Micro Silica Concrete
How microsilica improves concrete strength, permeability and durability — with dosage, mix guidance and where it's used.
Micro silica concrete is high-performance concrete in which part of the ordinary Portland cement is replaced with microsilica — an ultra-fine amorphous silicon dioxide (SiO₂) powder produced during silicon and ferrosilicon manufacturing. With particles roughly 100 times finer than cement, micro silica acts both as a highly reactive pozzolan and as a micro-filler, delivering the strength, density and durability required by modern infrastructure.
This guide covers how micro silica works in concrete, the measurable benefits, recommended dosages and the applications where it makes the biggest difference.
How micro silica improves concrete
Higher compressive & flexural strength
Micro silica reacts with calcium hydroxide (Ca(OH)₂) released during cement hydration, producing additional C-S-H gel. This densifies the paste and can raise 28-day compressive strength by 20–40% at typical dosages.
Drastically lower permeability
Ultra-fine (<1 μm) amorphous SiO₂ particles fill the microstructure between cement grains and refine capillary pores, cutting chloride-ion penetration and water permeability by more than half.
Improved durability in aggressive environments
Micro silica concrete resists sulphate attack, alkali-silica reaction (ASR) and chloride-induced corrosion — the leading causes of premature failure in marine, coastal and industrial structures.
Better bond with steel and aggregate
The denser interfacial transition zone (ITZ) improves paste-to-aggregate and paste-to-rebar bond, useful in high-strength precast, prestressed and shotcrete applications.
Reduced bleed and segregation
The fine particle size and high surface area (15–30 m²/g) increase cohesion of fresh concrete — ideal for self-compacting and pumped mixes.
Lower embodied carbon
Micro silica is a captured industrial by-product. Replacing part of the cement with microsilica reduces the CO₂ footprint of the mix.
Recommended micro silica dosage
Micro silica is dosed as a percentage of total cementitious material. Use a compatible superplasticiser (PCE) to maintain workability at low water-to-binder ratios (0.30–0.40).
| Application | Typical dosage |
|---|---|
| Standard structural concrete | 5 – 8% of cementitious content |
| High-strength / high-performance concrete | 8 – 10% |
| Shotcrete & repair mortars | 8 – 12% |
| Marine & aggressive-exposure concrete | 7 – 10% |
| Self-compacting concrete (SCC) | 5 – 8% |
Values are indicative. Always verify with trial mixes and project specifications.
Applications for micro silica concrete
Frequently asked questions
What is micro silica concrete?+
Micro silica concrete is concrete where a portion (typically 5–10%) of the cement is replaced with microsilica — an ultra-fine amorphous SiO₂ powder. This produces stronger, denser and more durable concrete than plain OPC mixes.
How much micro silica should I add to concrete?+
For most structural mixes, 5–10% of the total cementitious content by mass. Higher dosages (up to 12%) are used in shotcrete and severe-exposure environments. Always trial-mix and pair with a compatible superplasticiser.
Does micro silica make concrete waterproof?+
It does not make concrete literally waterproof, but it dramatically reduces permeability. Chloride penetration and water absorption typically drop by 50–70%, which is why it is standard in marine and infrastructure specifications.
Which standards apply to micro silica for concrete?+
ASTM C1240 (Standard Specification for Micro Silica Used in Cementitious Mixtures) and EN 13263 (Micro silica for concrete). Sio92 Microsilica complies with both.
Is micro silica the same as fly ash?+
No. Both are pozzolans, but micro silica is roughly 100× finer than fly ash and 100× more reactive. Fly ash is often used for workability and long-term strength; micro silica is used for early strength, low permeability and severe-exposure durability.
Need micro silica for your project?
Sio92 Microsilica complies with ASTM C1240 and EN 13263 and is available in bags, jumbo bags and bulk tankers with test certificates.
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