Concrete is highly heterogeneous and is a material that is in high demand for the construction industry worldwide. An important ingredient involved in making concrete is cement, but excessive use of cement creates a major environmental concern.To overcome this problem and precisely maintain the strength of concrete, it is necessary to look for new supplementary cementitious materials. Therefore, in recent years, researchers have sought to find better alternatives to concrete and have tried to create materials that have properties that can be obtained by adding alternative by-products in construction.Silica fume or microsilica is an important byproduct produced during the production process of ferrosilicon and silicon metal alloys. This compound finds wide applications in concrete and has important benefits for the marine, construction, and oil and gas industries worldwide.
Silica fume is a byproduct of ferrosilicon and silicon. Silica fume is a very fine non-crystalline silica that is obtained in electric arc furnaces as a by-product during the production of elemental silicon or silicon-containing alloys and rises as an oxidized vapor when it cools andcondenses. Silica fume is spherical in shape, this is a very fine particle with a size of less than 1 (micron) and an average diameter of about 0.1 (micron). It is about 100 times smaller than an average cement particle. which is responsible for the compressive strength and durability of concrete.It is primarily silicon dioxide (over 90%) in non-crystalline form. Silica has both pozzolanic properties and cement properties. It is also known as a pozzolanic additive or supplementary cementitious material. Silica fume effectively increases the mechanical properties to a great extent. It is durable and offers good corrosion resistance to embedded steel.
When silica fume is added to concrete, the silica fume is initially ineffective. Then, when the water begins to react (hydrate) with the Portland cement in the mixture, the initial chemical reaction produces two important chemical compounds:• Calcium silicate hydrate (CSH), the crystalline compound responsible for the strength of the material• Calcium hydroxide (CH), a by-product that acts as a filler and lines the pores in concrete.Then, a pozzolanic reaction occurs between the calcium hydroxide and the silica fume, producing additional calcium silicate hydrate compounds that fill the voids around the hydrated cement particles.These additions of CSH to concrete provide a denser matrix in areas that remain exposed to potential infiltration as small voids. In this way, the concrete develops improved flexural, compressive and bond strength properties.
1.Physical state: gel
2.Color: Gray
3.pH: 10
4.Packaging: 25 kg gallon
5.Expiry date: 8 months after production in a sealed 6.bag away from moisture
7.Mixing ability: Yes
8.Chlorine ion: No
9.Freezing point: 2-
Microsilica fume gel significantly enhances the compressive strength, flexural strength, and tensile strength of concrete. The refined microstructure and denser matrix resulting from pozzolanic action contribute to this enhanced strength. Additionally, microsilica fume gel improves concrete’s resistance to chemical attack, sulfate attack, and abrasion, ensuring long-lasting durability.
The dense microstructure induced by microsilica fume gel significantly reduces concrete’s permeability, minimizing the passage of water and harmful substances. This enhanced water resistance protects reinforcing steel from corrosion, extending the lifespan of concrete structures.
Microsilica fume gel acts as a dispersing agent, effectively dispersing cement particles and reducing friction between them. This enhanced dispersion improves concrete’s workability, making it easier to mix, place, and finish, particularly in applications requiring high flowability.
The refined microstructure and reduced permeability resulting from microsilica fume gel minimize concrete shrinkage and cracking. This reduction in cracking potential enhances the structural integrity and aesthetics of concrete elements.
Microsilica fume gel, as a by-product of the silicon metal and ferrosilicon alloy industries, promotes sustainable construction practices by utilizing waste materials. Additionally, its use reduces the need for traditional cement, lowering greenhouse gas emissions associated with cement production.
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While microsilica undoubtedly offers a wide range of benefits when added to concrete, it also comes with certain disadvantages:
Concrete workability is an important parameter to consider in designing proportions for a particular concrete mix. For example, adding excessive amounts of silica fume powder reduces the workability of the material and causes the concrete to compress. Plastering of concrete or its granulation will be more difficult and will negatively affect the quality of concrete, smoothness and uniformity of the surface.
Compared with ordinary concrete, the shrinkage rate of silica fume concrete, especially the initial dry shrinkage, is significantly higher. This can be explained by the fact that the filling effect of silica fume leads to a decrease in the moisture content of concrete, which in turn leads to dry shrinkage cracks. This affects the overall strength of the product and limits potential applications.
In addition, when the outdoor temperature is high, surface water evaporation increases beyond the bleeding rate, causing dry shrinkage cracks to appear on the surface. Fortunately, this problem can be mitigated by focusing on the maintenance of concrete after construction, such as using water-strengthening methods and sprinklers.
Microsilica concrete is also more likely to develop thermal cracks. While the initial strength is quickly established by the addition of silica fume powder, the corresponding heat of hydration of the concrete is quickly dissipated, leading to an increase in the temperature of the concrete.
This, in turn, exerts high temperature stress on the material, which is concentrated above the dry shrinkage cracks. This can deepen these cracks and lead to the formation of transmission cracks.
The price of microsilica is relatively high compared to fly ash or cement. While the use of silica fume increases initial costs, the better performance of silica foam cement will offset the costs in the long run.
Microsilica fume gel consists of extremely small, amorphous silica (SiO2) particles, known as microsilica fume, suspended in a liquid carrier, typically water or an aqueous solution. These particles, with an average diameter of around 0.15 micrometers, exhibit exceptional pozzolanic properties, meaning they react with calcium hydroxide (CH) produced during cement hydration to form additional calcium silicate hydrate (C-S-H) gel. This reaction, known as pozzolanic action, refines the concrete microstructure, leading to enhanced strength, durability, and workability.
Microsilica fume gel finds extensive applications in various concrete structures and elements, including:
High-Performance Concrete (HPC): Microsilica fume gel is a crucial ingredient in HPC, where its strength-enhancing and durability-improving properties are essential for demanding applications such as skyscrapers, bridges, and offshore structures.
Self-Compacting Concrete (SCC): The enhanced workability and flowability imparted by microsilica fume gel make it an ideal additive for SCC, enabling self-compaction without the need for external vibration, particularly in congested reinforcement areas.
Repair and Rehabilitation Mortars: Microsilica fume gel’s strength-enhancing and adhesion-promoting properties make it valuable for repair and rehabilitation mortars, ensuring strong bonding with existing concrete and restoring structural integrity.
Precast and Prestressed Concrete: The high strength and durability of microsilica fume gel-modified concrete are particularly beneficial for precast and prestressed concrete elements, where dimensional stability and long-term performance are critical.
Grout and Sealants: Microsilica fume gel’s ability to fill voids and microcracks effectively makes it a suitable additive for grout and sealants, enhancing their filling capacity and sealing performance.
Compatibility with Cement: Ensure compatibility between the microsilica fume gel and the specific cement type being used to optimize the pozzolanic reaction and achieve desired performance.
Dosage Optimization: Determine the appropriate dosage of microsilica fume gel based on the desired concrete properties, application requirements, and specific project conditions.
Mixing and Application: Follow recommended mixing procedures and application techniques to ensure proper dispersion of microsilica fume gel and achieve the desired benefits.
Curing Regimen: Implement a proper curing regimen to optimize hydration and strength development of concrete containing microsilica fume gel.
Microsilica fume gel has revolutionized concrete technology, offering a range of performance benefits that make it a valuable addition to modern construction practices. Its ability to enhance strength, durability, workability, and environmental sustainability has propelled its use in diverse applications, from high-rise structures to repair and rehabilitation projects. As the construction industry continues to seek innovative and sustainable solutions, microsilica fume gel is poised to play an increasingly significant role in shaping the future of concrete technology.
