Simulation Experimental Study On Deterioration Of Carbonate Rock Surface Induced By Condensed Water In Longmen Grottoes

Longmen Grottoes is world-famous, which is13km away from the south of Luoyang city.lt existed about2300caves、10pagodas、3600stone blocks and more than100thousand statues. For colorful art of Longmen Grottoes, which provide important physical information for the study of Chinese Buddhist ancient history Sculpture and Sculpture arts.Longmen Grottoes was announced the first batch of key national heritage conservation units by the State Council in1961, and then in2000,it was inscribed on the World Heritage list.Longmen Grottoes has been suffering from the various natural and man-made destroying during its long history. After the liberation, the beginning of the Longmen Grottoes of conservation research, and completed a series of rescue works to improve the protection of the environment of the grotto. With further research, some new problems gradually aroused the concern of the researchers, one of the important problem is water damage to the Grottoes, seepage and condensation water. Water seepage has been more research and more mature control measures, the condensation water is only in its infancy stage. The Longmen Grottoes is mainly formed of the Cambrian limestone and dolomite which are very sensitive to acidic liquid. There are a series of acidic gaseous present in the atmosphere, such as CO2,SO2,NOx,etc that can produce erosion of cave rocks through condensed water.Supported by the National Natural Science Foundation project "experimental study on deterioration of carbonate rock surface of grotto induced by condensed water"(40972183),in this paper the changes of Longmen Grottoes micro-climate and deterioration of rocks induced by condensed water is researched and evaluated quantitatively.Found in previous analysis of the chemical composition of the residue after the Longmen caves condensation water air-dried, a large number of gypsum precipitation, while the results of the analysis in2010, the water quality of the field condensate also has a high SO42-composition, in order to study the condensation degradation of water on carbonate containing aqueous solution of SO42-in the room configuration, the sample immersion test, after the end of the trial, the deterioration analysis of samples of different lithology.Simulation experiments using the configuration SO42-in aqueous solution as a source of high humidity gas, condensate water, and then pass to the chamber into a certain amount of CO2gas, and water-gas-rock, three-phase coupling reactions in the chamber, after the end of the trial, the specimen mass loss, changes in porosity, corrosion depth, scanning electron microscopy, five degradation test of water quality analysis, and comparative analysis of the degradation of limestone and dolomite.This article by indoor simulation experiment, laboratory simulation of condensation water on deterioration of carbonate rocks, and quantitative analysis, provide the scientific basis for the protection of the Longmen Grottoes.According to the role of condensation of water on carbonate deterioration test and in the condensate, the CO2effect on degradation of carbonate rock of simulation test results, the following conclusions:(1)By summing up the duration of live condensation water in2005and2010, the longest duration of a condensed water of13days, so the test soak time of the election13days for a period of test. After each test cycle, the conductivity of the solution soak carbonate was continued to increase, increase about270us/cm.(2)After six cycles of testing, found carbonate porosity increases and quality loss, rock-like hardness also fell.0.0212-0.0224g limestone quality loss, lost0.0116-0.0142g dolomite, limestone mass loss of about1.49～1.93times the dolomite, porosity value of approximately1.53～2.09times of the dolomite. SEM picture you can also see, degree of deterioration than dolomite limestone. By the same comparison with different rock porosity deterioration found that micro-fracture development affects the degree of erosion of rocks.(3)In condensation water on deterioration test of carbonate rock, on the dissolution of limestone and dolomite depth calculated for fitting, condensation under the action of water,100years later, S042-on limestone dissolution of depth of0.119mm and dolomite for0.05947mm.(4)Limestone and dolomite of the soaking water quality analysis solution found, major ions in solution Ca2+, Mg2+concentration is different, and combined with scanning electron microscopy, mass loss experiment, revealing the mechanism of limestone and dolomite in corrosion of different.(5)Condensation water on deterioration of indoor simulation test of carbonate rocks, due to condensation of SO42-with high concentration in water, in order to more accurately simulate condensation under the action of water, the CO2effect on degradation of carbonate rock, resulting in condensation of water vapor using a water solution is configured with SO42-.(6)Conducted a total of13times the formation of condensation water test, at the same temperature, the greater the humidity test chamber, the greater the dew point temperature, the more prone to condensed water. Pass into the CO2collected condensed water than directly generate the electrical conductivity of the condensed water increase the120us/cm of CO2on the degradation of the carbonate rocks have a greater impact.(7)The simulations were carried out78times, totaling936hours, which leads to the concentration of CO2in3000～5000ppm, after testing in accordance with the mass loss, changes in porosity, corrosion depth, microstructure observation and water quality deterioration evaluation.(8) After78trials, the quality of limestone loss of0.0604～0.0703g,34%increase in porosity, dolomite mass loss.0278～0.0284g,17%increase in porosity limestone amount of mass loss of2.5times as dolomite, poreThe rate of change for the dolomite2.1times. SO42-deterioration test of carbonate rocks, limestone loss was1.93times that of the dolomite, also proved to CO2, limestone dissolution extent greater than the dolomite. From the scanning electron microscope pictures can also prove this conclusion.(9) Longmen Grottoes environment based on the laboratory simulation test results, the dissolution of limestone and dolomite depth of the fitting curve, calculation of100years after the dissolution depth, limestone dissolution is0.7439mm, the depth of dissolution of dolomite is0.2829mm. Much larger than the carbonate degradation of SO42-, CO2carbonate degradation stronger.This innovation:on the basis of previous experiments, the paper used in the experimental apparatus humidifier instead of the original environmental chambers. And the scene of the condensed water concentration in the indoor test configuration similar to the aqueous solution, applied to the condensed water carbonate degradation experiments. Deterioration evaluation, the use of corrosion depth and surface hardness as a new evaluation.