7.2 Surface microstructure
The surface microstructure of samples at 60 times in three experiments
was shown in Fig. 12, 13, 14. Quartz, feldspar and other grains of fresh
sandstone were closely arranged. The grains were filled with white
cement with clear boundary contour and smooth surface. As the experiment
went on, all samples experienced granular disintegration. On the other
hand, the surface color of samples turned dark and black spots were
visible. Besides, a small number of pores and micro-cracks reflected
that the structure got loose. Some yellow spots appeared on the samples
under the effects of acid rain cycle. The deterioration of samples in
acid rain solution (especially at higher H+
concentrations) was more serious and rapid than that of samples affected
by dry-wet and freeze-thaw cycles.