6.2 Experimental parameters and analytical method
All samples were first dried at 105 ℃ for at least 48h, and cooled down
until a constant mass was reached. After that, the mass, surface
hardness and P-wave velocity were measured and the surface
microstructure of samples was photographed at fixed points using a
microscope. For each sample, all these parameters were re-determined
after every period. At the end of the experiments, the XRD and SEM of
samples were measured in order to analyze the sandstone weathering
mechanism. Fig.8 shows that the sampling locations of XRD and SEM are
the surface (red), middle (blue) and inner (green) parts. Three
experiments were conducted in 50 periods that lasted for 350 days.