Rock is a complicated material which includes randomly distributed grains and cracks. The reliability of rocks under fatigue load is very important during the construction and operation of rock engineering. In this paper, we studied the deformation and failure process of red sandstone under fatigue load in a laboratory based on a new division method of strain energy types. The traditional elastic strain energy density is divided into two categories: grain strain energy density and crack strain energy density. We find that the proportion of the grain strain energy density to total strain energy density can be used as an indicator of rock yield and the proportion of the crack strain energy density to total strain energy density can be used as an indicator of rock failure. Subsequently, through extensive literature research, we found that such a phenomenon is widespread. We also find the proportion of grain strain energy density to total strain energy density when yielding is affected by rock types and elastic modulus. The proportion of crack strain energy density to total strain energy density in the pre-peak stage is stable and not affected by rock types and elastic modulus, which is about 0.04~0.13. These findings should be very helpful for rock stable state judging in rock engineering.

Inner stress exists in rocks, affecting rock engineering, yet has received very little attention and quantitative investigation because of uncertainty

Ginger nut, AGA soil, and shell lime are the primary building limes used in traditional Chinese architectural sites. They have been widely researched and developed for restoring rock and soil heritage over the last decade. Previous studies have shown that these materials are compatible with weathered rock in terms of mechanical properties and environmental adaptability. In this study, metakaolinite was added to Chinese hydraulic limes to improve the mortar abilities. The basic properties and weather abilities of the mortars were evaluated. The characteristics of carbonation and hydration were analyzed over 900 days. The results indicated that the early strength improved and the contracting rate reduced when metakaolinite was added. The shell lime mortar was improved considerably compared with the modified ginger nut and AGA soil. The lime mortar content was determined using the X-ray diffraction results. The carbonation and hydration characteristics revealed that the metakaolinite aided the generation of hydraulic products (Ca₂Al₂SiO₇·nH₂O and β-CaSiO₃·nH₂O), particularly in the early stage. The microstructures were observed by scanning electron microscopy, which revealed more uniform and consolidated structures when metakaolinite was added.