Exploring the potential of nano-SiO2 to prevent early-age frost damage in Portland cement paste

The purpose of this study is to explore the potential of nano-SiO2 (NS) to prevent early frost damage, and the effect of nano-SiO2 (NS) on cement pastes subjected to early-age freezing was investigated regarding the macro properties (strength and durability) and micro properties (hydration and microstructure). The specimens were prepared with NS content of 0%, 0.6%, 0.9% and 1.2% by weight of cement. The results indicated that nano-SiO2 has a positive impact on the macro properties of cement pastes frozen at early ages, compared with reference specimen. The cement pastes containing 0.9% NS achieved the best enhancements of 22.6% and 30.9% in compressive strength and chloride ion penetration, respectively. The TG results indicated that the additional nano-SiO2 particles can increase the hydration degree of cement paste and the MIP data indicated that nano-SiO2 particles reduced the total porosity and other pore structure parameters. This is because the additional C-S-H gels produced by the pozzolanic effect of nano-SiO2, and nano-filling of nano-SiO2 particles refine the pore structure of cement matrix. Moreover, XRD results showed that nano-SiO2 also reduce the Ca(OH)2 orientation in cement matrix