大足石刻小佛湾造像砂岩室内模拟劣化试验研究

风化是当前大足石刻小佛湾造像砂岩最为严重的病害之一,基于造像赋存环境设置3组室内模拟劣化试验:干湿循环、冻融循环(饱水组和干燥组)和酸雨循环试验(pH=2.6,4.1,5.6),进行45个循环周期试验研究,历时320 d,以此模拟小佛湾造像砂岩的风化过程。在试验前以及每个试验周期后,量测试样质量、表面硬度和纵波波速进行风化程度检测,并通过显微拍照(60倍)观察试样表层微观结构特征。最后对试样进行X射线衍射(XRD)、扫描电镜(SEM)和表面吸水性测试来分析劣化机理,并通过色差测试来检测表面颜色变化。试验结果表明:砂岩的主要破坏方式为粉化剥落。砂岩原生层理和泥质团块最先受风化作用的影响。砂岩的质量、表面硬度和纵波波速呈逐渐下降趋势。水对砂岩的破坏是由表及里依次进行的。酸雨循环对砂岩的破坏最严重,冻融循环次之,干湿循环最小。因此,此次研究成果将为大足石刻小佛湾造像的保护提供依据。

Experimental study on indoor simulated deterioration of sandstone of Xiaofowan statues at Dazu Rock Carvings

The sandstone of Xiaofowan at Dazu Rock Carvings in China has severe weathering. To solve this problem, three experiments are set up based on the local environment: wetting-drying cycles, freeze-thaw cycles (saturated group and dry group) and acid rain cycles (pH=2.6, 4.1, 5.6). In this study, the mass, surface hardness and P-wave velocity are measured to explore the weathering degree of sandstone over multiple experimental cycles (for a total of 45 periods, 320 days), and the surface microstructure of the sandstone is photographed (60 times). The X-ray diffraction (XRD), scanning electron microscope (SEM) and water absorption are executed to analyze the weathering mechanism of sandstone. The color change is detected through the color difference tests. The experimental results show that the main damage phenomenon of the sandstone is granular disintegration. The primary bedding and argillaceous mass of sandstone are first affected by weathering. The mass, surface hardness and P-wave velocity of the sandstone gradually decrease. The damage by water is performed on the sandstone from the surface to the inside. The damage degrees affecting the sandstone weathering are in turn as follows: acid rain cycles, freeze-thaw cycles, wetting-drying cycles. Therefore, the results of this study may provide a basis for the protection of Xiaofowan statues at Dazu Rock Carvings.