【作者】 陈琼；

【导师】 项伟；

【作者基本信息】 中国地质大学 ， 岩土工程， 2013， 博士

【摘要】 黏土中的结合水是黏土矿物颗粒如蒙脱石、高岭石或伊利石等与水蒸气或水溶液在一定环境下相互作用的产物,一直是土质学、土力学、工程地质学、环境地质学、土壤学、胶体化学和矿物学等学科重点研究的问题之一。黏土结合水的性状、存在形式、扩散性、流动性与渗透性是控制黏土液塑限、水化膨胀、分散、收缩、比表面积、孔隙结构、微表面结构、土-水特征曲线、强度和变形等物理力学性质,PH值、电导率、吸附热、Zeta电位、阳离子的交换容量和可交换阳离子等电化学性质的重要因素。结合水的存在使其对黏土所表现出来的物理-化学-力学性质具有强烈影响,同时还是引发黏土一系列工程地质问题的重要因子。随着大家对黏土中结合水研究的深入,已经得出结合水在黏土中所起的作用非常大,但通过对已发表的论文进行研究发现,以往的研究缺乏对黏土吸附结合水统一量化模型和理论,因此,亟需开展黏土在水蒸气中、在土-水界面吸附-脱附结合水动力学的模型研究。本文的选题正是基于这一点,尝试建立一个能解释在不同物理界面条件下,黏土吸附结合水的曲线模型和机理,这是解决相关理论的试验基础和关键技术。本论文以Na-蒙脱土、纯高岭土、黄土坡滑坡滑带土、膨胀土和武汉红色黏土等5种黏土为研究对象,在获得各种黏土的基本物理性质、力学性质、矿物成分、全量化学成分和电化学性质的基础上,主要采用中国地质大学(武汉)工程学院试验中心改进的美国Quanta Chrome公司AutoSorb iQ全自动吸附仪和Poremaster33压汞仪、改进能测量结合水体积的美国Soil Moisture Equipment公司制造的200kPa、500kPa压力板仪,英国GDS公司制造的非饱和土直剪仪(底部陶土板的进气值是1000kPa)等设备,研究各种黏土吸附结合水的等温吸附性质和吸附动力学特性,揭示黏土自水蒸气中、自土-水界面吸附结合水的机理,创建黏土吸附结合水控制理论与方法,为合理控制和利用黏土水化、分散、膨胀、渗透性质,调控黏土物理力学性质、化学性质以满足工程应用提供重要的理论支撑和试验数据,具有十分重要的科学意义。论文主要研究内容如下：(1)选取Na-蒙脱土、纯高岭土、湖北省巴东县黄土坡滑坡滑带土、河南膨胀土和武汉红色黏土等5种代表性黏土,通过对其矿物成分的分析,发现这5种黏土都含有膨胀性黏土矿物蒙脱石和高岭石,由于黏土矿物表面在干燥状态下具有一定的表面能和大量的孔隙,所以无论是在水蒸气中、还是在土一水界面,只要有水分子的存在,它们都会吸附不同类型的结合水。以Na-蒙脱土为例,其与不同类型结合水的“结合能,,不同,因此在对其进行热分析时,不同“结合能”影响范围内的结合水将在不同温度区间被脱去,从而在差示扫描量热曲线上相应温度处产生一定的吸热谷,分别是106.6℃和150.5℃,分别表示弱结合水与强结合水的界限。从DSC吸热谷的形态和面积来看,弱结合水处吸热谷的面积、峰宽均比强结合水处的大,表明弱结合水的“结合能”较弱,较强结合水的“结合能,,控制范围更宽。研究了蒙脱土在不同初始含水率状态下吸附强结合水和弱结合水的结合能。从不同初始含水率的蒙脱土热重和差示扫描量热曲线得出,初始含水率不影响蒙脱土的强结合水和弱结合水的位置,但是不同初始含水率的热失重截然不同,初始含水率越大,其热失重的质量百分数越高；从差示扫描量热曲线来看,不同初始含水率亦不改变其吸热谷的位置,依旧是在106.6℃和150.5℃有2个吸热谷。(2)在相对压力为0.05～0.95范围,经105℃烘干蒙脱土单位质量吸附结合水的量比经150’C烘干蒙脱土吸附结合水的量多。当加热温度小于105℃时,蒙脱土吸附结合水的量随着加热处理温度的升高而增大,当加热温度大于105℃时,蒙脱土吸附结合水的量随着加热处理温度的升高而减小。这与经验的烘干吸水规律相反,一般认为当蒙脱土失去强结合水时,会分别吸附强结合水和弱结合水,所以其吸附结合水的量应该比失去弱结合水的蒙脱土吸附更多水分子,但试验结果恰恰相反。研究结果表明,当水合阳离子中的水和晶层表面的弱结合水脱去后,蒙脱石晶胞内不同电性离子之间的静电作用势、交换性阳离子与晶层间的静电作用势、层间水分子与晶层的氢键作用势等增强了,在综合作用势的作用下,蒙脱石晶体重新达到另一个平衡,使得其整体表现出对外界水分子吸附能减弱。(3)在相对压力小于0.3的范围内,105℃烘干蒙脱土吸附结合水的“结合能,,比150℃烘干蒙脱土吸附结合水的“结合能”大。初始的线性吸附阶段,105℃烘干蒙脱土吸附点拟合曲线的斜率明显大于150℃烘干蒙脱土的。说明在该区间,105℃烘干蒙脱土吸附结合水的能量和吸附结合水的量均大于150℃烘干蒙脱土的。从2种烘干状态下的吸附量差值来看,在相对压力小于0.6的区间内,105℃烘干蒙脱土吸附结合水的单点吸附量和累积吸附量均大于150℃烘干蒙脱土的,在相对压力为0.6时,2种烘干状态下的吸附结合水的量几乎相同。当相对压力大于0.6后,虽然105℃烘干蒙脱土吸附结合水的单点吸附量和累积吸附量亦均大于150℃烘干蒙脱土的,但是其“结合能”明显低于相对压力小于0.6时的。说明蒙脱土脱水后,只要相对压力适当,自由水分子足够多,在静止状态下,可以找到一个2种不同烘干状态后吸附相同结合水的点,称之为“等结合能”吸附点。尽管2种烘干状态下Na-蒙脱土的吸附能量不同,单点的吸附量有差值,但是可以看出,在接近饱和状态时(相对压力为0.95),蒙脱土吸附结合水的量是其自身质量的近350倍。(4)纯高岭土10次循环吸附-脱附试验结果表明,经105℃烘干后的纯高岭土,在20℃水浴环境下,在相对压力小于0.52时,其表面吸附能相对较大,单位质量纯高岭土第1次与第2次吸附结合水的量最大差值可达7.4184cc/g。而其他9次吸附试验结果表明,其吸附量的差值平均为2.36cc/g。可以得出：纯高岭土经105℃加热后,在相对压力为0.048305时,第1次吸附结合水的量最大仅为3.3233cc/g,此时水分子没有完全铺满高岭土表面,第2次吸附以后,吸附结合水的量最大可达11.165cc/g,此时结合水已经完全铺满高岭土表面。高岭土最大脱附结合水量与最大吸附结合水量差值为10.7417cc/g,为高岭土在20—105℃区间内吸附能所吸附的结合水量。且由于高岭土中氢键、范德华力的存在,使得结合水的吸附势能非常高,这部分结合水在20℃时,不会由于干湿循环而脱去。(5)滑带土10次循环吸附—脱附试验结果表明,经105℃烘干后的滑带土,在20℃水浴环境中,在相对压力小于0.76时,其表面吸附能相对较大,单位质量滑带土第1次与第2次吸附结合水的量最大差值可达3.8915cc/g。而其他9次吸附试验结果表明,其吸附量的差值平均为1.03cc/g。可以得出：滑带土经105℃加热后,在相对压力为0.047278时,第1次吸附结合水的量最大仅为0.25cc/g,此时水分子仅占据吸附能较大的滑带土表面,第2次吸附以后,吸附结合水的量最大可达6.7762cc/g,此时结合水已经完全占据滑带土表面。滑带土最大脱附结合水量与最大吸附结合水量差值为6.703cc/g,为滑带土在20—105℃区间内吸附能所吸附的结合水量。在相对压力大于0.80后,由于结合水已经完全形成,此时多次吸附—脱附结果相差不大,说明吸附—脱险的水主要是自由水。