Effect of the early-age frost damage and nano-SiO2 modification on the properties of Portland cement paste

Abstract

The effect of early-age frost damage on the hydration characteristics, pore structure and compressive strength of cement paste and the repair effect of nano-SiO2 on the damaged microstructure were investigated. The samples were prepared with nano-SiO2 content of 0% and 0.9% by weight of cement. The mercury intrusion porosimetry (MIP) data indicated that early-age frost damage can result in a part of small pores (20–100 nm) to become larger pores (100–300 nm) and nano-SiO2 particles can reduce the pores between 100 and 300 nm by the additional produced C-S-H gels and physical particle filling. The thermogravimetric (TG) results displayed the reductions in the hydration degree and the amount of C-S-H gels, while the pozzolanic nano-SiO2 particles reduced these losses to some extent. The differential scanning calorimetry (DSC) thermograms showed that early-age frost damage affected the structure of C-S-H gels formed and the attenuated-total-reflection (ATR) spectrums also indicated that it affected the polymerization of C-S-H gel silicate chains. Moreover, during the early-age freezing, the cement hydration reaction did not stop immediately but proceeded slowly until the non-freezable water was consumed out. The incorporation of nano-SiO2 can slightly enhance the compressive strength and hydration degree of cement pastes during the early-age freezing.