Keywords
pore solution, sodium chloride, differential scanning calorimeter, porosity, concrete
Presentation Type
Event
Research Abstract
A low-temperature longitudinal guarded comparative calorimeter was used to perform cyclic freeze-thaw testing on mortar samples saturated with NaCl solutions. Heat flow activity was monitored during the freeze-thaw experiment to detect ice formation and cracking. While the conventional water-NaCl phase diagram would suggest that no freezing or damage would occur in samples saturated with 15 % and 23.3 % NaCl solution by mass within the applied freeze-thaw temperature range, damage was observed. For these samples, an additional heat flow peak accompanied by acoustic activity was detected at a temperature greater than the expected freezing point. To better understand 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 additional phase change at higher concentrations. The samples made with hydrated cement powder showed the unexpected phase change in high concentrations of NaCl solution in a temperature range between 0 °C and 8 °C. While the exact nature of this phase change is currently not definitively known, it appears that it results in a premature damage development during freeze-thaw when high concentration salt solutions are used, even if freezing of the solution is not occurring.
Recommended Citation
Allison Hampton and Jason Weiss,
"Low Temperature Calorimetry Study of Freeze and Thaw Behavior in Cementitious Materials Exposed to NaCl Salt"
().
The Summer Undergraduate Research Fellowship (SURF) Symposium.
Paper 38.
https://docs.lib.purdue.edu/surf/2013/presentations/38
Low Temperature Calorimetry Study of Freeze and Thaw Behavior in Cementitious Materials Exposed to NaCl Salt
A low-temperature longitudinal guarded comparative calorimeter was used to perform cyclic freeze-thaw testing on mortar samples saturated with NaCl solutions. Heat flow activity was monitored during the freeze-thaw experiment to detect ice formation and cracking. While the conventional water-NaCl phase diagram would suggest that no freezing or damage would occur in samples saturated with 15 % and 23.3 % NaCl solution by mass within the applied freeze-thaw temperature range, damage was observed. For these samples, an additional heat flow peak accompanied by acoustic activity was detected at a temperature greater than the expected freezing point. To better understand 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 additional phase change at higher concentrations. The samples made with hydrated cement powder showed the unexpected phase change in high concentrations of NaCl solution in a temperature range between 0 °C and 8 °C. While the exact nature of this phase change is currently not definitively known, it appears that it results in a premature damage development during freeze-thaw when high concentration salt solutions are used, even if freezing of the solution is not occurring.
Comments
From a paper co-authored by Yaghoob Farnam, Allison Hampton, Dale Bentz, and Jason Weiss.