Salt weathering of sandstone at the Angkor monuments,Cambodia: identification of the origins of salts using sulfur and strontium isotopes

The Angkor monuments in northwestern Cambodia, which are primarily made of sandstone, are suffering from deterioration due to salt weathering. In order to elucidate the sources of the salts and salt weathering process, this paper analyzed bulk chemical compositions and S (sulfur) and Sr (strontium) isotopic ratios for the salts and surrounding environmental materials. At places where bats inhabit the structures, various kinds of sulfate and phosphate salts are formed on the surface of the sandstone. The results of the analysis demonstrate that the S and P (phosphorus) components in the salts are primarily derived from bat guano. Moreover, Ca (calcium), which is the major element in the salts, is suggested to be derived from both bat guano and the sandstone. The isotopic data strongly suggests that bat guano is related to salt weathering. Removal of these animal excrements is essential for future conservation of these monuments. On the other hand, exfoliation of sandstone commonly occurs due to crystallization of calcite (CaCO₃) on platform surfaces of pyramid-type monuments. A large amount of Ca in calcite is suggested to be derived from calcite cement of the building sandstone.     

北石窟寺表面防风化材料筛选

甘肃石窟分布广泛,洞窟大多开凿在砂岩上。在长期自然环境作用下,砂岩石窟表面风化严重,有部分区域甚至风化成砂土,砂岩石窟浅表层风化防治将成为重要的研究方向。本工作针对北石窟寺砂岩典型风化病害,选用0.5%羟甲基纤维素、5%砂岩加固材料、1.5%有机硅改性丙烯酸、1.5%丙烯酸、20%纳米SiO₂、10%正硅酸乙酯、3%PS共7种保护材料,基于室内试验测试这些材料的防风化性能,以加固前后宏观和微观特征进行定性描述,以色度、体积变化率、波速、表面硬度、抗压强度、透气性和吸水性作为加固定量评价指标,优选出砂岩加固材料、有机硅改性丙烯酸、纳米SiO₂、PS和正硅酸乙酯作为北石窟砂岩表面防风化加固建议材料。研究结果为北石窟寺砂岩质石窟表面防风化技术研发与应用积累了基础研究数据。