Comparative study on effects of pozzolanic nano-SiO2 and non-pozzolanic nano-TiO2 on the microstructure and macro properties of cement paste subjected to early-age frost attack

Abstract

The effects of nano-SiO2 (NS) and nano-TiO2 (NT) on the microstructure, strength and chloride diffusivity were compared, and the mechanism of both nanoparticles on early-age frozen cement paste was revealed. The thermogravimetric (TG) results demonstrate that NS effectively increases C-S-H gel content and degree of hydration to make up for hydration loss due to early-age frost attack, while NT had little effect on compensating for hydration loss. The mercury intrusion porosimetry (MIP) results indicate that NS and NT have the same improvement mechanism for frost-damaged pore structures, while NS has a better improvement effect on pore structure than NT. The macro results show that the enhancement effects of NS and NT on strength are similar, while the improvement effect of NS on chloride diffusivity is much better than that of NT. Finally, it is concluded that, in the early-age frozen cement paste, NS promotes cement hydration and optimize pore structure through pozzolanic effect, while NT mainly improves pore structure through nano-filling effect.