(6)膨胀土9次循环吸附—脱附试验结果表明,经105℃烘干后的膨胀土,在20℃水浴环境下,在相对压力小于0.3时,其表面吸附能相对较大,单位质量膨胀土第1次与第2次吸附结合水的量最大差值可达171.6823cc/g。而其他8次吸附试验结果表明,其吸附量的差值平均为30cc/g。可以得出：膨胀土经105℃加热后,在相对压力为0.052882时,第1次吸附结合水的量最大仅为262.8088cc/g,此时水分子没有完全铺满膨胀土表面,第2次吸附以后,吸附结合水的量最大可达497.7739cc/g,此时结合水已经完全铺满膨胀土表面。膨胀土最大脱附结合水量与最大吸附结合水量差值为434.4911cc/g,为膨胀土在20—105℃区间内吸附能所吸附的结合水量。(7)红色黏土9次循环吸附—脱附试验结果表明,经105℃烘干后的红色黏土,在20℃水浴环境下,在相对压力小于0.68时,其表面吸附能相对较大,单位质量红色黏土第1次与第2次吸附结合水的量最大差值可达6.3285cc/g。而其他8次吸附试验结果表明,其吸附量的差值平均为0.828cc/g。可以得出：红色黏土经105℃加热后,在相对压力为0.047278时,第1次吸附结合水的量最大仅为12.2122cc/g,此时水分子没有完全铺满红色黏土表面,第2次吸附以后,吸附结合水的量最大可达20.0101cc/g,此时结合水已经完全铺满红色黏土表面。红色黏土最大脱附结合水量与最大吸附结合水量差值为23.0784cc/g,为红色黏土在20—105℃区间内吸附能所吸附的结合水量。(8)通过对不同黏土的吸附动力学曲线进行分析,可以得出,不同的土在不同的相对压力下吸附结合水的动力学曲线截然不同,但都有—个共同的规律：随着相对压力的升高,在黏土表面吸附结合水的动力学曲线中,5秒内的结合能系数K5s,均是减小的趋势。随着相对压力的增大,吸附结合水平衡所需要的时间都有先增大后减小的规律。这是因为在黏土颗粒表面形成单层水分子之前,黏土的表面能非常大,所以其吸附结合水的平衡时间逐渐增大;当黏土颗粒表面形成单层或多层水分子之后,黏土表面的吸附能逐渐减小,毛细吸力逐渐占据主要位置,所以其吸附结合水的平衡时间逐渐减小。(9)根据水蒸气吸附—脱附数据计算出黏土的比表面积比氮气吸附的大,这是因为水分子具有极性,在氢键的作用下,更容易与黏土颗粒和表面阳离子结合。根据水蒸气吸附—脱附数据计算出黏土的表面分形维数大于氮气吸附数据计算得出的,说明不是所有水分子能进入的孔隙氮气分子都可以进入,而且极性水分子在氢键作用下,会进入更粗糙的黏土矿物表面。与冻干样相比,黏土烘干样吸附结合水的能力变小,因为黏土矿物和表面的水合阳离子失水后,在静电作用和氢键作用下,黏土颗粒靠得更近,化学键重新分配,孔隙变得更小,使水分子难以进入,最终导致黏土单位吸附结合水量减少。(10)综合水蒸气吸附法和恒速压汞法可以测量孔径的范围更大,揭示的孔径范围更广。黏土烘干样中墨水瓶形和狭缝形结构的孔隙容易使水分子与黏土矿物形成氢键,阻止结合水的进一步吸附,导致测量的比表面积和孔隙体积比冻干样的少,且其表面分形维数比冻干样的小,说明在引力作用下,孔隙表面粗糙度减小。水蒸气吸附试验适宜评价的孔径范围是微孔区间0.825～17.925nm；恒速压汞试验适宜评价的孔隙范围是中孔和大孔区间。在微孔和中孔区间,冻干黏土的孔隙直径和孔隙体积均大于烘干样。黏土烘干样由于失水体积收缩,在分子键和氢键作用下,颗粒之间连接得更加紧密,团粒直径比冻干样的大。更多还原

【Abstract】 The bound water in clays is the result of interaction between clay minerals such as montmorillonite, kaolinite, illite etc. and water vapor or water liquid, which has been the key study focus no matter in soil science, soil mechanics, engineering geology, environmental geology, colloid chemistry or in mineralogy. The physical-mechanic and electrochemical properties of clays largely depend on the characteristics of bound water specifically for categories, diffusivity, fluidity and permeability. In other words, it is evident that properties of liquid and plasticity, hydration swelling, dispersion, shrinkage, specific surface area, pore structure, micro-structure, soil water characteristic curve, strength, deformation, PH, conductivity, adsorption heat, Zeta potential, categories of exchangeable cations and cation exchange capacity are controlled by the properties of bound water. Due to having a great impact on the physical-chemical-mechanic properties of clays, the bound water is the key factor to lead to many problems of engineering geology involved in clays. There are large number of researches on bound water of clay, however, the study on universal model and theory of water absorbed are rather limited. Thus, it is quite crucial to study kinetic model of adsorption-desorption bound water at different conditions such as clay in water vapor, in the interface between terracotta panels and water liquid and in electrolyte solution. The purpose of this paper is to try to establish the model and theory of water adsorption-desorption on clay that are able to interpret and predict the adsorptive behaviors of water absorbed by clay at various conditions.The experimental materials in