A Method for Determining the Fracture Toughness of Shotcrete Materials Subjected to Freeze-Thaw Cycles.

Defects can be introduced into shotcrete materials after a few freeze-thaw cycles, which has a significant influence on the fracture performance of shotcrete. In this study, a series of shotcrete specimens with varying sizes, geometries, and initial crack lengths were prepared to investigate the fracture properties of notched shotcrete under freeze-thaw conditions. Considering the effects of specimen boundaries and material microstructure, a linear closed-form solution was proposed to determine the fracture toughness of frost-damaged shotcrete. The fracture toughness was found to be a reliable material constant, independent of specimen geometry variations. Results from three-point bending (3PB) tests show that freeze-thaw cycles severely weaken the fracture toughness of shotcrete, which is consistent with CT scan images of the damaged microstructure of the shotcrete specimens. Moreover, specimens with longer initial notches exhibited more severe freeze-thaw damage, which should be carefully considered in practical engineering assessments. These findings highlight the critical importance of considering freeze-thaw effects and notch length when evaluating the durability of shotcrete in cold region applications.