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

摘要

This paper describes a series of experiments that were performed to assess the freeze-thawbehavior of mortar specimens exposed to NaCl solutions. A low-temperature longitudinalguarded comparative calorimeter was used to perform cyclic freeze-thaw testing on mortarspecimens saturated with NaCl solutions. Heat flow and acoustic emission activity weremonitored during the freeze-thaw experiment to detect ice formation and cracking. Although theconventional water-NaCl phase diagram would suggest that no freezing or damage would occurin specimens saturated with 15 % and 23.3 % NaCl solution by mass within the applied freezethawtemperature range, damage was observed. For these specimens, an additional heat flowpeak attributed to an unexpected phase change, accompanied by acoustic activity, was detectedat a temperature higher than the expected freezing point. To better understand the source of thisdamage, a low temperature differential scanning calorimeter was used to investigate theinfluence of NaCl on freeze-thaw behavior of water, two pore solutions, hydrated cementpowder, and calcium hydroxide powder. The results showed that the pore solution alters thefreeze-thaw behavior slightly; however, it does not exhibit the unexpected phase change athigher concentrations. The specimens made with hydrated cement powder showed theunexpected phase change in high concentrations of NaCl solution in a temperature rangebetween 0 °C and 8 °C. While the exact nature of this phase change is not definitively known, itappears that it results in premature damage during freeze-thaw when high concentration saltsolutions are used, even if freezing of the solution is not occurring.