Effect of heat treatment and bedding orientation on the tensile properties of bedded sandstone

The effect of heat treatment and the bedding orientation on the tensile properties, the central strain and failure patterns of bedded sandstone specimens were studied under Brazilian test conditions. The laboratory test results show that the tensile strength decreases with increasing bedding orientation at different temperatures, which indicates the bedded sandstone possesses prominent anisotropy in tensile strength. The anisotropy coefficient first increases and then decreases with the increasing temperature. For all temperatures, both V-strain and S-strain present a decreasing trend with increasing bedding orientation. However, for all bedding orientations, the S-strain first increases and then decreases, but V-strain continues to increase with increasing temperature. Furthermore, the failure patterns of the failed specimens are generally classified into three categories: central across the bedding planes (CF), fracture along the bedding planes (LA) and the mixed fracture patterns of the two. Finally, the evolution of the internal structure of the disk specimens after different heat treatments was investigated by SEM tests. The specimen profile looks smoother and denser at 400oC and 600oC, but at 800oC and 1000oC, the internal structure of the specimen is sharply deteriorated by thermal reactions.