Investigating the effects of microwave treatment on the strength of igneous rocks

Rock drilling and cutting technology has developed rapidly in the last century. However, there are problems in drilling and cutting very hard rocks such as low penetration rate and high wear rate of cutting tools. In order to increase the advance rate and reduce wear during drilling or cutting of very hard rocks, recent studies on some innovative methods such as microwave assisted rock breakage has been drawing attention. Studies on the effects of microwave exposure on the mechanical properties of igneous rocks are new and limited. Therefore, there are many gaps to be investigated in this area. In this thesis, the effects of microwave treatment were investigated on the strength of igneous rocks. In this study, microwave energy up to 6 kW was applied to 9 different magmatic rocks such as; 6 granite, 2 syenite and 1 gabbro. First, thin sections of each rock used in the experiments were prepared and the mineral contents and percentages were determined. Then, the uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS), density, porosity, and ultrasonic wave velocity tests were carried out. After that, more than 600 samples were exposed to microwave energy. The microwave treatment was applied at 1 kW, 2 kW, and 6 kW powers for the durations ranging from 60 s to 420 s. The surface temperature of each specimen was measured with an infrared gun before the microwave irradiation and immediately after removing the sample from the oven. The evaluation of the results show that the rock strength decreases generally with increasing microwave power and exposure duration. The strength losses and the heating degrees are different for each tested rock type illuminated by microwave power because of the different the mineral content. crackings and meltings were observed on some samples depending on the applied microwave power, the exposure duration, and the mineral content. The UCS and the BTS values of granites decreased usually after 200 ℃ and 100 ℃, respectively. The significant losses in the strength of syenite and gabbro samples were generally observed below 100 ℃ due to their metallic mineral contents or high amount of microwave absorber minerals. Concluding remark is that microwave treatment affects strongly the strength of igneous rocks depending on the applied power, the exposure time, and mineralogy.