Once a nuisance waste product, silica fume is now a valuable addition to cement, creating concrete that is high strength, such as that used to build 311 South Wacker Drive, Chicago, once the world&#;s tallest reinforced-concrete building.
For more information, please visit Silica Fume for Refractories.
Silica fume is a by-product of the silicon metal/ferrosilicon alloy industry. Collected in baghouse filters, it is a very fine pozzolanic material. The addition of silica fume to concrete was first tested in Norway in the s. Although positive results were recorded in terms of improved strength, at that time no method of retaining large quantities of silica fume was available, preventing its industrial-scale use.
This changed in the s, when environmental regulations that required the removal of silica fume from exhaust gases were introduced. This led to significant improvements in filtration technology and, for the first time, the production of large amounts of silica fume.
Building on the earlier work of the s, intensive research was undertaken by Norwegian smelting companies to promote the use of silica fume. This work forms the basis for its use in concrete today.
The advantages of silica fume include significantly increasing concrete strength, a reduction in concrete bleeding and segregation (although this increases the need for proper curing), improved resistance to chemically-aggressive environments, and inhibition of alkali-silica reactions, which can severely damage concrete structures.
It is however a costly and difficult-to-handle material that requires special transportation and dosing equipment to avoid dust formation. It may also reduce resistance to carbonation, raising the risk of corrosion to carbon (black) steel reinforcement.
The very fine nature of silica fume particles (and thus its high surface area) brings both advantages and challenges. It develops strength far more quickly than other pozzolanic materials, allowing its use in the precast industry; however, it also results in a need for significantly more water in concrete production and the use of water-reducing admixtures.
For these reasons, cements containing silica fume are more rarely produced than those containing other pozzolanic industrial by-products, such as fly ash or natural pozzolans, its use being restricted to high-strength applications. For example, high-strength silica fume concrete was used in one of the world&#;s tallest reinforced-concrete buildings, 311 South Wacker Drive in Chicago, helping to significantly reduce the quantity of concrete and reinforcing steel that was required for construction.
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
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
Contact us to discuss your requirements of 95% Densified Silica Fume. Our experienced sales team can help you identify the options that best suit your needs.
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.
To learn more about our sustainability initiatives, check our webpage.
Read more about this topic
Get the best out of Elkem's silica fume (microsilica) by using our software to optimize your mixture
Are you interested in learning more about 85% Densified Silica Fume? Contact us today to secure an expert consultation!
Download EMMA