enables the original micro-silica powder to roll and aggregate into small particles under the action of compressed air flow, thus increasing the loose volume of micro-silica powder to 350-700 kg/m3, which is greatly convenient for use. The particle cohesion of the dense micro-silica powder small particles is weak, and it is very easy to disperse during the mixing process in the concrete mixer. Therefore, the micro-silicon powder particles can be put into the mixer after the aggregate is fed to ensure the dispersion and good dispersion of the densified micro-silicon particles.
The role of micro-silicon powder
Physical action:
Because of the fine particles, it fills the pores between the cement particles, makes the slurry denser, improves the microstructure of cement and aggregate, and thus improves the macroscopic physico-mechanical properties (strength, impermeability, durability, elastic modulus, etc.) of the concrete material.
Chemical reaction:
The main component of silicon dioxide (SiO2) in the silicon powder can react with the Ca(OH2) of cement hydration under alkaline excitation conditions to produce a hydraulic silicate colloid – calcium silicate hydrate gel (also known as CSH gel), which greatly improves the concrete compactness. The strength of calcium silicate gel was much higher than that of Ca(OH)2 gel. Therefore, silica powder has the advantages of pozzolanic effect and particle effect, which can improve the moisture and cohesiveness of newly mixed concrete and achieve the purpose of improving the quality of concrete.
1, significantly improve the compression, folding, impermeability, corrosion resistance, impact resistance and wear resistance.
2, with water retention, prevent segregation, bleeding, greatly reduce the role of concrete pumping resistance.
3, significantly extend the service life of concrete. Especially in the chlorine salt pollution erosion, sulfate erosion, high humidity and other harsh environment, the durability of concrete can be doubled or even several times.
4, greatly reduce the ground ash of shotcrete and castable, improve the thickness of a single spray layer.
5, is a necessary component of high-strength concrete, C150 concrete has been applied in engineering.
6, it has about 5 times the effect of cement, and the application in ordinary concrete and low cement castable can reduce the cost. Improve durability.
7, effectively prevent the reaction of concrete alkali aggregate.
8, improve the density of cast refractory. When coexisting with Al2O3, it is easier to generate mullite phase, so that its high temperature strength and thermal vibration resistance are enhanced.
The scope of application of micro-silicon powder:
Micro-silica powder is suitable for commercial concrete, high-strength concrete, self-leveling concrete, amorphous refractory materials, dry mix (ready-mix) mortar, high-strength non-shrinkage grouting material, wear-resistant industrial floor, repair mortar, polymer mortar, thermal insulation mortar, impermeable concrete, concrete compacting agent, concrete preservative, cement-based polymeric waterproof agent; Rubber, plastic, unsaturated polyester, paint, coatings and other polymer materials reinforcement, modification of ceramic products, automotive tire wear modification and so on.
The application field of micro-silicon powder:
1, used in mortar and concrete: high-rise buildings, port pier, reservoir dam, water conservancy, culvert, railway, highway, bridge, subway, tunnel, airport runway, concrete pavement and coal mine roadway anchoring and spraying reinforcement.
2, In the material industry:
(1) High-grade high-performance low-cement refractory castable and prefabricated parts, the service life is three times that of ordinary castable, the refractories are increased by about 100 ° C, and the high temperature strength and thermal shock resistance are significantly improved. Has been widely used in: coke oven, iron, steel, steel rolling, non-ferrous metals, glass, ceramics and power generation and other industries. (2) Large iron groove and ladle material, breathable brick, smear repair material, etc.
(3) Self-flowing refractory castable material and dry and wet spraying construction application.
(4) oxide-bonded silicon carbide products (ceramic kiln, flame shield, etc.).
(5) High temperature calcium silicate light insulation material.
(6) corundum mullite push plate for electric porcelain kiln.
(7) High temperature wear-resistant materials and products.
(8) Corundum and ceramic products.
(9) Cylon combined products. At present, in addition to being widely used in cast refractories, it is also widely used in electric melting and sintering refractories.
3, New wall materials and finishing materials:
(1) Wall insulation with polymer mortar, insulation mortar, interface agent.
(2) cement-based polymer waterproof material.
(3) lightweight aggregate thermal insulation energy-saving concrete and products.
(4) Interior and exterior construction with putty powder processing.
4, Other uses:
(1) silicate brick raw materials.
(2) Production of water glass.
(3) Used as a reinforcing material for organic compounds. Because its composition is similar to the white carbon black produced by gas phase method. It can be used in rubber, resin, paint, paint, unsaturated polyester and other polymer materials as filling and reinforcing materials.
(4) Used as an anti-caking agent in the fertilizer industry.
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The application of micro-silica powder in concrete:
(1) Improve the early strength and final strength of concrete
When the substitution rate of micro-silica powder to cement is less than 30% and the vapor temperature is 80℃, the compressive strength of the mortar is twice that of the slurry without micro-silica powder (100MPa). If no autoclave curing is used, it is nearly 3 times (150MPa); Using standard curing, the compressive strength of mortar is also significantly improved. When the micro-silica powder is combined with high-efficiency alkali water agent, the water-binder ratio (W/C+Si) of concrete can be reduced to 0.13-0.18, the cement particles are packed with silica powder, and the compressive strength of concrete is 3-5 times of that without silica powder.
(2) Increase the density of concrete
The addition of micro-silica powder in concrete increases the content of reactive silica. Under electron microscope, crystal growth is observed in the interstitial space of silica doped concrete. In addition, the micro-silica powder particles are very fine and evenly filled with concrete microholes. According to the method of cement injection abroad, no matter what kind of curing conditions, the micro-pore volume of concrete cement stone doped with micro-silica powder is significantly reduced.
(3) Improve concrete segregation and bleeding performance
After pouring concrete, water is often separated from the concrete, that is, water film is formed on the surface, also known as floating slurry, so that the upper concrete distribution is not uniform, affecting the quality of construction.