this investigation consists of five categories of clays. Montmorillonite, pure kaolinite, sliding zone soil obtained from Huang Tupo Landislide, bentonite acquires in Henan and red clay in Wuhan, respectively. The basic physical-mechanic indexes, mineral component, microchemistry component and electrochemical parameters are acquired using a variety of test instruments. Then to reveal the adsorptive mechanism of clay at water vapor, the interface between terracotta panels and water liquid and in electrolyte solution, the isothermal adsorption and desorption and kinetic experiments are accomplished using AutoSorb iQ sorbing instrument, mercury injection apparatus (Poremaster33, made in America), soil moisture equipment and unsaturated soil direct shear apparatus (GDS, made in British). The major studies are shown as follows.(1) The chemical analysis test demonstrates that all of five kinds of clay, Montmorillonite, pure kaolin, red clay in WuHan, sliding zone soil of Yellow Slope and bentonite in Henan, contain swelling clay minerals such as montmorillonite and kaolinite. Due to the surface of clay minerals having a certain surface energy and a lot of pore in the dry state, they can absorb different types of bound water whether it is in the water or in the interface between soil and water as long as there is water molecular. For example different categories of bound water in Montmorillonite correspond to different hydration interaction. And the analysis of Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC) could reflect the relationship between the temperature and hydration interaction. Therefore, various categories of bound water would be desorbed at corresponding temperature ranges such as the two endothermic peaks in curve of DSC at106.6℃and150.5℃, respectively. Actually, these temperature points are the borders of bound water and power bound water. The shapes and area of endothermic peaks indicate that the peak area and peak width of bound water is larger than ones of power bound wate, which is considered that the affecting range of the hydration interaction of bound water is less than one of power bound water. Hydration interaction to adsorbing different kinds of bound water was studied using a variety of initial water content of montmorillonite. According to the curves of TG and DSC, initial moisture content does not have an impact on locations of bound water and power bound water. But the thermal weightlessness of different initial moisture content is quite different and higher initial moisture content can lead to higher mass percentage of thermal weightlessness. From the point of DSC, different initial moisture content does not change its position of endothermic peaks which is still at106.6℃and150.5℃.