Sandstone weathering in tropical climate: Results of low-destructive investigations at the temple of Angkor Wat, Cambodia

Investigations at the temple of Angkor Wat aimed at the explanation of the major weathering processes of building sandstone as well as at the role of both intrinsic factors (i.e. sandstone petrography and properties) and extrinsic factors (i.e. climatic and environmental influences). Since material sampling at the temple was limited to a few boreholes because of the high artistic rank of the building, non-destructive and low-destructive in-situ investigation methods like ultrasonic wave and drilling resistance measurements had to be applied to obtain information about the material properties of sandstone and their changes due to weathering. Moreover, hydric swelling behaviour of the sandstone was determined on undecorated pieces of fallen blocks from the walls. Additional random-test stable isotopic investigations of environmental influences and salts and thorough investigations of the spatial distribution of salts in the ashlars at two selected places with typical weathering patterns completed the set of data.The results demonstrate that the weathering process is mainly triggered by rain–dry-cycles. Salt load found in the stone is composed of gypsum and nitrate compounds. Sulphur stable isotope investigations of potential sources of gypsum lead to the conclusion that soluble components of bat droppings are the major source of salts. Influences of environmental factors like sulphate in rainwater or SO2 from the air on salt formation are unlikely. Gypsum may reinforce the surface deterioration due to high swelling–shrinking movements of the sandstone (> 1 mm/m) during intensive wetting–drying cycles.