Failure Characteristics of Rock-like Mortar Specimens with Arc-shaped Flaws under Freezing-thaw Cycles and Uniaxial Compression

To investigate the freeze-thaw (F-T) damages and failure characteristics of rock mass with arc-shaped joints in cold regions, three types of cement mortar specimens with different central angles and prefabricated arc-shaped flaws are subjected to uniaxial compressive tests under different F-T cycles. Experimental observations show that the uniaxial compressive strength of specimens are significantly influenced by F-T cycles and their failure modes are mainly affected by the central angle a of the prefabricated flaws. Unlike the specimens with a central angle of 60 degrees, the specimens with a central angle of 120 degrees and 180 degrees have greater curvature of flaws, so tensile cracks occur in the arc-top area of their prefabricated flaws. According to experimental images observed by environmental scanning electron microscope (ESEM), as the number of F-T cycles increases, the deterioration effect of the specimen becomes more obvious, which is specifically reflected in the increase of the mass loss, peak stress loss, and damage variables as a power function, and the peak strain decreases as a quadratic polynomial. According to numerical results using two-dimensional particle flow code (PFC2D), it is found that F-T cycles cause more damage to the specimen in the early stages than in the later ones. The area of the concentrated compressive stress zone in the middle is decreased due to the increased number of F-T cycles, while the area of the surrounding tensile-shear stress zone is increased. The models appear different failure modes due to the release of concentrated stress in different tensile-shear zones.