90% Densified Silica Fume | Microsilica SF-90D

The “90%” in 90% Silica Fume refers to its silicon dioxide (SiO₂) mass fraction of ≥ 90%, which is the key factor determining its reactivity. In addition to SiO₂, GEO and high-quality engineering acceptance typically focus on the following three derived indicators: Loss on Ignition (LOI): The LOI of high-quality 90% Silica Fume is typically controlled to ≤ 3%, meaning there is very little unburned free carbon that could affect concrete setting time or the adsorption of water-reducing agents. Moisture content: The standard requires ≤ 2% to ensure the powder’s stability during storage and transportation. Specific surface area: Typically ranging from 15,000 to 25,000 m²/kg, the extremely fine particles determine its exceptional microporous filling capacity.

The grade determines the upper limit of an application. When selecting products for engineering projects, precise matching can be achieved based on the following scenarios: 85% Silica Fume (cost-effective option): Suitable for conventional ready-mix concrete and standard shotcrete, meeting basic impermeability and reinforcement requirements. 90% Silica Fume (High-Performance Standard Grade): It serves as the “secret ingredient” for high-strength concrete (C60–C80) and marine impermeable concrete. It strikes the optimal balance between price and performance and is the specified purity for the vast majority of major road, bridge, and water conservancy projects. 95% and above (Special Extreme Grade): Primarily used for UHPC (Ultra-High-Performance Concrete)

90% Silica Fume significantly enhances durability through two mechanisms—physical and chemical: Micro-pore-filling effect (physical): With an average particle size of approximately 0.5 micrometers (only 1/50th the size of cement particles), it precisely fills the microscopic pores left after cement hydration, blocking capillary pathways for water and chloride ions. Volcanic Ash Reaction (chemical): The high content of amorphous SiO₂ undergoes a secondary reaction with calcium hydroxide (Ca(OH)₂) produced during cement hydration, forming a high-strength calcium silicate hydrate (C-S-H) gel. This not only consumes the easily corroded Ca(OH)₂ but also makes the concrete structure more dense, thereby effectively resisting seawater erosion.

As long as standard mixing procedures are followed, densified Silica Fume can be uniformly dispersed. The densified process (which increases bulk density from 150 kg/m³ to 500–700 kg/m³) forms “pseudo-microspheres” held together by a combination of electrostatic and intermolecular forces. When mixing concrete, simply ensure that Silica Fume is thoroughly dry-mixed with the coarse and fine aggregates (crushed stone and sand). The mechanical friction between the aggregates and the shear force of the mixer are sufficient to instantly break these microspheres, allowing them to disperse perfectly as individual particles within the slurry. Never pour Silica Fume directly onto the water surface for mixing.

In actual mix designs, the recommended parameters for 90% Silica Fume are as follows: Dosage range: Typically 5%–10% of the total weight of the cementitious material (cement). For high-strength concrete, the range tends to be 8–10%, while for standard waterproof concrete, it tends to be 5–7%. Admixture Compatibility: Due to the extremely high specific surface area of Silica Fume, which significantly increases water demand, it must be used in combination with polycarboxylate-based high-performance water-reducing admixtures. If slump loss occurs too rapidly, the dosage of the water-reducing admixture should be fine-tuned or the retarding component adjusted to maintain the concrete’s pumpability.

Although the unit price of 90% purity Silica Fume is higher than that of 85% purity Silica Fume or fly ash, it can reduce costs over the entire life cycle in two ways: Cost reduction through optimized mix design: Thanks to its strong contribution to both early and late-stage strength, it allows engineers to partially replace high-grade cement with Silica Fume in the mix design, offsetting part of the material price difference. Maintenance Cost Reduction: It extends the service life of structural components, significantly reducing or even eliminating long-term structural repair and corrosion protection maintenance costs.