Effect of freezing and thawing process on fracturing mechanism and acoustic emission characteristics of notched semi-circular bend specimens of red sandstone

Abstract

Understanding the effect of freeze-thaw (F-T) cycles on the fracture mechanism of rocks under mode-I loading is exceptionally prominent in addressing the underlying factors of rock engineering under a frosty environment. A three-point bending test was carried out on sandstone specimens exposed to 0, 10, 20,40, 60 and 80F-T cycles to achieve the fracture parameters. Moreover, the digital image correlation (DIC) and acoustic emission (AE) methods were employed to reveal the progressive failure in different loading stages. The results divulged that the F-T cycles significantly influenced the fracture parameters, including fracture toughness (KIC) and fracture energy (Gf). The average KIC values have given a negative linear relation with increasing F-T cycles. The percentage of KIC drop with F-T cycles is 9.78 %, 12.20%, 18.56%, 27.2%, and 31.60% for samples treated with 10, 20, 40, 60, and 80 cycles, respectively, while the fracture energy (Gf) gives a decline-rise trend from 0 to 10 and 20 to 80 cycles. The AE signals have demonstrated an apparent stage characteristics, and a sudden rise has occurred in the AE count rate at peak loading, revealing the fracture zone of rock under loading. The DIC effectively revealed the progressive failure pattern, especially at the later loading stages. When the load progressed to around 80–90% of maximum loading, a diverse high-strain region appeared at the tipping point, and the high-strain area continued to develop. The results of this study can effectively address the complex fracturing phenomenon of rocks and provide valuable insights into construction and engineering operations in cold climates.