Evaluation and classification of non-linear loss on uniaxial compressive strength of building stones exposed to weathering by freeze–thaw cycles

Cold climates accelerate the weathering of building stones via freeze–thaw (FT) cycles. This situation causes natural stones to begin to lose their integrity and subsequently decreases their strength. This study was conducted to demonstrate the impact of FT cycles on the course of uniaxial compressive strength (UCS) on very large number of natural stone sample types. For this purpose, 46 sample groups were subjected to 4, 7, 10, 14, 20, 28, 35, 56, 70, and 84 FT cycles under laboratory conditions, and UCS values were determined at the end of cycles. Additionally, ultrasonic P-wave velocities (V_P) were measured in three directions on each fresh cubic sample, and the anisotropy coefficient (C_A) was calculated. The effect of anisotropy to the strength loss of natural stones due to FT cycles was evaluated by the C_A coefficients. Results suggested that the non-linear UCS loss, notably up to 35%, especially for the stones having greater than 5% open porosity (n). In addition, it has been revealed that sample groups with calculated C_A coefficients above 15% are more prone to deterioration due to FT cycles. The Frost Resistance Index (FRI), defined as the ratio of the UCS value obtained after a specific FT cycle to the UCS value obtained on the fresh sample, was calculated for all groups at the end of respective cycles. A generalized classification system consisted of “very high”, “high”, “moderate”, “low” and “very low” classes based on the FRI parameter for deteriorated building stones has been proposed for practice.