Influence of negative temperature hardening on hydration, pore structure evolution and strength development of cement paste

Abstract

The pre-cured 24-h demolded cement pastes were directly cured at −5 °C and +20 °C for different ages to investigate the influence of negative temperature hardening on hydration, pore structure evolution, and strength development. Thermogravimetric (TG) results show that the inhibition effect of negative temperature hardening on the hydration degree and C–S–H gel content is different. As the hydration age increases to 120 days, the hydration degree and gel-space ratio of negative temperature hardening cement paste can reach the positive temperature hardening level of 120 days, while the C–S–H gel content is still lower than the positive temperature hardening level of 120 days. Mercury intrusion porosimetry (MIP) results indicated that negative temperature hardening increases all types of pore volumes, especially the pore volume of <10 nm. Similar to the hydration degree, by giving sufficient negative temperature hardening time (120 days), the pore characteristic parameters of negative temperature hardening cement pastes can approach the level of 120-day positive temperature hardening. Also, the fractal analysis shows that negative temperature hardening increases the proportion of large-diameter pores in the range of <100 nm, and decreases the proportion of large-diameter pores in the range of >3000 nm. In addition, the micro-mechanisms of limiting strength development are different at different negative temperature hardening stages. The early strength development is affected by the coupled effects of hydration and pore structure, while the later strength development is limited due to the lower C–S–H gel content.