Experimental Study On The Effect Of The Sulfate On The Weathering Of Glutenite In Maijishan

Due to the action of water seepage and salinity action,the cliff of Maijishan grottoes appears the phenomenon of pulverization,peeling and even peeling.The present paper is based on the document of the State Administration of Cultural Heritage of China that"about Maijishan grottoes reinforcement and ooze water management of the second phase of the project approval”?cultural relics undertaking[2015]No.718?.Based on the study of the basic properties of the glutenite in maijishan grottoes,the capillary migration of MgSO₄ and Na₂SO₄ solution with mass fraction of 5%and cyclic degradation of the glutenite core samples taken from the test area were carried out in laboratory,respectively.During the test,parameters such as the capillary migration height of salt solution,rock sample quality,elastic wave velocity and compressive and tensile strength of rock sample were measured.The migration,crystallization accumulation,macroscopic and microscopic characteristics of the two salt solutions and their differences were analyzed.The theoretical crystallization pressure of the two salt solutions during cyclic degradation test was calculated.The following conclusions can be drawn:?1?The X-ray diffraction test,the particle density and block density test,the water absorption test and saturation water absorption test,and the uniaxial strength test were carried on the rock samples taken from the Maijishan grottoes.The results show that the mineral composition of the glutenite of Maijishan grottoes is mainly quartz,feldspar,calcite and clay minerals,etc.In addition,it also contains a small amount of mica.The clay mineral is mainly the mixture with illite and montmorillonite.Mineral particles vary in size and the sorting characteristics are poor.The cementation mode is argillaceous cementation.The average rock particle density and block density are 2.66g/cm³ and 2.40g/cm³,respectively.The average water absorption in the dry state is 2.19%and the average saturated water absorption was3.23%.The average compressive strength and tensile strength of the rock are11.67MPa and 0.8MPa,respectively.?2?The migration regularity of the two salt solutions in the glutenite is greatly different due to the environmental influence and the different salinity.The results show that,In the open environment,the height of the capillary front of MgSO₄solution with mass fraction of 5%is positively correlated with time in the glutenite.The migration rate fitted is 5.58×10^-5cm/s;The migration of Na₂SO₄ solution with a mass fraction of 5%in the conglomerate is characterized by multi-order nonlinear curves.In the sealed environment,the migration height of MgSO₄ and Na₂SO₄solution showed a positive correlation trend with time,and the fitting rate was 7.24×10-⁵cm/s and 7.19×10^-5cm/s,respectively.?3?During the migration of salt solution,if there is evaporation of water in the external environment,the concentration of salt solution will increase,and crystals will appear when it reaches supersaturation.Observation of the surface characteristics of rock samples during the experiment shows that,under the action of water evaporation,the two solutions will crystallizate during migration,but the characteristics of crystallization accumulation are different.MgSO₄ mainly crystallizes and concentrates in the inner part of the rock sample,while the salt accumulation on the surface of the rock sample is less.Na₂SO₄ mainly is enriched on the surface of rock samples,and the quantity of crystals is relatively large,with a wide distribution area.In the early stage of water evaporation,large area Na₂SO₄ crystals with large water content were gradually formed on the surface of the rock sample,while in the late stage of water evaporation,salt crust was gradually formed from the upper part of the rock sample to the lower part.?4?There are differences in the microscopic and macroscopic failure characteristics and timeliness of the two salts on the conglomerate.The observation experiments under the Environmental Scanning Electron Microscope show that MgSO₄ mainly causes the"radiative"fractures to occur near the mineral surface inside the glutenite,and increasing the porosity of the rock as a whole.Na₂SO₄ is attached to the pores on the rock surface,and with the increase of quantity and volume,the mineral surface is gradually pulverized.In the macro state,MgSO₄ is relatively weak in the surface of the glutenite,mainly producing cracks in the interior.The crack gradually expands to the surface of the sample.Na₂SO₄ is enriched on the rock sample surface.The rock sample surface was powdering and spalling because of crystalling,The process was carried out from the outside to the inside and from the top to the bottom.Moreover,based on the macroscopic characteristics and the degree of reduction of each parameter value,it was found that Na₂SO₄ destroys the glutenite more rapidly than MgSO_4.?5?By using Corren equation,the theoretical value of crystallization pressure of two salt solutions in the process of cyclic degradation test is calculated.The results show that the samples under Na₂SO₄ solution cycle degradation begin to generate crystallization pressure during the 2th to 3th cycle,and the theoretical crystallization pressure value gradually increases with the increasing of cycle times.The theoretical crystallization pressure value is 33.4MPa after 6th cycles,.The rock samples under the action of MgSO₄ solution do not produce crystallization pressure in the first 7 cycles of deterioration.The theoretical crystallization pressure is generated during the 8th to9th cycles.The specific value is 9.94MPa.