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Silica fume is a by-product of producing silicon metal or ferrosilicon alloys in smelters using electric arc furnaces. These metals are used in many industrial applications to include aluminum and steel production, computer chip fabrication, and production of silicones, which are widely used in lubricants and sealants.
Fresh concrete made with silica fume is more cohesive and therefore less prone to segregation than concrete without silica fume. Too offset this increased cohesion when placing, silica fume concrete is typically placed at 40 to 55 mm greater slump than concrete without silica fume in the same placement.
Also, because of the very high surface area of the silica fume and the usually very low water content of silica fume concrete, there will be very little, if any, bleeding. Once silica fume content of about 5% is reached, there will be no bleeding in most concretes.
In addition to improved durability, the lack of bleeding allows a more efficient finishing process to be used with silica fume concrete flatwork.
Advantages of silica fume in concrete:
1, micro silica fume powder is a neutral inorganic filler with very stable physical properties and chemical properties. It does not contain crystal water and does not participate in curing reaction, and does not affect the reaction mechanism.
2. It has good wettability to all kinds of resins, good adsorption properties, easy mixing and no agglomeration.
3, the size distribution of micro silica fume is reasonable, strong dense, hardness and wear resistance. It can greatly improve the tensile strength, compressive strength, impact strength and wear resistance of the cured products, and the abrasion resistance can be increased by 0.5 to 2.5 times.
4, it can increase the thermal conductivity, change the adhesive viscosity and increase the flame retardancy.
5, it can reduce the exothermic peak temperature of curing reaction of epoxy resin, reduce the linear expansion coefficient and shrinkage rate of solidified products, thereby eliminating internal stress and preventing cracking.
6. Due to the fine grain size and reasonable distribution of the microsilica, it can effectively reduce and eliminate precipitation and stratification.
7. The microsilica fume is pure, the impurity content is low, the physicochemical property is stable, which makes the curing material have good insulation property and anti arc property.
8, the chemical composition of silica fume is silica (SiO2), which belongs to inert material. It has no chemical reaction with most acids and alkaloids. Microsilica is evenly distributed and covered on the surface of objects. It has strong corrosion resistance and cavitation resistance increased by 3 to 16 times.
9, small packing density: one is in 0.2-0.8, one is between 1.0-2.2. As polymer filling material, it can reduce the cost by reducing the amount of loading and saving the amount of polymer.
10, frost resistance: after 300 to 500 cycles of rapid freezing and thawing, the relative elastic modulus of micro silica powder is 10 to 20%, while that of ordinary concrete is 25 to 50 cycles, and the relative elastic modulus is 30 to 73%. Therefore, the frost resistance of concrete can be improved.
11, early strength: silica fume concrete makes the induction period shorten and has the characteristics of early strength.
Silica fume is a co-product of silicon or ferrosilicon production, consisting of ultrafine (sub-micron), amorphous, non-porous, perfectly spherical silicon dioxide (SiO2) particles, with purity levels of 85&#;99%.
The main effect of these ultra-fine particles is to greatly improve particle packing and produce a highly pozzolanic reaction in concrete and other cementitious bond systems where the silicon dioxide reacts with calcium hydroxide, heightening performance levels and the strength and durability of these materials.
Additionally, silica fume, because of its amorphous (non-crystalline) structure and its high specific surface area, provides other useful features to various applications, including improved sintering capabilities and enhanced high-temperature performance of refractory castables, resulting in reactions between microsilica and other components of the refractory mix.
To summarize, silica fume has two key features which alone or in combination are the basis for its high performance:
Applications are very numerous, including uses in construction, well drilling & cementing, refractories, polymers, etc. This versatility also explains why silica fume is referred to by different names in different industries, such as condensed silica fume or microsilica, the latter used, for example, in high-performance materials (HPM) in the construction and refractory industries.
Elkem markets its wide range of silica fume products under the brand name of MICROSILICA®.
In construction, the Elkem MICROSILICA® line of products improves the performance of a wide range of materials in a variety of applications:
ELKEM MICROSILICA® for high performance concrete
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High-performance concrete with microsilica reduces construction time and provides structural advantages and durability for buildings, bridges, transport tunnels, roadways, etc.
Fiber cement with microsilica is used in roofing materials, such as flat and corrugated sheets, tiles, pipes and moldings for new structures or to efficiently help replace asbestos.
For refractory materials, Elkem MICROSILICA® products offer the following advantages:
ELKEM MICROSILICA® 971
The ELKEM MICROSILICA® 971 product, a high quality, purpose-made, low-impurity grade, for versatile applications in refractories, available in densified (D) or undensified (U) form, to be used in advanced refractory products such as self-flowing, low, ultra-low and no-cement castables.
Product data sheet
ELKEM MICROSILICA® 968
The ELKEM MICROSILICA® 968 product, a cost-effective alternative for low cement castables, featuring a controlled and stable chemical composition.
Product data sheet
ELKEM MICROSILICA® HQ
The ELKEM MICROSILICA® HQ product is a cost-effective alternative for low cement castables, with controlled and stable chemical composition, based on low alkalis and higher reactivity.
Product Data Sheet
ELKEM MICROSILICA® 955
The ELKEM MICROSILICA® 955 product, a medium-quality grade silica fume with tight specification limits based on in-process control, resulting in higher silica content and reduced impurities.
Product data sheet
For oilfield cementing operations, Elkem MICROSILICA® products offer essential bonding and mechanical properties.
MICROBLOCK®
The MICROBLOCK® product, a slurrified multifunctional microsilica additive with a high surface area, processed with quality-controlled particle size distribution that limits gas migration and natural fluid-loss, and improves cement bonding and mechanical properties.
Product data sheet
MICROLITE® P
The MICROLITE® P product, a dry microsilica that creates extra binder phases resulting in lower set-cement permeability and cement slurry density, while maintaining required compressive strength, fluid loss and corrosion resistance in lightweight cement systems.
Product data sheet
MICROLITE® L
The MICROLITE® L product, a pozzolanic slurry with high surface area, which like its powder version enhances compressive strength, lowers permeability, fluid loss and viscosity, resulting in early strength development, strong bonding, and corrosion resistance.
Product data sheet
Elkem also offers complementary materials such as specialty weighting agents, free-flow products designed for easy mixing, and excellent dispersion, flexible components or fibers customized to deal with well stresses etc. The choice between these closely related products is based on specific applications.
Elkem MICROSILICA® products are carefully and accurately processed to ensure key quality parameters, with a careful choice of raw materials (low alkalis, low volatiles), constant quality control, thanks to the application of our rigorous Statistical Process Control System (SPC). This ongoing quality assurance program includes continuous in-process monitoring and analysis of our production, stable charges and adjustments in furnace conditions and post-control of finished products.
This results, among other things, in:
At the application stage, customers are then fully supported by experienced Elkem industry specialists to get the results they require in their very competitive businesses. Our highly competent staff provide full customer services, technical assistance, product development advice and support.
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