Abstract: The variations of the diameter and mass attenuation of rock samples with the number of freezing-thawing cycles are obtained, and it is pointed out that 80 freezing-thawing cycles are the inflection points of the variation lines of diameter and mass of quartz sandstone. A technical method for the accurate CT identification of progressive damage is proposed, and the main damage areas of the sample are defined and subdivided. Moreover, the freezing-thawing damage model of progressive damage at stages before and after spalling is also established. Linear relationships between CT value, elastic modulus and porosity are established, and it is concluded that: (1) After 40 freezing-thawing cycles, the elastic modulus of the outermost ring layer is 0, and the CT value is not 0 at this time. Additionally, the ring layer doesn’t peel off. (2) After 80 freezing-thawing cycles, the CT value of the outermost layer is 0. Meanwhile, the porosity of the layer is the largest and the layer is peeling off. (3) The deterioration of the inner layer of the sample at the second stage is significantly greater than that at the first stage. According to this finding, the bundle hoop effect of the outer layer and the accelerated degradation effect of the inner layer are proposed, which can also be explained based on the mechanical mechanism. On the basis of images of changes in porosity, loss rate of elastic modulus and mesopore after several freezing-thawing cycles, the development and evolution of progressive damage are further quantitatively illustrated. Based on the variation law of elastic modulus and porosity with the number of freezing-thawing cycles, respectively, the degradation factor “ ” of the freezing-thawing elastic modulus is defined, and a formula for predicting the elastic modulus degradation of progressive damage is also established based on the zone division of progressive damage. Finally, the feasibility of the above method is verified by comparing the calculated values with the measured values.

Key words: precise CT identification technology, progressive freezing-thawing damage, bundle hoop effect, mesopore variation, degradation factor of elastic modulus