Deterioration Test Of Soluble Salt On Sandstone Of Dazu Rock Carvings

Deterioration of rock caused by salts is very common in nature. The expansion force, from the crystallization process of these dissolved salts, destroys the internal structure of rock. Researches show that the soluble salt is an important factor of weathering and types of soluble salts distribute widely in the Dazu Rock Carvings.Based on existing inverstigations, the crystallination process have been simulated by controlling the temperature and relative humidity in environmental chamber, this has been used to study the destruction procedure and manner of Na2SO4crystal. The whole researches were composed by two sections, the anhydrous sodium sulfate experiment and the sodium sulfate decahydrate experiment. In the anhydrous sodium experiment, the temperature was set at35℃and relative humidity was set at40%. In the mirabilite experiment, the temperature was set at10℃and relative humidity was set at90%.Some conclusions have been drawn:1. By analyzing the changes of surface and shape of the rock sample during the experiment, failure mode of the rock by Na2SO4crystallization can be obtained. Failure modes of anhydrous Na2SO4crystal samples are mainly as follows:flakjing off, loosing particles, damage along the crack surface. Failure modes of Na2SO4·10H2O crystal samples are not so obvious, as follows: the crisp destruction at samples’ end, Guzhang, damage along the weak surface.2. Monitoring the deformation of the rock samples when they were placed in environmental chamber with a high sensitivity probe, the deformation change trend of the rock samples can be found. In Anhydrous Na2SO4experiment, the rock samples’ deformation mainly reflects as volume shrinkage, and the amount of shrinkage increases with the increasing number of cycles. But in the Na2SO4·10H2O experiment, the rock samples’ deformation mainly reflects as volume expansion, and with the increasing number of cycles, the amount of expansion increases.3. Testing the two elastic wave velocities of saturated and crystallized sodium sulphate of each circulation process, and analysing the change trend of those two wave velocities, it is found that, the two wave velocities of laboratory samples both show sharply decline trend in Anhydrous Na2SO4experiment. Though, the two velosities of Na2SO4·10H2O samples can be divided into three parts, a momentary rising at first, then, following a long term stable phase, at last rapid decline before destruction. 4. By testing and analysing the two quality index (quality idex of samples saturated by saturated Na2SO4solution and crystallized sodium sulphate in enviornmental chamber) of each circulation process, it is discovered that, two quality index of andydrous Na2SO4samples both show rapid rising at1st circulation (minority samples maintain the trend to2nd circulation), after that these two quality index declined sharply:meanwhile, just like wave velosities situation, the two quality index of Na2SO4·10H2O samples can be divided into three parts too, a momentary rising at first, and then a long term stable phase, at last rapid decline before destruction.5. According to the data of uniaxial compressive strength test of the rock sample, the strength rule can be concluded:both mirabilite experiment and anhydrous sodium experiment, the strength of rock samples would reduce gradually with cycles increasing.6. SEM was taken on the rock samples, which were fresh and at different cycles, to contrastive analysis the effect of Na2SO4crystal on the rocks’ microstructure. The experiment results shows that with the process of cycles, the pores within rock sample gradually more increases, the structure becomes loose, and the content of Na2SO4crystals within the rock sample increases.The simulation tests show that the deterioration induced by repeated crystallization of Na2SO4should not be ignored in prorosity sandstone and there are distinct effects of different phase of Na2SO4.