壁画地仗中盐分的毛细输送机制研究
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摘要
设计了专门的毛细水输盐模拟试验装置,在精确控制温度、湿度和供水水头的情况下,监测不同孔隙溶液在含盐及脱盐澄板土地仗中的毛细迁移特征。水盐迁移前后,测定模拟地仗的导热系数、孔隙半径变化,从微观角度判断外来盐分及地仗内存在的盐分对地仗盐害的贡献。试验结果表明,溶液毛细迁移速率由大到小排列为KCl与Na_2SO_4混合溶液>KCl溶液>Na_2SO_4溶液>H_2O。毛细上升速度随着试样高度的增加逐渐减慢,而且脱盐澄板土中的毛细上升速率大于天然澄板土中的速率。孔隙溶液电导率随试样高度增加呈递增趋势,且天然澄板土试样的电导率普遍高于脱盐澄板土。试样的导热系数随高度的增加出现先减小后增加的总体趋势。脱盐澄板土与天然澄板土相比,孔径分布密度偏向小孔径方向;当迁移溶液为混合盐时,孔径分布较单一盐溶液时集中。模拟试验结果发现,毛细输送的外来盐分(特别是硫酸盐和氯化物复合盐)造成的土体盐胀破坏比土中既有盐分更加显著,说明控制降水入渗引起的化学淋滤作用对预防顶层洞窟壁画盐害具有重要意义。
In this study a device has been developed to simulate the capillary water and salt migration. The pore solution migration in the desalinated and pure Dengban soils can be monitored under the temperature-, humidity- and water head-controlled conditions. Before and after the capillary test, thermal conductivity and pore radius of the specimens are determined to estimate the contribution of external and internal salts to the salt damage of mural from the microscopic viewpoint. The experimental results show that solution migration rate decreases in the order of mixed KCl and Na_2SO_4 solution ? KCl solution ? Na_2SO_4 solution ? distilled water. The capillary rise rate decreases gradually with the specimen height, and the capillary rise rate in desalination Dengban soils is greater than the pure Dengban soils. The electric conductivity of soil solution increases vertically with the soil specimen height, and the conductivity of pure Dengban soil is greater than that of desalinated Dengban soil. The thermal conductivity of the soil specimens shows an overall tendency that increase first and then decrease with the rising specimen height. Compared with the pure Dengban soil, the pore-size distribution density of the desalinated Dengban soil reduces to a small aperture. In the case that the mixed salt solution is transported in soils, and pore sizes are concentrated in a more narrow area than that if single salt solution is used. It is shown that the salts transported by capillary, especially mixed sulfate and chloride, induce more severe damage than the salts contained in the soil, indicating that it is important to prevent rain water from leaching into upper caves for mural conservation.
In this study a device has been developed to simulate the capillary water and salt migration. The pore solution migration in the desalinated and pure Dengban soils can be monitored under the temperature-, humidity- and water head-controlled conditions. Before and after the capillary test, thermal conductivity and pore radius of the specimens are determined to estimate the contribution of external and internal salts to the salt damage of mural from the microscopic viewpoint. The experimental results show that solution migration rate decreases in the order of mixed KCl and Na_2SO_4 solution ? KCl solution ? Na_2SO_4 solution ? distilled water. The capillary rise rate decreases gradually with the specimen height, and the capillary rise rate in desalination Dengban soils is greater than the pure Dengban soils. The electric conductivity of soil solution increases vertically with the soil specimen height, and the conductivity of pure Dengban soil is greater than that of desalinated Dengban soil. The thermal conductivity of the soil specimens shows an overall tendency that increase first and then decrease with the rising specimen height. Compared with the pure Dengban soil, the pore-size distribution density of the desalinated Dengban soil reduces to a small aperture. In the case that the mixed salt solution is transported in soils, and pore sizes are concentrated in a more narrow area than that if single salt solution is used. It is shown that the salts transported by capillary, especially mixed sulfate and chloride, induce more severe damage than the salts contained in the soil, indicating that it is important to prevent rain water from leaching into upper caves for mural conservation.
