Mechanism of nano-SiO2 internal generation for modification of cement-based materials

Abstract

In order to address the issue of agglomeration of nano-SiO2 mineral powder and maximize its nano-effect, a novel method is proposed to internally generate nano-SiO2 for modifying cement-based materials. Firstly, a highly stable nano-SiO2 precursor solution (NP) is synthesized by liquid-phase method. The existence state and precipitation evolution of SiO2 in NP are then studied based on the theory of silicic acid polymerization and rheological reaction kinetics. Then, the effects of NP on cement-based materials from microstructure (morphology, composition, pore) to macroscopic mechanical behavior are studied by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and mercury porosimeter. The results show that SiO2 in NP primarily exists in the form of silicate molecules, silicate oligomers, and colloidal particles, thereby avoiding the agglomeration problem commonly associated with solid nanoparticles. When NP is mixed with cement, the original NP dispersion system is destabilized, resulting in the precipitation of SiO2 as nanoparticles and fully utilizing the nano-effect. Consequently, the cement paste exhibits a denser microstructure and significantly higher compressive strength after hardening.