Study On The Mechanical Properties Of The Sandstones Of Rock Paintings In Helan Mountain By Dry-Wet Cycles In Acidic Environment

Helanshan mountian paintings are immovable stone artifacts that have long been associated with the natural environment and have caused severe weathering.For this reason,this article takes the typical carrier sandstones(referred to as A,B)in the Helan Mountain rock relic cultural area as the research object,and carries out a series of experiments in light of the actual environment in which it has occurred.Firstly,the carrier sands A and B were soaked in water chemical solutions of PH=7.0 and PH=2.0,respectively,and after 0,5,10,20,50,and 60 dry-wet cycle times,changing law of water absorption of two kinds of sandstones.The experimental result shows that the higher the acidity and the more frequent the wet and dry cycles,the higher the water absorption rate of the two types of carrier sandstones.The water absorption rate of Class A sandstones is more sensitive to the number of chemical solutions and the number of wet and dry cycles;the sandstone of Class A is at PH=7.0 The water absorption rate increased by 4.74 times;it increased by 5.36 times at PH=2.0;the water absorption of Class B sandstone increased by 4.71 times at PH=7.0 and 6.02 times at PH=2.0.Secondly,the uniaxial compressive strength and uniaxial tensile strength tests of two types of carrier sandstones under different chemical solutions and cycles of dry-wet cycle times were carried out to explore the deterioration rules,the experimental result shows that the uniaxial tensile strength and compressive strength of sandstones A and B in the solution of PH=2.0 are the most obvious.The strength of Class A sandstone has dropped by 70.59%and 73.52%,respectively,and that of Class B sandstone has dropped by 53.68%and 69.29%respectively.and then from the microstructure,scanning electron microscope(SEM)was used to perform two types of tests,using the theory of chemical thermodynamics,the degradation process of carrier sandstone in Helan Mountain was analyzed.The experimental result and analysis show that with increasing the dry-wet cycle times,the micro structures of sandstone are looser,and the spatial distributions of particles are more uneven,which is consistent with the results of strength change of macro tests.It is analyzed the test process from the perspective of chemical thermodynamics to verify the accuracy of the test results.Therefore,dry-wet cycles is an important influencing factor that can not ignored when stone relics are affected by water.The results will provide theoretical basis for mechanism of deterioration?post-protection and restoration of Relics of Rock paintings in NingXia Region.