(2) At the0.05～0.95relative pressure, the hydration interaction of the unit of montmorillonite mass dried at105℃is more than one dried at150℃. When the heated temperature is less than105℃, the amount of adsorption bound water increases with the rise of heat treatment temperature. However, when heating temperature is greater than105℃, the amount of adsorption bound water of montmorillonite decreases with raising heat treatment temperature. But this is opposite with the experience of drying water absorption regularity and it is generally believed when montmorillonite lost strong bound water, it will respectively absorb strong bound water and weakly bound water as a result that the amount of adsorption bound water of montmorillonite is supposed to be higher than the montmorillonite that lost weakly bound water, but the test result is just the opposite. The research results show that when weakly bound water of water and crystal layer surface in the hydrated cation desorbed, the electrostatic potential among different electrical ion, the electrostatic potential of exchangeable cation and crystal layer, hydrogen bonding potential of interlayer water molecules and crystal layer in montmorillonite crystal intracellular are enhanced and under the effect of combined action potential, montmorillonite crystal will reach a new balance, making the entirety show decrease of water molecules adsorption energy to the outside.(3) When relative pressure is less than0.3, the hydration interaction of montmorillonite dries at105℃is more than that dried at150℃. In the stage of initial linear adsorption, the slope of the fitted curve of montmorillonite adsorption dried at105℃is significantly greater than one dried at150℃. In this interval, the energy and amount of bound water adsorbed of montmorillonite dried at105℃are greater than one dried at150℃. From the difference of adsorption between the two kinds of drying conditions, when the relative pressure is less than0.6, the single point and cumulative adsorption of drying montmorillonite of105℃are greater than150℃, and at a relative pressure of0.6, amount of bound water adsorbed of two drying condition is almost the same. After the relative pressure is greater than0.6, while the single point and cumulative adsorption of drying montmorillonite of105℃are not less than150℃, its hydration interaction is significantly lower than the relative pressure of smaller than0.6. This indicates that as long as the proper relative pressure and enough free water molecules, in static state, the point of the same water adsorbed under two different drying states can be found in the montmorillonite after dehydration, called "equal binding energy" adsorption point. Although adsorption energy of Na-montmorillonite between the two kinds of drying conditions is different, and the single point of the adsorption has difference, it can be seen that when nearly saturated state (0.95), the amount of bound water adsorbed of montmorillonite is nearly350times its quality.(4) Test results of10adsorption-desorption cycles of pure kaolin show that when the relative pressure is less than0.52, the surface adsorption of pure kaolin after dried at105癈is relatively large at water bath environment dried at20℃, and the maximum difference between1st and2nd the amount of water adsorbed of per unit mass pure kaolin can be up to7.4184cc/g. The other nine adsorption test results show that difference of adsorption is at an average of2.36cc/g. It is concluded that pure kaolin after heating of105℃, when