Measuring Freeze and Thaw Damage in Mortars Containing Deicing Salt Using a Low-Temperature Longitudinal Guarded Comparative Calorimeter and Acoustic Emission

Abstract

Deicing salts are often applied to the surface of pavements and bridge decks in the winter to melt ice, thereby improving safety for the traveling public. In this paper, the influence of NaCl deicing salt on freezing and thawing temperatures of pore solution and corresponding damage of mortar specimens were 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 (AE) activity was measured to quantify the damage (cracking) caused by aggregate/paste thermal mismatch and/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 because of under-cooling. Conversely, 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 lowered. For samples containing more highly concentrated solutions, an additional exothermic event is observed whose corresponding temperature is greater than the aqueous NaCl liquidus line in the phase diagram. Damage also begins to occur at this temperature. 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).

An Overview of Joint Deterioration in Concrete Pavement: Mechanisms, Solution Properties, and Sealers

“…The acoustic emission was used to relate this phase change with damage. For more description see (16).…”

“…This can develop a zone with a high degree of saturation. This high level of saturation can result in freezing damage and/or in chemical reaction in some systems (e.g., the formation of Friedel salt that can infill air voids (5,(7)(8)(9)(10)(11), the production of oxychloride (15,16), or the replacement of calcium in calcium silicate hydrate (3)). While this mechanism would explain the 'soft zone' frequently observed at the base of the saw-cut, an alternative damage pattern is observed with the side of the saw-cut flaking off in layers that are fractions of an inch thick.…”

“…There are several publications that contain additional details on the experiments performed; however, many of these details are not included in this document to assist users by providing a document that is shorter and less burdened by testing details. This report has five distinct sections: First, it will discuss the working hypothesis the authors have used to discuss some of the important aspects of freezing damage in concrete with and without deicing salts (12,16,30). Second, the work discusses how salts will alter the physical properties of the solution and how this influences drying and wetting (31,32).…”

“…In the concrete literature, the majority of the interest in deicing salts research is related to durability (55), on hysteresis during drying and wetting (12,56), on freezethaw and salt solutions damage (16,57,58) or crystallization pressure (17). Spragg et al (31) examined changes in density, activity, surface tension and viscosity as a function of the concentration of salt solutions; however, a limited number of measurements have been reported in literature.…”

Saturation of Air Entrained Voids and Its Implication on the Transport of Ionic Species in Concrete

“…The air voids are usually larger than the capillary pores [10 nm to 10 mm (Mindess, Young, & Darwin, 2003)] of the cementitious systems, and ideally are isolated from each other but connected with the capillary pore systems of the cementitious matrix (Litvan, 1988;Sutter, Van Dam, & Thomas, 2007). Entrained air voids that remain unsaturated in service can release pressure for the expansive ice formation under the freezing temperature (Fagerlund, 1977;Farnam, Bentz, Sakulich, Flynn, & Weiss, 2014;Li, Pour-Ghaz, Castro, & Weiss, 2012;Pinto & Hover, 2001). …”