Determination of Dynamic Tensile Strength of Microwave-Induced Basalt Using Brazilian Test.

Research on the dynamic tensile behaviour of microwave-irradiated rock is of great significance to microwave-assisted tunneling and mining. In order to study the effect of microwave heating and rapid cooling on the mechanical properties of basalt, dynamic Brazilian splitting tests were conducted using the split Hopkinson pressure bar (SHPB) equipment. Brazilian specimens were treated at microwave radiation (with different microwave powers and exposure times) and water cooling (after microwave processing) before the dynamic split test. The influence of microwave irradiation power (1–4 kW) and exposure time (10–40 s) on the surface temperature, P-wave velocity, and dynamic tensile strength of the basalt specimens have been studied. Test results indicate that the treatment has negative effect on the rock P-wave velocity and dynamic tensile strength, and high power and low time radiation can cause more damage than the specimens treated at low power and long time radiation, though equivalent microwave energy is exerted on the basalt samples. For example, the average rock dynamic tensile strength for the specimen treated at 1 kW for 40 s, 2 kW for 20 s, and 4 kW for 10 s is 37.51 Mpa, 37.98 MPa, and 31.94 MPa, respectively, which decreases by 13%, 12%, and 26% compared with the untreated specimens. When the specimens were heated at 4 kW for 28 s and longer, they break into debris abruptly and accordingly lost their bearing capacity. The internal structural characteristics of the treated basalts were studied using scanning electron microscopic (SEM) technique. These photographs showed that micro-cracks appear on the rock surface after microwave radiation and water cooling treatment. It confirms the damage caused by microwaves to basalt specimens on the microscopic level and provides an internal reason for the reduction in dynamic tensile strength and P-wave velocity. The research can provide certain experimental support for microwave-assisted mechanical rock breaking. [ABSTRACT FROM AUTHOR]