*2.1. Sample Preparation*

The absolute mass ratio of water, ordinary 42.5R Portland cement, and sand for pouring mortar was 0.5:1:1.8. The mechanical properties of the samples after 28 days of curing in water are shown in Table 1. Cubic samples of 100 mm in length, 100 mm in width, and 50 mm in height were prepared, from which some cylindrical samples of 25 mm in diameter and 30 mm in thickness were cut out (Figure 2). Mortar, like natural rocks, is a brittle material, and is often used in rock-breaking experiments, so the rock-breaking mechanism obtained from mortar is also applicable to natural rocks [13,23]. Since the mechanical properties of mortar samples from the same batch are almost identical, whereas the properties of natural rocks vary greatly, we used mortar to quantitatively study the effect of conductivity on rock damage.


**Figure 2.** Two types of concrete sample.
