湿度循环对石窟砂岩孔隙中硫酸盐结晶过程的影响

Effect of humidity cycle on sulfate crystallization process in grotto sandstone pores

为研究湿度循环变化下硫酸盐结晶对砂岩的作用机理,在实验室分别对云冈石窟砂岩、大足石刻砂岩、乐山大佛砂岩进行了硫酸镁溶液和硫酸钠溶液的湿度循环劣化试验,将试样在盐溶液中浸泡至饱和后置于恒温恒湿箱中蒸发,蒸发过程中将相对湿度控制在30%和85%之间循环变化,并在循环过程中运用无损检测手段评价其风化程度。试验结果表明:(1)环境湿度循环变化会导致砂岩试样中的盐类所含结晶水发生变化。(2)在多次湿度循环后3种试样超声波速均出现下降,试样核磁共振T2分布曲线信号强度都出现上升,说明砂岩内部孔隙增多。(3)3次湿度循环后乐山大佛砂岩试样超声波速降至新鲜砂岩的80%左右,试样质量损失率为2.5%;大足石刻砂岩试样超声波速降至新鲜砂岩的95%左右,试样质量损失率为0.5%;云冈石窟砂岩试样未出现明显剥落。因此硫酸盐结晶膨胀作用对乐山大佛砂岩影响最大,对云冈石窟砂岩影响最小。(4)湿度循环下硫酸钠的结晶膨胀作用对砂岩的破坏程度大于硫酸镁。

In order to study the action mechanism of sulfate crystallization on sandstone under cyclic change of humidity,the humidity cycle deterioration test of magnesium sulfate solution and sodium sulfate solution was carried out on Yungang Grottoes sandstone,Dazu Rock Carving sandstone and Leshan Giant Buddha sandstone respectively in the laboratory.After soaking in salt solution to saturation,the samples were evaporated in a constant temperature and humidity box.During the evaporation process,the relative humidity was controlled between 30%and 85%cyclically,and the degree of weathering was evaluated by non-destructive testing methods during the cycle.The test results show that:(1)Cyclic changes of humidity lead to changes in the crystal water contained in the salts in the sandstone samples.(2)After multiple humidity cycles,the ultrasonic velocity of the three samples all decrease,and the signal intensity of the NMR T2 distribution curve of the samples all increase,indicating that the internal pores of the sandstone increase.(3)After 3 humidity cycles,the ultrasonic velocity of the Leshan Giant Buddha sandstone sample drops to about 80%of the fresh sandstone,and the mass loss rate of the sample is 2.5%;the ultrasonic velocity of the Dazu Rock carving sandstone sample drops to about 95%of the fresh sandstone,its mass loss rate is 0.5%;the Yungang Grottoes sandstone sample does not show obvious exfoliation.So the effect of sulfate crystal expansion on the Leshan Giant Buddha sandstone is the greatest,and the influence on the Yungang Grottoes sandstone is the least.(4)The degree of damage to sandstone caused by the crystallization expansion of sodium sulfate under humidity cycle is greater than that of magnesium sulfate.