Influence of NaCl on the ice formation process in ordinary and air-entrained mortar based on LF-NMR

Understanding the ice formation process in cement-based materials is necessary to evaluate the freeze-thaw durability of concrete structures serviced in cold regions. However, the influencing mechanism of deicing salt on the ice formation process in cement-based material remains unclear. In this paper, the influence of NaCl on the ice formation process in the mortar was investigated by tracking the state and movement of pore water during the ice formation process using the low-field nuclear magnetic resonance (LF-NMR) technique. The obtained results show that during the ice formation process, the movement of pore water after being saturated with NaCl solution from the gel pore to the capillary pore is more distinct, regardless of ordinary and air-entrained mortar. Moreover, the increase of the signal amplitude of LF-NMR illustrates that NaCl solution promotes the conversion of chemically bound water to physically absorbed water. This effect leads to an increase in the free water content, and the saturation of the capillary pores is vulnerable to reaching critical saturation.