Microcracking behavior transition in thermally treated granite under mode I loading

• Published in: Engineering geology 2021-03, Vol.282, p.105992, Article 105992
• Main Authors: Guo, Tian Yang, Wong, Louis Ngai Yuen, Wu, Zhijun
• Format: Article
• Language: English
• Subjects: Acoustic emission; Granite; Microcracking behavior; Semi-circular bending test; Thermal treatment
• ISSN: 0013-7952; 1872-6917
• DOI: 10.1016/j.enggeo.2021.105992

An in-depth understanding of the thermomechanical properties of rocks is fundamentally important in many fields of geotechnical engineering. However, the microcracking mechanisms of thermally treated granite under mode I loading are very complex. To investigate the effect of thermal treatment on the microcracking behavior, we perform mode I three-point bending tests on a set of pre-notched semi-circular specimens. The specimens are pre-heated to different target temperatures (i.e. 50 °C, 100 °C, 150 °C, 200 °C, 400 °C, and 600 °C), which are then naturally cooled down to room temperature. Acoustic emissions are monitored during the loading tests to provide clues on the microcracking processes. The fracture process zone (FPZ) development features before the initiation of macrofracture are interpreted through analysis of the spatial-temporal evolution of AE events. Based on the AE signatures, we identify the microcracking behavior transition phenomenon as the thermal treatment temperature increases from 150 °C to 200 °C, which is related to the development of thermal microfractures. As the transition occurs, we observe (1) relatively lower load levels at the beginning of the rapid FPZ development phase; (2) longer rapid FPZ development duration; (3) larger size and maximum event density for fully-developed FPZs. Taking the microscopic observation into consideration, we propose an extended conceptual model to describe the FPZ evolution before the unstable fracture propagation in crystalline rocks. The present findings provide useful insights into the microcracking behavior in geoengineering practices where the host rocks are subjected to temperature changes. •Pre-notched semi-circular thermally-treated granite specimens under mode I loading•Microcracking behavior of the specimens studied by interpreting acoustic emission.•Microcracking transition occurs as the temperature increases from 150 °C to 200 °C.•The transition marks the onset of increased microfracture amount and density.