引文
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[21]王全九,邵明安,郑纪勇.土壤中水分运动与溶质迁移[M].北京:中国水利水电出版社,2007.WANG Quan-jiu,SHAO Ming-an,ZHENG Ji-yong,et al.Water movement and solute transport in soils[M].Beijing:China Water&Power Press,2007.
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[23]RIJNIERS L A,PEL L,HUININK H P,et al.Salt crystallization as damage mechanism in porous building materials——A nuclear magnetic resonance study[J].Magnetic Resonance Imaging,2005,23(2):273-276.
[24]CHAROLA A E.Salts in the deterioration of porous materials:An overview[J].Journal of the American Institute for Conservation,2000,39(3):327-343.
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[27]邓友生,何平,周成林.含盐土导热系数的试验研究[J].冰川冻土,2004,26(3):319-323.DENG You-sheng,HE Ping,ZHOU Cheng-lin.An experimental research on the thermal conductivity coefficient of saline soil[J].Journal of Glaciology and Geocryology,2004,26(3):319-323.
[28]SCHERER G W.Stress from crystallization of salt[J].Cement and Concrete Research,2004,34(9):1613-1624.
[2]ANGELI M,BIGAS J P,BENAVENTE D,et al.Salt crystallization in pores:Quantification and estimation of damage[J].Environmental Geology,2007,52(2):205-213.
[3]ZEHNDER K.Long-term monitoring of wall paintings affected by soluble salts[J].Environmental Geology,2007,52(2):353-367.
[4]LBPEZ-ACEVEDO V,VIEDMA C,GONZALEZB V,et al.Salt crystallization in porous construction materials,II.Mass transport and crystallization processes[J].Journal of Crystal Growth,1997,182(1-2):103-110.
[5]WINKLER E M,SINGER P C.Crystallization pressure of salt in stone and concrete[J].Geological Society of America Bulletin,1972,83(11):3509-3513.
[6]LARSEN P K.Desalination of a painted brick vault in Kirkerup Church[C]//Proceedings of ICOM-CC 12th Triennial Meeting Lyon 29.[S.l.]:[s.n.],1999,II:473-477.
[7]张明泉,张虎元,曾正中,等.莫高窟地仗层物质成分及微结构特征[J].敦煌研究,1995,(3):23-28.ZHANG Ming-quan,ZHANG Hu-yuan,ZENG Zheng-zhong,et al.Material composition and micro-structure characteristics of the plaster at Mogao Grottoes[J].Dunhuang Research,1995,(3):23-28.
[8]王旭东,郭青林,李最雄,等.敦煌莫高窟洞窟围岩渗透特性研究[J].岩土力学,2010,31(10):3139-3143.WANG Xu-dong,GUO Qing-lin,LI Zui-xiong.et al.Research on permeability of surrounding rock at Dunhuang Mogao Grottoes[J].Rock and Soil Mechanics,2010,31(10):3139-3143.
[9]张明泉,张虎元,曾正中,等.莫高窟壁画酥碱病害产生机制[J].兰州大学学报(自然科学版),1995,31(1):96-101.ZHANG Ming-quan,ZHANG Hu-yuan,ZENG Zheng-zhong,et al.The mechanisms of efflorescent disaster of wall-paintings in Mogao Grottoes[J].Journal of Lanzhou University(Natural Science Edition),1995,31(1):96-101.
[10]陈港泉,于宗仁.莫高窟第351窟壁画疱疹和壁画地仗可溶盐分析[J].敦煌研究,2008,(6):39-49.CHEN Gang-quan,YU Zong-ren.Test for blister and soluble salt in powdering and the layer of plaster for the wall-painting in Cave 351 at Mogao Grottoes[J].Dunhuang Research,2008,(6):39-49.
[11]郭青林,王旭东,薛平,等.敦煌莫高窟底层洞窟岩体内水汽与盐分空间分布及其关系研究[J].岩石力学与工程学报,2009,28(增刊2):3769-3775.GUO Qing-lin,WANG Xun-dong,XUE Ping,et al.Research on spatial distribution and relations of salinity and moisture content inside rock mass of low-layer caves in Dunhuang Mogao Grottoes[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(Supp.2):3769-3775.
