Deicing salts are often applied to the surface of pavements and bridge decks in the winter to melt ice; thereby improving safety for the travelling public. In this paper, the influence of NaCl deicing salt on freezing and thawing temperatures of pore solution was evaluated and corresponding damage during freezing and thawing of mortar specimens was investigated. A low-temperature longitudinal guarded comparative calorimeter (LGCC) was developed to cool down a mortar sample at a rate of 2 °C/h and to re-heat the mortar at a rate of 4 °C/h. Heat flux during freezing and thawing cycles was monitored, and the temperatures at which freezing and thawing events occurred were detected. During cooling and heating, acoustic emission activity was measured to quantify the damage (cracking) due to aggregate/paste thermal mismatch or phase changes. The results show that NaCl solution in a mortar sample freezes at a lower temperature than the value expected from its bulk phase diagram, while the frozen solution in mortar melts at the same melting temperature as the bulk frozen NaCl solution. As the salt concentration increases, the freezing temperature is reduced. For samples containing more highly concentrated solutions, another exothermic event is observed whose corresponding temperature is greater than the aqueous NaCl liquidus line in the phase diagram. For mortar samples saturated by solutions with 5 % and 15 % NaCl by mass, greater freeze/thaw damage is observed. The AE calorimeter developed herein is applicable for investigating damage behavior during freezing and thawing of different phases in pore solution (in mortars).
Citation: Advances in Civil Engineering Materials
Pub Type: Journals
Acoustic emission, calorimeter, deicing salts, freeze and thaw, heat flow, NaCl