Research on the nano-micro interaction mechanism of nano-SiO2 particles in cement paste

Abstract

The poor dispersion and severe agglomeration of externally added nano-SiO₂ powder represent a persistent technical bottleneck restricting its performance enhancement efficiency in cement-based materials. This study develops an acidic nano-SiO₂ precursor solution using acetic acid as the stabilizing medium and industrial water glass as a low-cost silicon source. A combined investigation incorporating pH gradient stability tests, saturated Ca(OH)₂ simulated pore solution reactions, cement paste performance comparisons, transmission electron microscopy (TEM) / energy dispersive spectrometer (EDS) characterizations, and Materials Studio molecular dynamics simulations is conducted to systematically reveal the nanoparticle stabilization mechanism in the precursor, and its precipitation behavior and modification effect in cementitious environments. Results show that precursors with pH ≤ 6 exhibit excellent long-term storage stability, as acetic acid molecules adsorb onto SiO₂ surfaces through hydrogen bonding and electrostatic interactions to form a protective shell that inhibits agglomeration. The weakly acidic precursor (pH=6) achieves an optimal balance between stability and reactivity: when exposed to the alkaline cement matrix, acetic acid is neutralized, inducing in-situ precipitation of monodisperse SiO₂ nanoparticles that uniformly distribute within the pore structure and on cement particle surfaces. These in-situ generated nanoparticles exert nucleation seeding and micro-filling effects, promoting calcium silicate hydrate gel formation and refining pore structure, fundamentally eliminating the agglomeration issue associated with conventionally added nano-SiO₂ powder. This work provides a cost-effective technical pathway and theoretical basis for the efficient application of nano-SiO₂ in cement-based construction materials.