基于大尺度仿真模拟试验的夯土遗址Na2SO4-NaCl盐风化机理研究

Salt weathering is the critical factor causing damages and corrosion of rammed earthen sites. Rammed earthen sites with Na2SO4-NaCl salt mixtures as the object of this research, theoretical phase behavior model of system formed by Na+-SO42--Cl－-H2O is intended to be established and the value of key parameters such as phase-transition temperatures, humidity and salt proportion to be determined. In this way, crystallization and deliquescence characteristics of salt mixtures in soil will be thereby explored. Based on these analysis, simulation experiments using large-scale rammed earth models are conducted to reveal the influences of internal factors (soil structures) and external factors (environmental factors) on salt weathering behavior of rammed earth with salt mixtures inside. Monitoring and measurements are carried out at both macro and micro levels. On macro aspects, regulations of salt migration and accumulation, changes of overall features of rammed earth, strength degradation of soil mass and occurrence of diseases and damages will be monitored. On micro aspects, sizes and distributions of pores in rammed earth, changes of bonds between soil particles and mineral composition will be analyzed, respectively. The relationship between all impact factors mentioned above and salt weathering behavior is therefore quantitatively researched to uncover development mechanism of damages induced by salt mixtures in soil. Research findings will lay the foundation for evaluation system and integral control of diseases by salt weathering of rammed earthen sites.

盐风化是导致夯土遗址多种病害产生和发育的关键因素。本项目拟以含Na2SO4-NaCl混合盐的夯土遗址为研究对象，建立Na+-SO42--Cl－-H2O系统的理论相态模型，确定Na2SO4-NaCl混合盐相态转变温度、湿度及盐分配比等关键参数，进而探明Na2SO4-NaCl混合盐在土中的结晶-溶解特性。通过大尺度仿真模拟试验，研究土的内部因素（土的结构）及外部因素（环境因素）对含Na2SO4-NaCl混合盐的夯土盐风化的影响。从宏观层面，跟踪监测土中盐分迁移、富集规律、夯土整体形貌的变化、土体强度衰变以及病害的产生、发育等；从微观层面，分析土的孔隙大小、孔隙分布、土颗粒间胶结状况以及矿物成分的变化。通过宏观、微观两个层面，定量化评估各影响因子与土体盐风化之间的相互关系，揭示夯土遗址在混合盐风化诱导下的病害形成与发展机制，为病害评估体系的建立及盐风化病害综合防治提供基础。

土遗址是我国重要的文化遗产之一，是中华文明形成、发展及演化的重要实物资料，保护好、传承好、利用好这些文化遗产，对于继承和发扬中华民族优秀传统文化具有重大意义。其中，土遗址盐风化机理的深入研究是防风化治理的重要理论基础。研究项目首先开展了Na2SO4-NaCl-H2O体系结晶-溶解特性研究，建立了Na+-SO42--Cl--H2O系统的理论相态模型，从物理化学的角度分析确定Na2SO4-NaCl 混合盐的共饱和点、相态转变温度、湿度及浓度比等关键参数。通过纯溶液称量瓶蒸发实验以及重塑土样模拟试验，开展Na2SO4-NaCl-H2O体系在不同温湿度条件下的结晶路径、相态转变等结晶特性研究。其次通过电子扫描显微镜（SEM）、离子色谱、三维扫描、声波仪、表面硬度仪等分析测试手段，研究不同土体结构及环境条件及下含Na2SO4-NaCl混合盐土遗址的劣化特征，包括土体劣化模式、质量和体积损失率和强度变化等，以及土体中盐分的迁移结晶规律。并且，以土体劣化程度为指标，采用多元线性回归的方法探究各影响因素与遗址土盐风化之间的定量关系。最后利用夯筑法制作体积为1m（长）*1.5m（宽）*2m（高）的大型模拟实验墙体，基于大尺度模拟实验对土遗址Na2SO4-NaCl盐风化机理进行探索性研究，得到了大尺度夯土遗址盐风化过程中的盐分富集、劣化破坏模式。研究结果对于遗址土盐风化的内部及外部影响因素作用机制进行了深入探讨，对土遗址的病害防治及预防性保护具有重要的理论意义和实际指导作用。