Controllable in situ growth of highly dispersed nano-SiO2 on steel slag powder for enhancing cement-based materials.

To overcome the agglomeration of nano-SiO2 (NS) in cement-based materials, NS was grown in situ on the surface of steel slag powder (SSP) via a modified Stöber method, forming a composite particle (NS@SSP) with SSP as the core and in situ grown NS (INS) as the shell. The particle size and dispersion of INS were controlled by the water-to-ethanol ratio, TEOS concentration, and reaction temperature, while the nucleation mechanism and INS loading were governed by the SSP dosage. Under the optimal synthesis conditions (a water-to-ethanol ratio of 3 : 2, a TEOS concentration of 2 : 100, a reaction temperature of 40 °C, and a SSP dosage of ≥4 : 100 g mL-1), uniformly dispersed spherical INS of ∼50 nm was achieved, yielding an INS loading of ≤10.37 wt% and no free NS agglomerates. Critically, INS was covalently anchored to the surface of SSP via Si-O-Si bonds, ensuring the stability of the core-shell structure. Consequently, compared to ultrasonically dispersed NS, INS increased the cumulative hydration heat by 10.21% within 72 h, reduced the total porosity by 13.46% at 3 days, and enhanced the 3d compressive strength by 15.2% (from 45.3 to 52.2 MPa). This work demonstrates that the in situ growth strategy is a highly effective approach for harnessing the full seeding, filling, and strengthening potential of NS in cement-based materials.