Silica fume

Silica fume (CAS 69012-64-2) is an ultrafine industrial byproduct collected during silicon and ferrosilicon alloy production.

Where is Silica fume used?

• Cementitious systems: pozzolanic binder and rheology modifier
• High-performance concrete: reduces permeability and increases compressive strength
• Bridges, marine structures and tunnel linings
• Refractory furnace linings and ladles: improves castable flow and sintered density
• Mining shotcrete: accelerates early strength gain and reduces rebound loss in underground support
• Pulp and paper facilities use the product in cementitious flooring and containment structures.
• Used in concrete, UHPC, refractory materials, oil well cement and industrial composites.
• In gypsum board, improves fire resistance and core strength.

Good to know: Densified grades are often preferred for bulk handling and reduced dusting. Standard grades conform to ASTM C1240 and EN 13263 specifications, which define minimum SiO₂ content and physical requirements for use in concrete.

Formulation notes

• Typically replaces 5–12% of cementitious material, while fly ash (Class F) replaces 15–30% and slag (GGBFS) replaces 25–50%.
• A dosage greater than 5% on cement, in the absence of superplasticizer, is not recommended because it increases water demand and causes a decrease in strength.

Typical specification

• Silica content can vary from about 85% to 98%.
• Specific surface area is 15-20 m2/g.
• Bulk density ranges from 0.2 kg/l for loose material to 0.5 kg/l for compacted material.
• Buyers should verify SiO2, loss on ignition, moisture content, particle size and densification degree together when purchasing.

Regulatory status

• ASTM C1240 requires a minimum of 85% amorphous SiO2.

Storage, packaging and handling

• Must be protected from moisture during storage.
• Packaging should be selected according to factory equipment and project schedule to ensure moisture protection during storage.

Frequently asked questions about Silica fume

What factors determine the actual performance of silica fume in a formulation?

Performance depends on aggregation degree, bulk density, moisture content, carbon content and compatibility with water reducers and dispersants, not only on silica content.

Technical content is compiled and updated by the SoleChem product team from public technical sources; the certificate of analysis (COA) governs product-specific specifications.