Acoustic Emission and Low-Temperature Calorimetry Study of Freeze and Thaw Behavior in Cementitious Materials Exposed to Sodium Chloride Salt

This paper describes a series of experiments that were performed to assess the freeze-thaw behavior of mortar specimens exposed to sodium chloride (NaCl) solutions. A low-temperature longitudinal guarded comparative calorimeter was used to perform cyclic freeze-thaw testing on mortar specimens saturated with NaCl solutions. Heat flow and acoustic emission activity were monitored during the freeze-thaw experiment to detect ice formation and cracking. Although the conventional water-NaCl phase diagram would suggest that no freezing or damage would occur in specimens saturated with 15% and 23.3% NaCl solution by mass within the applied freeze-thaw temperature range, damage was observed. For these specimens, an additional heat flow peak attributed to an unexpected phase change, accompanied by acoustic activity, was detected at a temperature higher than the expected freezing point. For better understanding of the source of this damage, a low-temperature differential scanning calorimeter was used to investigate the influence of NaCl on freeze-thaw behavior of water, two pore solutions, hydrated cement powder, and calcium hydroxide powder. The results showed that the pore solution alters the freeze-thaw behavior slightly; however, it does not exhibit the unexpected phase change at higher concentrations. The specimens made with hydrated cement powder showed the unexpected phase change in high concentrations of NaCl solution in a temperature range between 0 degrees C and 8 degrees C. Although the exact nature of this phase change is not definitively known, it appears to result in premature damage during freeze-thaw when high-concentration salt solutions are used, even if freezing of the solution is not occurring.