Silica fume is a critical component in producing high-performance concrete for modern urban construction. It fills voids between cement particles and reacts with hydration products to form gel, significantly enhancing concrete's overall performance.

Pore Structure Refinement and Interfacial Transition Zone Strengthening:

· Physical Filling: The average particle size of silica fume is about 1/100th that of cement particles, enabling it to effectively fill the micron-sized pores between cement particles, resulting in a denser concrete matrix.

· Chemical Effect: The highly reactive amorphous SiO₂ in silica fume undergoes a secondary pozzolanic reaction with Ca(OH)₂, a product of cement hydration, generating additional C-S-H gel (calcium silicate hydrate). This not only consumes the weak Ca(OH)₂ crystals but also significantly strengthens the Interfacial Transition Zone (ITZ) between the cement paste and aggregates, which is the weakest link in conventional concrete and the key to silica fume's strength enhancement.

Quantitative Improvement in Mechanical and Durability Properties:

· Strength: With an optimized mix design, silica fume can increase the 28-day compressive strength of concrete from the conventional 40-60 MPa to over 100 MPa, even reaching 150 MPa.

Durability:

· Chloride Ion Penetration Resistance: According to ASTM C1202 (coulomb charge test), the charge passed for silica fume concrete can drop from over 4000 coulombs for conventional concrete to below 1000 coulombs, rated as "very low" permeability, significantly extending the service life of marine structures and bridges.

· Sulfate Attack Resistance: By reducing the Ca(OH)₂ content in the cement paste, it diminishes the risk of reactions with sulfates that form expansive products (e.g., ettringite).

Recommended Dosages for Application Scenarios (Reference):