Dispersion of in-situ controllably grown nano-SiO2 in alkaline environment for improving cement paste

Abstract

Nano-SiO2 (NS) has attracted considerable cementitious interest due to the new potential uses of nanoparticles. However, the dispersion problem of NS in alkaline cement environments has restricted its real application. Therefore, in situ-grown NS (INS) on the surface of iron tailings powder (ITP) can also be uniformly dispersed in the cement-based material by taking advantage of the inert ITP admixture's property of being easily and uniformly dispersed in the cement, simultaneously effectively controlling the particle size and the amount of growth of NS. To this end, the characteristics and dispersion stability of INS were evaluated by TEM, SEM, FTIR, XRD and other characterization methods, and the results showed that an amorphous nano-silica layer can be uniformly adsorbed on the surface of ITP, which was conducive to effectively decreasing the aggregation of NS. Compared with commercial NS, INS can better promote cement hydration and reduce the moisture wrapped by NS agglomerates, thus maintaining a good fresh property, and INS can also improve the early and long-term compressive strength of cement pastes. Moreover, the hydration reaction and microstructural evolution were evaluated and comparison with commercial NS through isothermal calorimetry, XRD, TG/DTG, NMR, MIP and BSEM analyses. This work has opened a new strategy to develop NS as a nano reinforcing material for cement composites.