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《Dunhuang Research》 2013-01
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A Preliminary Study of the Freeze-thaw Cycle on the Structure of Earthen Sites with Different Salts

CHEN Yu1 WANG Xudong1,2,3 YANG Shanlong2,3 GUO Qinglin2,3 LIN Bo1 LI Fengjie1(1.School of Civil Engineering and Mechanics of Lanzhou University,Lanzhou,Gansu 730000;2.National Research Center for Conservation of Ancient Wall Paintings,Dunhuang,Gansu 736200;3.Conservation Institute,Dunhuang Academy,Dunhuang,Gansu 736200)  
Owing to environmental factors,serious salt damages have appeared in the earthen sites in arid region of northwest China.The wet-dry and freeze-thaw cycles cause repeated salt migration in the soil and thus change the soil porosity.Some cubic samples of 5 cm 3 are made of local washed soil of Dunhuang and mixed with a compound salt containing sodium chloride and sodium sulfate in various proportions,and then exposed to a freeze-thaw action.In this way,the changes in the soil porosity after each cycle can be observed with a microscope.During early indoor weathering experiments,the salt expansion effect of the test samples of optimum moisture content containing Na 2 SO 4 is far greater than that of the samples containing NaCl.According to the weathered experiments results,various kinds of test samples containing different salts are redesigned for freeze-thaw cycle tests.The results show that the more the freeze-thaw cycles increase,the less porosity exists between soil particles and the pores are gradually filled with salts.This is more obvious as the salt content increases.Compared with NaCl,Na 2 SO 4 is more sensitive to moisture and will crystallizes rapidly when contacting water and damages the test samples.The reaction of the test samples containing different proportions of the combination of NaCl and Na 2 SO 4 can be considered as the result of the interaction of the two single salts.Studying the microstructure of the test samples with a microscope can help capture the mecha nism of salt deterioration on earthen sites,and then provide a scientific basis for the consolidation and protection of earthen sites.
【Fund】: 敦煌研究院院级课题“干旱环境土遗址脱盐室内试验初步研究”([2010]11);; 甘肃省科技支撑计划“敦煌莫高窟壁画病害水盐来源及防治对策研究”(1011FKCF107)
【CateGory Index】: P642.1
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