9.0 Conclusions
The physical and mechanical properties of sandstone (sampled from Niche of Sakyamuni Entering Nirvana) as a function of dry-wet cycle, freeze-thaw cycle and acid rain cycle were weakened using a series of tests on a macro-scale. The mineral, chemical compositions and microstructure deteriorated on a micro-scale. The conclusions are:
(1) The main deterioration is granular disintegration under different weathering conditions. The sandstone weathering is more significant on sandstone with bedding development, and the weathering rate escalates with various numbers of cycles.
(2) The variation in mass is attenuated by an exponential function, while the variations in surface hardness and P-wave velocity are attenuated by a power function. Besides, the approximate value of weathering rate is derived from the variation in surface hardness and P-wave velocity.
(3) The deterioration degrees affecting the sandstone weathering follow this order: acid rain cycle, freeze-thaw cycle, dry-wet cycle. Notably, higher H+, concentrations would enhance the sandstone weathering. To control the harm of acid rain, antiseptic materials should be applied on the statue surface.
(4) The deterioration of sandstone by water occurs from the surface to the inner structure. The surface structure of sandstone is the most susceptible to weathering effect. The dissolution of calcareous cement, alteration of feldspar, and water swelling and drying shrinkage of smectite on account of moisture change make the sandstone surface loose, and the grains are taken away by water, leading to the granular disintegration. SEM demonstrates that granular disintegration is primarily driven by the widening inter-granular micro-cracks.
(5) In this paper, the weathering effects of sandstone of Niche of Sakyamuni Entering Nirvana were studied experimentally. However, laboratory experiments were limited by time period, and the sandstone weathering effects of studied statues is longer and more intense. The research is thus intended to experiment for a long time.