Issue 50

L. He et alii, Frattura ed Integrità Strutturale, 50 (2019) 649-657; DOI: 10.3221/IGF-ESIS.50.55 650 power level, the distance to rock, and the radiation time, were also shown to affect the intensity and distribution of temperature [12,15]. In addition to experiments, many researchers used numerical simulations to understand the failure processes in a rock exposed to microwave radiation. Whittles et al. [16] studied the influence of electric field strength on a two-phase rock under microwave radiation, and found that both the highest temperature and the highest temperature gradient occurred during the microwave-absorbing phase. Subsequently, other researchers [17,18] also showed that cracks originate around mineral crystals. Further, they found that microwave power, radiation time, and the ratio of the absorption phase to the transparent phase also affect the rock destruction results. In addition, the anisotropy, the dimensions and shapes of minerals affect the cracking of rock under microwave radiation [19-22]. Although significant research was done on this topic, there are only a few studies that address the effect of mineral distribution on rock structural failure under microwave radiation, such as schistosity. The schistosity structure of rock has been demonstrated to significantly affect the fracture patterns under mechanical loadings [23,24]. In addition, the failure of rock under microwave radiation (such as cracking and melting) was generally considered to reflect cumulative thermal damage, and failure was considered to occur gradually with increasing temperature [25-27]. Therefore, for a better understanding of the effect of microwave treatment on rocks, a study that addresses the effect of mineral distribution on the failure processes at high temperatures is necessary. This paper study focuses on investigating the response of schistosity structural rock to increasing temperature induced by microwave radiation. After microwave radiation, the microstructure, mineral composition, crystallisation changes, and mechanical performance were analysed to explain the failure mechanism in the schistosity structural rock under microwave radiation. M ATERIALS AND METHODS Materials he granite was obtained from the Qingyuan region of Liaoning province of China and it showed a clear schistosity structure. As shown in Fig. 1a, the rock block could be divided into dark and pale layers. The petrographic microscopic image of granite was prepared for observation using a polarising microscope (LABORLUX12 pol, Leitz). The petrographic thin section (Fig. 1b) shows that the Qingyuan granite has a medium-fine grain structure and is mainly composed of 65% feldspar, 22% quartz, and 11.5% biotite. In addition, most minerals exist in different degrees of alteration, such as feldspar as sericite. X-ray fluorescence (XRF, PANalytical B.V. Axios) was used to further determine the chemical compositions of the dark and pale areas, respectively, and the results are listed in Tab. 1. Tab. 1 shows that femic minerals (such as biotite) are mainly distributed in the dark area, while the light area is mainly composed of feldspar and quartz. Figure 1 : Appearance picture (a) and petrographic microscopy image (b) of virgin granite. (Pl-plagioclase; Mc-microcline; Qtz-quartz; Bt-biotite; Mag- magnetite). Oxide Content / wt. % SiO 2 Al 2 O 3 Na 2 O K 2 O Fe 2 O 3 CaO MgO Dark area 65.61 16.89 2.33 3.12 5.70 3.41 1.42 Pale area 78.61 10.79 1.68 6.00 0.22 1.74 0.07 Table 1 : Chemical composition of rock. T