可溶盐对云冈石窟砂岩劣化试验及模型建立

Deterioration experiment with soluble salt on sandstone of Yungang grottoes and its model creation

可溶盐富集是造成山西大同云冈石窟砂岩表面风化、结构破坏及强度降低的重要地质病害之一。采取云冈石窟造像层砂岩,使用芒硝对该砂岩进行了劣化模拟试验。在可溶盐反复结晶过程中,对样品进行实时变形监测,并对循环过程中质量衰减、强度变化、孔隙分布等进行测试与分析。结果表明,可溶盐的发育是导致石窟表面粉化脱落的重要因素,严重降低了石窟文物本体的价值;可溶盐结晶导致岩石颗粒间胶结作用破坏,增大岩石孔隙率,岩石内部结构劣化严重影响岩石的刚度与强度等力学参数;对比无水芒硝与10水芒硝两种劣化试验,云冈石窟在相对干燥季节下,可溶盐晶体发育对岩石破坏更为显著。为了预测砂岩长期劣化过程,在试验数据基础上,初步建立起孔隙增长的对数模型和强度衰减的指数模型。

Soluble salts is a critical disease for Yungang grottoes of Datong city in Shanxi province, which leading to the surface weathering strengthen reduction and structure damage. An experiment of deterioration simulation with sodium sulfate has been carried out for the sandstone taken from the sculptures distribution layers. The deformations of samples have been real time monitored and the mass loss, strength decrease and pore character change, and etc. have been tested during the salt crystallization cycles. Following conclusions have been obtained. Firstly, the injury of the soluble salts is the main reason for the powdered form on the sand rock surface, which cause the historical value is fading away. Secondly, the inner structure has been changed and the glue materials have been destroyed by the crystalline of the salts inside the rock, the consequence is the porosity ratio increase and stiffness and strength decrease. Lastly, in the dry season, the deterioration effect of soluble salt on rock should higher than other time from the comparative of two phases simulation tests, thenardite （Na2SO4） and mirabilite （Na2SO4＂ 10H20）. For long term prediction of the deterioration action of salts, a logarithm model has been used for porosity increase and an exponent model for strength decrease.