What is Micro Silica Fume?
You may already know that micro silica fume is a by-product of elemental silicon production. But did you know that micro silica fume particles are sphere-shaped and are very fine, with a mean size of only 0.1 to 0.3 micrometers? This property makes them an excellent additive for concrete mixtures. Such small particle sizes facilitate grinding with Portland cement to get blended cement. The contents of micro silica fume mixed concrete typically are cement, silica fume, fine and coarse aggregate, and water.
Micro Silica fume is used as an additive to concrete or as a component in Portland cement. It has shown to increase compressive strength and reduce permeability and shrinkage of the concrete. This means that you can use less concrete to get the same effect with micro silica fume in your mixture. Another use for Micro Silica Fume is in concrete, where the silica fume provides a chemical reaction with the cement paste, which produces heat. This heat production helps to make the concrete easier to handle and build with. Another use for silica fume is as a soil conditioner in agriculture. Because of its fantastic ability to absorb liquid has been used as a replacement for organic fertilizers such as manure, blood meal, and bone ash. This is important because the chemical compounds that make up the organic fertilizers convert to nitrates in water. This can cause problems with surrounding ecosystems and groundwater. Micro silica fume is also used as a flame retardant because it has an amazing ability to absorb liquid and form a protective barrier around itself.
What are the Benefits of Using Silica Fume for Construction?
Before we discuss the use of Micro Silica Fume in construction, let us get to know silica fume better:
- Silica fume contains more than 90% of silicon dioxide.
- The rest of the constituents include carbon, sulfur, aluminum oxides, iron, calcium, sodium, magnesium, and potassium.
- The surface area for silica fume particles is between 13,000 to 30,000 sq meters per kilogram. However, the best-suited, most practical specification is around 15,000 sq meters per kilogram or 15 sq meters per gram.
- Silica fume in the range of 500 to 700 kilograms per cubic meter density is considered ideal for concrete additives.
Now that we know micro silica fume better, let us explore the advantages of adding it to concrete mixes:
- Silica fume makes the concrete mix more efficient and reduces wastage by reducing segregation and bleeding of the mix
- It enhances the properties of fresh and hardened concrete (discussed later in the article)
- Higher concrete durability
- Greater early compressive strength for the mix
- Concrete mixes with added silica fume exhibit a high modulus of elasticity and flexural strength
- Smaller particles attributed to high bond strength
- Silica fume prevents thermally induced cracking, thereby making it suitable for mass concreting purposes
- Ability to prevent most aggressive chemical attacks
Chemical reactions within micro silica fume concrete
Chemical reactions are triggered as soon as the dry mix of Portland cement, and micro silica fume is mixed with water. Two chemical compounds are produced, namely Calcium Hydroxide and Calcium Silicate Hydrate. The first chemical, Calcium Hydrate, is also known as free lime. It facilitates by lining all the existing pores in concrete as a filler. The second chemical, Calcium Silicate Hydrate, is the crystalline compound that provides strength to the mix.
Following the first reaction, a subsequent pozzolanic reaction takes place among calcium hydroxide and silica fume to produce more Calcium Silicate Hydrate compounds. These further fill up the voids around the existing hydrated particles of cement. The formation of such crystal compounds makes the concrete denser by converting bigger voids into smaller ones. Giving out a resultant concrete material that exhibits improved flexural, compressive, and bond strength.
Micro silica fume has proved useful in terms of resistance to freeze-thawing and provides high compressive strength.
Types of silica fume available in market
- As-produced silica fume – This type of silica fume is available in extremely fine powdered form. It has lower bulk density, and its flow depends on the efficiencies of the pneumatic conveying equipment. As the material is tough to handle, it involves higher loading, storage, transportation and dosing costs. It is not a popular choice for construction projects because of the dust it generates while processing.
- Silica fume slurry – A water-based slurry is prepared from the as-produced silica fume, which is easy to transport and use. It contains about 40-60% silica fume.
- Densified silica fume – Also known as compacted silica fume, this type is supplied in the form of dense products that provide similar handling as Portland cement. It is produced by holding as-produced silica fume in silos where compressed air is introduced from the bottom leading to the deposition of dense
- Pelletized silica fume – is prepared by adding small amounts of water and cement to the as-produced silica fume. A disk pelletizer is used to turn the mix into dense pellets.
How to Use Micro Silica Fume in Construction Projects?
Adding silica fume to concrete brings out striking changes in ordinary concrete mixes. They include:
- Improvements in strength
The Calcium Hydroxide crystals produced within the silica fume concrete mix forms the basis for making smaller sized crystals that are more randomly oriented within the mix. Micro silica fume addition improves the bonding strength in cement paste mix. It also facilitates connections among different composite components present in the concrete mix, thereby giving it high-strength. These aggregate particles also reinforce the concrete, thereby playing a much more influential role than being just an filler additive.
A study was conducted where the effect of silica fume on durability of fly ash concrete composites was recorded. The researchers used four different silica fume concentrations (3%, 6%, 9% and 12%). It was observed that the added silica fume positively affects the carbonation resistance, durability of water impermeability, and freeze-thaw resistance. Greater concentrations of silica fume decreased the carbonation depth. Also, adding silica fume has a small impact on the workability and dry shrinkage properties of fly ash containing concrete composites. Silica fume concentrations indirectly correlate with the slump and the slump flow.
- Improvements in frost resistance
Even after 300 to 500 fast freeze-thaw cycles, the relative elastic modulus of silica fume is 10-20%. In contrast, the average elastic modulus of conventional concrete is 30-73% after 25-50 cycles.
