The sandstone terrain is widely distributed in South Korea, especially in the Gyeongsang basin. Herein, it may be important to note that the Gyeongsang supergroup consists of three lithostratigraphic units including Sindong, Hayang, and Yucheon groups [13–14]. Adequate samples, in the scientific sense, can be found in the Hayang group due to their quartz composition. We first recovered 20 samples and labelled them into four categories from S1 to S4 concering to their average proportion (Fig. 1). Results revealed that the sandstone is mostly consisted of quartz with a subordinate amount of feldspars. A QFL ternary plot is based on Q (monocrystalline quartz + polycrystalline quartz), F (plagioclase + feldspar), and L (aphanitic lithic fragment) contents. All samples were found to have very few lithic contents.
The samples were cut into ∅50 × 30 mm disc specimens before the heating process. Thermodynamic studies of various stones suggest that it is imperative to have a slow rate of heating, since the microstructure may undergo morphological, physical, and mineralogical changes [15–16]. To sufficiently observe the sample characteristics, the samples were heated at a rate of 5°C min− 1 from 50 to 500°C. An experimental contour modelling was conducted by their porosity and the void ratio [17–19]. As reported previously, porosity is a fundamental property which reflects the transport behavior of rock strength. When the rock has low porosity, it could bear a higher load than vice versa. The saturated mass (Msat) and the dried mass (Ms) of the sample were measured and the porosity (n) was calculated using the following Eq. 1;
\(n=\left(\frac{{M}_{sat}- {M}_{s}}{{p}_{w} \times V}\right)\times 100\) Eq. 1
where pw is density and V is a bulk volume of water. The mercury intrusion porosimetry method is based on the Washburn equation and adopted to observe the void ratio [20]. Values of the void ratio can be expressed as Eq. 2;
\(e= \frac{Vs}{Vm}\) Eq. 2
where Vs is the volume of the sample and Vm is the cumulative volume of mercury. The mass loss was observed using TGA, while the specific gravity was obtained from an automated gas pycnometer. Here, samples were ground to powder using a grinder before the experiment.