| Stone Stone cultural relics are important parts of cultural heritage with diverse,widely distributed,and numerous characteristics.They play positive roles in recording social development and cultural exchanges,with high values.There have been many achievements in the disease mechanism and protection and restoration of stone cultural relics preserved in the open air,but there are few studies on stone cultural relics in a closed-semi-open humid environment that are mostly damaged by water and salt transport and salt crystallization.In order to better protect the porous silicate stone cultural relics in the humid environment,this paper takes the Royal Tomb of Wang Chien as the object,discussing the damage mechanism of salt in the humid environment,screening the reinforcement materials suitable for the humid environment,and proposing corresponding countermeasures for the in-situ protection based on the scientific understanding of the preservation environment,stone material,and the type of disease.The main contents are as follows:Firstly,the Royal Tomb of Wang Chien with its regional environment and microenvironment were studied,it was determined that the temperature in the tomb was room temperature,and the relative humidity was between 60%～100%,which belonged to the humid environment.The finite element model was used to build the temperature and humidity field of the burial chamber,and it could be seen that the temperature distribution of the main hall and the post chamber where the stone cultural relics were located was uniform,and the relative humidity distribution increased with the increase of height,and the east and west areas were larger than the central area.Using infrared thermal imaging and geological radar detection,it can be seen that the structure of the tomb is complete,there is no water seepage,cracks,or holes.Combined with the dew point temperature with the temperature on the wall,the liquid water appearing in the rainy season is condensation.Combined with water quality and air pollutant analysis,it can be seen that the sulfate of salt came from the stagnant water,seepage,and acid gas.X-ray diffraction and thin-section facies were used to analyze mineral composition.The main components of stone cultural relics are quartz,feldspar,and calcite as the cement.The crystal salts were sodium sulfate and calcium sulfate with the IC,Raman,FTIR,and SEM-EDS.Based on the type and distribution of deteriorations,the development of salt weathering was evaluated by using historical photos and high-precision 3D models.At 20℃,the stones from Jintang County were used for simulation experiments,with 1 mol/L Na2SO4 solution,saturated CaSO4 solution,mixed solution,and H2O in different values of relative humidity of open environment(RH45%),RH60%,RH75%,and RH100%.Basic physical properties,solution conductivity,macromorphology,microstructure,etc.,were used as criteria for the damage degree of salt weathering,water salt transport,and water vapor diffusion.The damage mechanism of salt in a humid environment was studied.The salt weathering simulation experimental results show that the damage degree of the mixed solution is greater than that of the Na2SO4 solution at the same humidity.In the case of the same salt solution,the lower the ambient humidity,the easier it is for crystal salts to precipitate on the surface,and when soaked again,Na2SO4 dissolves to produce pressure,and then aggravate damage.The degree of damage is in an open environment>RH60%>RH75%.The higher the moisture content,the faster the mechanical properties of the sandstone deteriorate.The experimental results of water and salt transport show that under the condition of salt solution replenishment,the ambient humidity affects the evaporation rate and the position of salt crystallization,and the damage degree of salt crystallization efflorescence of the surface layer is less than the subsurface layer.Using the same salt solution,mirabilite is precipitated under the surface at RH75%.At RH60%,thenardite mostly accumulates on the surface of the stone.When the environment is open,after the crystalline salt shell is formed on the surface,the evaporation rate is reduced,and the salt crystallization position changes to the lower surface layer.The degree of damage is open environment>RH 75%>RH60%.Under the same humidity,CaSO4 blocked pores to reduce the drying rate with the low solubility,and Na2SO4 crystallized on the rock surface and the lower surface layer.Because of the hygroscopic salts,CaSO4 migration was promoted,and the crystallization position changed.The degree of destruction of the mixed salt solution was greater than that of the Na2SO4 solution.The water vapor diffusion study shows that the flux of the water vapor diffusion is positively correlated with porosity,and increases with the value of humidity difference.The water vapor diffusion coefficient is positively correlated with porosity,not with humidity.In a high-humidity environment,the stone absorbs moisture to form a gas-liquid interface,and water vapor diffusion is accompanied by condensation and evaporation,showing a trend that the diffusion coefficient increases with increasing relative humidity.Under the action of CaSO4 and Na2SO4,the stone relics of the Royal Tomb of Wang Chien continued to develop salt weathering.With the same degree of weathering,the higher the relative humidity was,the warping height greater.This depth of the stone in the tomb is the area frequently affected by the diffusion of water vapor.Due to the high humidity of the tomb,the crystalline salt may deliquescence,and the condensate dissolves the surface crystal salt in the rainy season,resulting in the aggravation of salt weathering.Taking the curing and cracking as the standards,the applicability of TEOS/SF016,TEOS/HDTMS,TEOS/N-octylamine,TEOS/PDMS-OH,TEOS/n-HA,Remmers KSE 300,and nmCa(OH)2 were initially screened in a humid environment.The material properties were based on water absorption,air permeability,permeability,chromaticity,wave velocity,surface hardness,and water static contact angles.The salt resistance of the material was evaluated by salt crystallization weathering cycles.The TEOS/n-HA has good overall performance.It can be used for fragile stone cultural relics in high humidity or the environment with condensate.Based on the environmental and micro-environment characteristics of the Royal Tomb of Wang Chien,the degree of salt weathering of cultural relics,and the source of salt,some protection countermeasures for stone cultural relics were proposed,such as desalination,reinforcement,and environmental control. |