the relative pressure is0.048305. the first largest adsorption of bound water of pure kaolin after heating of105℃is just3.3233cc/g, water molecules are not fully covered with surface of kaolin at this time, after the second adsorption, the adsorption of bound water can reach11.165cc/g, while bound water is fully covered with surface of kaolin. The difference between the bound water adsorbed of the maximum desorption and maximum adsorption is10.7417cc/g for kaolin, as bound water adsorbed by binding energy in20-105℃. And due to hydrogen bond and van der Waals of kaolin, adsorption potential of bound water is very high, and this part of bound water won’t take off because of dry-wet circulation at20℃.(5) The adsorption-desorption cycles experiments results indicate that when the relative pressure is below0.76, the hydration interaction of sliding zone soil is quite evident and large. The maximum adsorptive difference occurs to the first and second cycles and is6.7762cc/g, whereas the sorption variances of the other cycles are relatively small and their mean difference is1.03cc/g. After samples are heated at105℃for24hours, the largest amount of water absorbed in the first cycle is only0.25cc/g at0.047278relative pressure, which is designed as the process that only the surface with lager sorption ability appears to water adsorption. The amount of water absorbed in the second cycle, however, is up to6.7762cc/g, which is considered as stage that the surface of sliding zone clay has been absolutely occupied by water molecule. Besides, the difference between the largest amount of water desorbed and the largest amount of water adsorbed is6.703cc/g, which is designed as the bound water adsorbed by adsorption capacity located in20-105℃. When the relative pressure is over0.80, the variance between amount of adsorption and desorption is quite little, which suggests that owing to the bound water film having completely formed, the majority of water adsorbed or desorbed is water molecular indirectly link to surface.(6) Experiments of9adsorption-desorption cycles of bentonite show that expansive soil after dried at105℃has relatively bigger surface adsorption energy and the amount of adsorbed bound water’s maximum difference in the first and second adsorption of unit mass of expansive soil can reach171.6823cc/g at the20℃water bath environment when the relative pressure is smaller than0.3. While the other eight adsorption experiments results show that the average of adsorption amount’s difference is30cc/g. It can be concluded that after dried at105℃, the first largest adsorption amount of bound water is just262.8088cc/g and after the second adsorption, the largest adsorption amount of bound water can reach497.7739cc/g when the relative pressure is0.052882and at this moment, bound water is fully covered with expansive soil’s surface. The difference between expansive soil’s maximum desorption of bound water and maximum adsorption of bound water is434.4911cc/g as the expansive soil’s amount of bound water which is adsorbed by adsorption energy in the range of20-105℃.