7.1 The deteriorated features
Samples as a result of 50 periods of three experiments were deteriorated
(Figs. 9, 10, 11). The results demonstrate that the most severe
deterioration was driven by acid rain cycle. With increasing periods,
many granules fell off and yellow spots were visible. By contrast,
samples did not deteriorate in the dry-wet and freeze-thaw cycles
(despite a small amount of granules fell off.). Hence one main type of
failure is observed in all of the samples, i.e., granular
disintegration.