Silcrete Densified Micro Silica, also known as silica fume, is a highly reactive pozzolan used to enhance the properties of mortar and concrete. This amorphous silica contains a high SiO2 content, an extremely small particle size, and a large surface area, making it a superior material for improving concrete’s performance. When added to concrete, Micro Silica reacts with calcium hydroxide (Ca(OH)2) formed during the hydration of Portland cement, improving strength and durability. The micro filler effect allows it to fill microscopic voids between cement particles, reducing permeability and enhancing the bond between the paste and aggregate.
Micro Silica, or silica fume, offers multiple advantages for concrete, improving its strength, durability, and overall performance:
Increased Strength: By adding 5–10% micro silica to concrete, it can increase compressive strength by 10–50%, improving both tensile and abrasion resistance.
Improved Durability: Micro Silica enhances concrete's resistance to thermal cracking, corrosion, and other forms of deterioration, extending the lifespan of structures.
Impermeability: Micro Silica reduces permeability, preventing the corrosion of reinforcing steel and increasing the concrete's resistance to water, chemicals, and environmental factors.
Enhanced Cohesion: It reduces segregation and increases cohesion in the concrete mix, leading to a more uniform and stable material.
Water Reduction: Micro Silica requires less water, reducing bleeding and improving the quality of the mix.
Frost Resistance: Concrete mixed with Micro Silica is more resistant to freezing and thawing, making it suitable for harsh climates.
Early Strength: It enhances early-age strength, speeding up construction and reducing curing time.
Reduced Carbonation: The addition of Micro Silica slows down the rate of carbonation, further enhancing durability.
Electrical Resistivity: Micro Silica increases concrete’s electrical resistivity, making it more suitable for specific industrial applications.
Corrosion Resistance: It improves the resistance of concrete to corrosion, increasing the longevity of structures exposed to harsh conditions.
Higher compressive strength by 10-25 %
Reduces the rate of carbonation – increases the durability.
Lower permeability – resistance to penetration of water, chloride & other chemicals
Lower free lime formation - delays ettringite and thaumasite formation
Controls bleeding in fresh concrete
Lower Heat of Hydration, which prevents formation of cracks.
Appearance : Very Fine Powder
Colour : Dark Grey
Odour : Odourless
Mean Particle Size : 25 microns
Retention of 325 mesh : Below 5% (w/w)
SiO2 – Silica : 89 % minimum
Humidity : 1 % maximum
Loss on Ignition at 800°C : 4 % maximum
Pozzolonic Effect : When water is added to cement,
hydration occurs as shown below:
Ordinary Portland Cement (OPC) + H2O → CSH (Calcium silicate hydrate) + Ca(OH)2(Free
lime)
The free lime does not contribute to strength of concrete. When combined with carbon
dioxide, it forms a soluble salt, which leaches through the concrete causing
efflorescence and wear & tear of concrete, a familiar problem. This makes the
concrete more vulnerable to chemical attack and deterioration. When Micro Silica is
added, the following reaction takes place:
Ca(OH)2 + SiO2 → H2O + CSH
This reaction reduces the amount of calcium hydroxide (free lime) in the concrete.
Micro Filler Effect : It is an extremely fine material, with an average diameter much finer than the cement. It gets well distributed in the wet concrete paste, thus blocking the bleed-water channels. It also results in better compaction and thereby higher strength.
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