风化砂岩石窟表面热响应及力学性能变化:对砂岩石窟本体表层风化(劣化)评价的启示

Surface thermal response and mechanical property changes of weathered sandstone rock-hewn cave temples:implication for the evaluation of surface weathering(deterioration)

表层风化问题严重影响石窟寺类文物的长久保存。如何通过风化表层的性能变化来对石窟寺进行病害诊断和风险评估是预防性保护的关键问题。本研究利用便携式无损检测手段(ProceqEquotip 550里氏硬度计、FLIR T660红外热成像仪)对甘肃庆阳北石窟寺外立面8个研究面进行表面硬度测试及表面温度监测,分析其典型风化病害的热响应情况及力学性能变化规律。研究结果显示,病害类型对其表面硬度值和温度波动幅度有不同程度的方向性影响。水锈结壳的表面昼夜温度波动幅度最小,表面硬度离散地分布在较高水平;粉化剥落和泛盐的表面昼夜温度波动较平缓,表面硬度值集中分布在较低水平;沟槽状溶蚀(差异风化)的表面昼夜温度波动幅度略高于粉化剥落表面,其表面硬度集中分布在较高水平;微生物覆盖的表层,昼夜温度波动幅度最大,表面硬度值离散地分布在较低水平。上述病害-性能对应关系有助于在石窟寺类文物的日常监测中判别风化病害的分布及变化趋势,对砂岩石窟的风险预警有一定指示作用。

Near-surface weathering is a crucial problem threatening the preservation of rock-hewn cave temples.Erosion pattern evaluation and risk assessment through property variation of the weathered surface is a vital point that needs to be addressed for preventive conservation.In this study,we used portable non-destructive testing instruments(ProceqEquotip 550 Leeb hardness tester,FLIR T660 infrared thermal camera)to measure surface hardness and to monitor the surface temperature of 8 studied surfaces on the facade of the North Grotto Temple in Qingyang,Gansu Province.Based on the in-situ measurement,we studied the thermal response and property changes of the typical weathering patterns.The study results show that different weathering patterns could directionally affect the magnitude of surface hardness and the range of temperature fluctuation to some extent.The diurnal temperature of the crust surface fluctuated within a minor degree,and the surface hardness was broadly dispersed at a high range of value.The diurnal temperature fluctuations of the powdering surface and salt efflorescence surface were relatively gentle and flattened,and their surface hardness values were centralized at a low level.The diurnal temperature fluctuation of the groove-like erosion(differential weathering)surface was slightly greater than that of surfaces with powdering and salt efflorescence,and the surface hardness was centralized at a higher level.Surfaces covered with microorganisms had the most extensive range of diurnal temperature fluctuation,and scattered surface hardness values were distributed at a low level.Given the above evidence,the relationship between weathering patterns and properties can not only help with the distinguishing of distribution and developmental trends of weathering patterns in daily monitoring but also has an indicative effect on the risk warning of rock-hewn cave temples.