Towards Comparing Critical Degree of Moisture Saturation (SCrit) in Historic Brick Samples for Different Freezing Rates and Minimum Temperatures

As more historical buildings are being retrofitted, it is becoming more important to have an efficient procedure to test historic masonry’s capacity to withstand freeze-thaw cycling. Frost dilatometry testing focuses on establishing a critical degree of saturation (S_crit) at which masonry will fail if subjected to freeze-thaw cycles. Past studies in frost dilatometry attempt to reduce the total laboratory testing time by modifying different parameters, such as the freezing rate. This MRP focuses on the relationship between S_crit and freezing temperature, and S_crit and freezing rate. Brick samples from three historic masonry sites in Toronto were saturated at varying moisture contents between 60% and 100%. Three freezing temperatures, -2C, -6C and -15C, and three freezing rates, -5C/hr, -12C/hr and -21o C/hr, were tested. The samples were initially subjected to 12 cycles; however, upon discovering that there was little correlation in the data, an additional 30-cycle frost dilatometry tests were performed. As a result of this study, it was found that there is repeatable correlation between Scrit and freezing rate, with lower freezing rates resulting in higher S_crit values. While freezing temperatures also affect S_crit values, a definitive correlation between S_crit and freezing temperature was not established as part of this work. However, it was noted that the lowest freezing temperature (-15C) produced data that was more precise, and therefore it was generally easier to establish a linear trend to determine the S_crit values at the lowest freezing temperature.