4.0 Introduction
Dazu Rock Carvings can be perceived as an example of the highest level
of Chinese cave temple art from the 9th to 13th centuries. The United
Nations Educational, Scientific and Cultural Organization (UNESCO)
designed them as the world cultural heritage in December 1999. In
particular, the Niche of Sakyamuni Entering Nirvana constructed of
sandstone is the largest bust of Sakyamuni in the world, and also an
important part of Dazu Rock Carvings (Tong, 2003). It has suffered from
extensive surface weathering over the past 1000 years. The surface
weathering diseases include efflorescence, granular disintegration,
biological colonization, cracks, seepage, scaling, blistering and
missing parts, and granular disintegration in total dominates that.
Therefore, the formation and mechanism of granular disintegration is the
research object of the studied statues.
Until lately, the study on granular disintegration adopts on-site
investigation and description as the key study approach. Traditionally,
the development of granular disintegration on rock surfaces can be
attributed to physical weathering such as dry-wet cycle; freeze-thaw
cycle and salt crystallization due to water absorption and temperature
(Rodriguez-Navarro, Linares-Fernandeza, Doehneb, & Sebastian, 2002;
Cardell et al., 2003; Oguchi & Yuasa, 2010; Labus & Bochen, 2012); and
chemical action including dissolution, oxidation, reduction and
hydrolysis (Prieto, Silva, Rivas, Wierzchos, & Ascaso, 1997; Pera,
Arribas, Critelli, & Tortosa, 2001; Herrera, Arroyave, Guiamet, de
Saravia, & Videla, 2004; Lee, Jo, & Kim, 2011). However, Ilieş,
Irimuş, and Rus (2015) pointed out that over-reliance on field
observations limited our understanding of the granular disintegration
formation. Recognition of this limitation is implicit in many studies
which sought to determine physical and mechanical parameters from the
macro level, including, e.g., mechanical strength, porosity, ultrasonic
velocity, mass and water absorption (Jeng, Lin, & Huang, 2000; Tan,
Chen, Yang, & Cao, 2011; Özbek, 2014). Nonetheless, few micro level
studies were conducted using indirect methods, e.g., XRD, SEM and
chemical analyses. They can be usefully complemented by (1) providing
direct evidence of cracks and pores in rocks and their constituent
grains; and (2) analyzing mineral and chemical composition to evaluate
their potential contributions towards rock deterioration (Clément &
Kimpe, 1977; Pye & Cambridge, 1985; Sassoni & Franzoni, 2014).
Since the 1990s, some studies have been conducted to understand the
weathering effects on Niche of Sakyamuni Entering Nirvana. These studies
include preserving environmental and meteorological characteristics
(Zhou & Deng, 2002; Chen, Jiang, & Xi, 2004); effect of the water
seepage (Wang & Zhang, 1992; Zhang & Jiang, 2016); hydraulic
parameters and seepage model of rock (Wang, Wang, & Zhang, 1999; Wang,
Wen, Wang, & Zhang, 2001); prevention of water hazard and destruction
mechanism of Na2SO4 crystals on
sandstone by laboratory accelerating ageing experiments (Tan, 2013);
surface weathering characteristics and degree of sandstone (Zhang et
al., 2018). However, the relation between granular disintegration and
sandstone weathering mechanism has not been revealed experimentally.
In this study, we conducted three weathering experiments to examine
different influences on sandstone weathering of Niche of Sakyamuni
Entering Nirvana. From these experiments, we
analyze
the changes in physical and mechanical properties of sandstone and the
sandstone weathering mechanism. The research outcomes could provide some
physical and mechanical parameters and basis for the protection of the
studied statues.