[12]邴慧,武俊杰,邓津.黄土状盐渍土洗盐前后物理力学性质的变化[J].冰川冻土,2011,33(4):796-800.BING Hui,WU Jun-jie,DENG Jin.Variations of physical and mechanical properties of saline loess before and after desalting[J].Journal of Glaciology and Geocryology,2011,33(4):796-800.
[13]刘刚,薛平,侯文芳.莫高窟85窟微气象环境的监测研究[J].敦煌研究,2000(1):36-41.LIU Gang,XUE Ping,HOU Wen-fang,et al.Monitoring micro-meteorological enviroment of Cave 85 of Mogao Grottoes[J].Dunhuang Research,2000(1):36-41.
[14]赵林毅,李燕飞,于宗仁,等.丝绸之路石窟壁画地仗制作材料及工艺分析[J].敦煌研究,2005,(4):75-82.ZHAO Lin-yi,LI Yan-fei,YU Zong-ren,et al.The technique and materials about making the wall paintings of the Mogao Grottoes on the silk road[J].Dunhuang Research,2005,(4):75-82.
[15]HAYNES W M.CRC Handbook of chemistry and physics[M].91st edition.Florida:CRC Press Inc.,2010.
[16]HALL C.Water sorptivity of mortars and concretes[J].Magazine of Concrete Research,1989,41(147):51-61
[17]FREDLUND D G,RALLARDJO H.Soil mechanics for unsaturated soils[M].New York:John Wiley&Sons,1993.
[18]高世桥,刘海鹏.毛细力学[M].北京:科学出版社,2010.GAO Shi-qiao,LIU Hai-peng.Capillary mechanics[M].Beijing:Science Press,2010.
[19]刘光启,马连湘,刘杰.化学化工物性手册——无机卷[M].北京:化学化工出版社,2002.LIU Guang-qi,MA Lian-xiang,LIU Jie.Handbook of chemistry and chemical properties[M].Beijing:Chemical Industry Press,2002.
[20]玉亚.土壤接触角及土壤表面能量特征的研究[D].西安:西安建筑科技大学,2007.YU Ya.A study on contact angle and soil surface free energy properties[D].Xi’an:Xi’an University of Architecture and Technology,2007.
[21]王全九,邵明安,郑纪勇.土壤中水分运动与溶质迁移[M].北京:中国水利水电出版社,2007.WANG Quan-jiu,SHAO Ming-an,ZHENG Ji-yong,et al.Water movement and solute transport in soils[M].Beijing:China Water&Power Press,2007.
[22]NIELSEN D R,BIGGAR J W.Water flow and solute transport processes in the unsaturated zone[J].Water Resources Research,1986,22(9):89S-108S.
[23]RIJNIERS L A,PEL L,HUININK H P,et al.Salt crystallization as damage mechanism in porous building materials——A nuclear magnetic resonance study[J].Magnetic Resonance Imaging,2005,23(2):273-276.
[24]CHAROLA A E.Salts in the deterioration of porous materials:An overview[J].Journal of the American Institute for Conservation,2000,39(3):327-343.
[25]HANS-JüRGEN B,KARLHEINZ G,MICHAEL K.Physics and chemistry of interfaces[M].Darmstadt:betz-druck Gmbh,2006.
[26]MVBB G R,KOLAY P K,SINGH D N.Thermal characteristics of a class fly ash[J].Cement and Concrete Research,1998,28(6):841-846.
[27]邓友生,何平,周成林.含盐土导热系数的试验研究[J].冰川冻土,2004,26(3):319-323.DENG You-sheng,HE Ping,ZHOU Cheng-lin.An experimental research on the thermal conductivity coefficient of saline soil[J].Journal of Glaciology and Geocryology,2004,26(3):319-323.
[28]SCHERER G W.Stress from crystallization of salt[J].Cement and Concrete Research,2004,34(9):1613-1624.