- Improvements in filling
It is observed that silica fume concentration of 15% in concrete mix greatly increase strength of the mix. Addition of silica fume greatly reduces size of voids of cement particles. This effect is similar to how cement particles act as fillers between aggregate, coarse aggregate and fine aggregate voids. Such increments in the density and strength of high-strength concrete have a filling effect attributed to silica fume addition.
- Improvement in bleeding
Silica fume particles bring about homogeneity in concrete mixes as they fill the pores. Silica fume presence at the time of transition of the cement slurry and aggregate interface reduces the bleeding of concrete. It does not allow moisture content to accumulate under the aggregate.
When it comes to adding silica fume to the preparation concrete mix, the composition varies depending on the end use and concrete type. Typical concentration varies between 10% to 15% of cementing material. We list the different ratios as follows:
- High-performance concrete: 5-10%
- Hydraulic concrete: 5-10%
- Shotcrete: 5-10%
- Pumping aid: 2-3%
- Wear-resistant industrial floor: 6-8%
- Polymer mortar and thermal insulation mortar: 10-15%
Micro silica fume concrete preparation process:
- Grinding of agglomerations to suitable silica fume particles.
- Mixing of silica fume particles with other concrete constituents in a uniform manner
- Adding water to the dry mix up to 75%
- Addition of coarse aggregates
- Addition of silica fume, followed by cement or fly ash in revolving mixer
- Addition of fine aggregates
- Addition of the remaining 25% water to bring the mix up to desired consistency and workability
Properties of Micro Silica Fume that set it apart from other Construction Materials
Silica fume as an additive to concrete has several advantages. Properties of fresh silica fume concrete include:
- High plastic shrinkage
- Conventional concrete mixtures require relatively less water content to achieve similar workability. The advantages of the addition of silica fume outweigh the extra water content requirements.
- Low workability, as the higher water content is necessary.
- Silica fume concrete tends to have low slump value
- Concrete with added silica fume will exhibit lower instances of bleeding and segregation
- A cohesive mixture with silica fume
Some properties of hardened silica fume concrete that are different from fresh silica fume concrete are:
- Higher compressive strength over ordinary concrete
- Higher modulus of elasticity over ordinary concrete
- Much lesser creep relative to ordinary concrete
The Best Material for Building Projects – Why You Should Use Micro Silica Fume
Let us discuss different use cases for silica fume in construction projects.
- Applications in concrete
The popularly used High Performance Concrete can have silica fume as an additive. Not only does it improve durability and strength, but the HPC also produced using silica fume results in improved resistance to abrasion, higher toughness, resistance to corrosion and chemicals, and economic efficiencies.
Structures like parking decks, highways and highway bridges, and marine structures face constant deterioration due to rebar corrosion, abrasion, and chemical attacks. Silica fume addition protects the concrete structures against regularly applied de-icing salts, traffic, seawater, and natural disasters. Silica fume addition also reduces maintenance costs by eliminating concrete deterioration and rebar corrosion.
- Applications in repair materials
Silica fume finds great to use wherever cement-based repair products are applied. Several applications include vertical and overhead mortars that can have greater adhesion by adding silica fume. It is useful even for underwater grouting that’s to its reduced permeability. It is also useful when exposed to reactive chemicals like sulfates, nitrates, chlorides and acids. The reduced bleeding property helps keep the application both economical and more efficient.
- Applications in refractory as well as ceramics
Sililca fume has a small particle size, making it best suited for refractory castables. Low-temperature sintering is made possible in its presence. It also provides castables resistant to slag, metal, and gas penetration. Such castables stay strong even at high temperatures.
- Applications in shotcrete
Substantial economy and efficiencies are exhibited by shotcrete that has added micro silica fume. Popular applications for silica fume shotcrete include mine tunnel lining, rock stabilizations, and massive maintenance improvements in old bridges and marine columns. Thanks to the smaller particle sizes that help improve bonding strength, silica fume in shotcrete deliver excellent performance for dry and wet shotcrete processes. The reductions in rebound losses measure up to 50%. Silica fume ensures thick application and the least rebound loss at each passage of the shotcrete dispensing nozzle. A single pass of the nozzle can deposit up to 12 inches. Shotcrete made using silica fume has low permeability and high electrical resistivity. Like silica fume concrete, silica fume shotcrete also boasts better flexural and high compressive strength.
- Applications in Oil well grouting
Silica fume provides for dual application use. In the case of the primary application, the grout is placed as a hydraulic sealant in the bored well. For secondary applications, silica fume is used for repairing leaks, splits, and closure of depleted locations. Silica fume is a non-reactive and tightly bonded material. It does not allow gases to pass and improves operational efficiency.
Hence, using micro silica fume in oil well-related applications helps improve flow and decreases permeability. Silica fume is a lightweight option that also has high compressive strength.
Sustainability of silica fume use in construction
The Environmental Protection Agency (EPA) has identified only three sustainable Supplementary Cementitious Materials. They are silica fume, slag cement, and fly ash. EPA named Silica fume one of the Recovered Mineral Components, making it a future-proof material. Not only does micro silica fume extend the life cycle for concrete structures, its addition greatly helps reduce concrete footprint across the globe. Its ability to withstand natural disasters, low maintenance, and inert properties make it the best choice for construction projects.
At Henan Superior Abrasives, we want to make sure that you can find the right product in the shortest amount of time. Our team of knowledgeable and helpful customer service representatives are happy to answer any questions and walk you through the options. Our products are made from high-quality materials, tested by strict quality control standards, and approved by professional laboratories to ensure consistency. This means that what you buy is exactly what you need without any hidden variables that may affect your project.
Henan Superior Abrasives has been providing the best quality abrasives for over 20 years. We manufacture and export micro silica fume and all of our premium products are widely used in abrasives, refractory, technical ceramics, and many other industries.