Silica fume, also known as microsilica powder, also known as silicon powder or silica ultrafine powder, silica micro powder.
Silica fume is an ultrafine silica powder material formed by the rapid oxidation and condensation of SiO2 and Si gases generated by metallurgical electric furnaces at high temperatures above 2000 ℃ with oxygen in the air.
1. Physical and chemical properties of silica fume
1. Silica fume:
The appearance is gray or off white powder, with a fire resistance of>1600 ℃. Bulk density: 200-250 kilograms per cubic meter.
2. Fineness of silica fume:
More than 80% of silica fume has a fineness of less than 1 μ m, with an average particle size ranging from 0.1 to 0.3 μ m and a specific surface area of 20 to 28 m2/g. Its fineness and specific surface area are about 80-100 times that of cement and 50-70 times that of fly ash.
3. Particle morphology and mineral phase structure:
During the formation process of silica fume, due to the effect of surface tension during phase transition, amorphous spherical particles are formed, and the surface is relatively smooth. Some are aggregates of multiple spherical particles stuck together. It is a volcanic ash material with a large specific surface area and high activity. Materials mixed with silica fume, small spherical bodies can provide lubrication.
2、 The effect of silica fume/microsilica powder
Silica fume can fill the pores between cement particles, generate gel with hydration products, and react with alkaline material magnesium oxide to generate gel. Adding an appropriate amount of silica fume to cement-based concrete, mortar, and refractory castables can have the following effects:
1. Significantly improve compressive strength, flexural strength, impermeability, corrosion resistance, impact resistance, and wear resistance.
2. It has the function of retaining water, preventing segregation and bleeding, and significantly reducing the pumping resistance of concrete.
3. Significantly extend the service life of concrete. Especially in harsh environments such as chloride pollution erosion, sulfate erosion, and high humidity, the durability of concrete can be doubled or even multiplied.
4. Significantly reduce the landing ash of sprayed concrete and pouring materials, and increase the thickness of a single spraying layer.
5. It is a necessary component of high-strength concrete and has been applied in engineering with C150 concrete.
6. It has about 5 times the effectiveness of cement and can reduce costs when used in ordinary concrete and low cement castables Improve durability.
7. Effectively prevent the occurrence of concrete alkali aggregate reaction.
8. Improve the density of cast refractory materials. When coexisting with Al2O3, it is easier to generate mullite phase, which enhances its high-temperature strength and thermal vibration resistance.
3、 Scope of application
Commercial concrete, high-strength concrete, self leveling concrete, amorphous refractory materials, dry mixed (pre mixed) mortar, high-strength non shrinkage grouting material, wear-resistant industrial flooring, repair mortar, polymer mortar, insulation mortar, impermeable concrete, concrete compactor, concrete preservative, cement-based polymer waterproofing agent; Reinforcement of rubber, plastic, unsaturated polyester, paint, coatings, and other polymer materials, modification of ceramic products, and so on.
4、 Application Fields
1. Used in mortar and concrete:
High rise buildings, harbor docks, reservoir dams, water conservancy, culverts, railways, highways, bridges, subways, tunnels, airport runways, concrete pavements, and coal mine roadway anchoring and spraying reinforcement.
2. In the materials industry:
(1) High end high-performance low cement refractory castables and prefabricated components have a service life three times that of ordinary castables, with a fire resistance increase of about 100 ℃, and significant improvements in high-temperature strength and thermal shock resistance. It has been widely used in industries such as coke ovens, ironmaking, steelmaking, steel rolling, non-ferrous metals, glass, ceramics, and power generation.
(2) Large scale iron trenches and steel ladle materials, breathable bricks, application and repair materials, etc.
(3) Application of self flowing refractory pouring materials and dry wet spraying construction.
(4) Oxide bonded silicon carbide products (ceramic kiln furniture, flame plates, etc.).
(5) High temperature calcium silicate lightweight insulation material.
(6) Corundum mullite push plates are used for electric porcelain kilns.
(7) High temperature wear-resistant materials and products.
(8)Corundum and ceramic products.
(9) Sailong combination products.
At present, in addition to being widely used in casting refractory materials, it has also been widely applied in electric melting and sintering refractory materials.
3. New wall materials and decorative materials:
(1) Polymer mortar, insulation mortar, and interface agent are used for wall insulation.
(2) Cement based polymer waterproof material.
(3) Lightweight aggregate insulation energy-saving concrete and products.
(4) Processing of putty powder for interior and exterior wall construction.
4. Other uses:
(1) Raw materials for silicate bricks.
(2) Produce water glass.
(3) Used as a reinforcing material for organic compounds. Because its composition is similar to that of white carbon black produced by gas-phase method. It can be used as a filling and reinforcing material in polymer materials such as rubber, resin, coatings, paints, and unsaturated polyester.
(4) Used as an anti caking agent in the fertilizer industry.
5、 Usage and precautions
1. Mixing amount:
Generally, it is 5-10% of the amount of cementitious material. The method of adding silica fume is divided into internal and external blending.
(1) Internal mixing: Under the premise of constant water addition, 1 part of silica powder can replace 3-5 parts of cement (by weight) and maintain the compressive strength of concrete while improving other properties of concrete.
(2) External addition: With the same amount of cement, adding silica fume significantly improves the strength and other properties of concrete. When adding silica fume to concrete, there is a certain degree of slump loss. This should be noted during the mix proportion test.
Silica fume should be used in conjunction with water reducing agents, and it is recommended to add fly ash and ground slag to improve its workability.
When using silica fume to prepare concrete, the weight ratio of silica fume to cementitious material is generally:
（1） High performance concrete: 5-10%;
（2） Hydraulic concrete: 5-10%
（3） Spray concrete: 5-10%;
（4） Pump aid: 2-3%;
（5） Wear resistant industrial flooring: 6-8%;
（6） Polymer mortar and insulation mortar: 10-15%,
（7） Amorphous refractory castable: 6-8%. Before use, please select a reasonable and economical dosage through experiments according to actual needs.
2. Mixing method:
The construction mix proportion of silica fume concrete and castable should be determined by the laboratory. Strictly follow the mix proportion for construction. In the mixing of silica fume concrete, silica fume should be added to the mixer immediately after the aggregate is fed. There are two ways to join:
(1) Add aggregates, then dry mix with silica fume and cement, and add water and other additives.
(2) Add coarse aggregate+75% water+silica fume+50% fine aggregate, stir for 15-30 seconds, then add cement+admixture+50% fine aggregate+25% water, stir evenly. The mixing time is extended by 20-25% or 50-60 seconds compared to ordinary concrete. Do not add silica fume to the mixed concrete.
3. Construction method:
The construction methods of silica fume concrete and ordinary concrete are not significantly different, but it is necessary to organize and compact them well during construction. The early strength performance of silica fume concrete will advance the final setting time, and attention should be paid when plastering; Simultaneously adding silica fume can improve the viscosity of concrete and significantly reduce bleeding, making plastering slightly more difficult.
4. Construction safety:
The construction safety of silica fume concrete should strictly follow the relevant national construction specifications for concrete engineering. However, due to the light weight of silica fume, it is strictly prohibited to throw materials from high altitude to prevent silica fume from flying.
6、 Packaging, storage, and transportation of products
1. This product is packaged in a laminated plastic woven bag.
2. This product should be stored in a dry, sheltered, and shaded environment. The product loses its activity by clumping when exposed to water. Prohibit prolonged exposure to sunlight to prevent packaging bags from weathering and product spillage.
3. This product is not classified as dangerous goods and can be transported in accordance with the Non Dangerous Goods Regulations.