(7) Experiments of9adsorption-desorption cycles of red clays show that red clay after dried at105℃has more surface adsorption energy and the maximum difference of amount of bound water in the first and second adsorptions can reach6.3285cc/g when the relative pressure is smaller than0.68. However, the other eight adsorption experimental results show that the average difference of adsorption amount is0.828cc/g. When the relative pressure is0.047278, largest adsorption amount of bound water in the first adsorption is only12.2122cc/g, whereas the largest adsorption amount of bound water in second adsorption can reach20.0101cc/g. The above phenomena results from whether the surface of red clay is completely covered by bound water. additionally, the difference between the largest amount of water desorbed and the largest amount of water adsorbed is23.0784cc/g, which is designed as the bound water adsorbed by adsorption capacity located in20-105℃.(8) The experiments of adsorption kinetics show that the curves of adsorption kinetics are rather different, which is dependent on the categories of clay and conditions of water relative pressure. But it is quite consistent that the all of coefficients of hydration interaction under five seconds decrease and the equilibrium time to adsorbing bound water grows up then decrease with increasing the relative pressure. Above phenomena first result from that the hydration interaction is greatly large before the monomolecular water layer occurs in particle of clays. Once the monomolecular water layer or multi-molecular is accomplished, however, the hydration interaction gradually lowers and capillary interaction in gradual plays the controlling role. Therefore, the equilibrium time to adsorbing bound water gradually decreases.(9) The specific surface area calculated upon BET theory indicates that the specific surface area using water vapor desorption isotherm is greatly larger than one using nitrogen desorption isotherm, which results from that due to water molecular being polar and having hydrogen bound, it is more easily to be absorbed by cations of surface. Additionally, the phenomenon that surface fractal dimension calculated from water vapor adsorption-desorption isotherms is larger than one obtained from nitrogen adsorption-desorption isotherms implies that other than pore that nitrogen molecular could come in, water molecular is able to go to the pore located in the rougher surface. Comparison to freeze-dried samples, the hydration interaction of heated-dried samples is less, which is designed that the heating treatment results in the water molecular directly link to surface and exchangeable cation desorbed. Moreover, under the synactic interaction of electrostatic interactions and hydrogen bonds, the particle of clay becomes closer and chemical bonds redistribute, which results in that pore becomes smaller. These changes lead that it is more difficulty for water molecular to come into the pore and finally that the amount of water absorbed by per gram clay decreases.(10) Integrated water vapor adsorption method and constant speed mercury injection method are able to use to measure large size of aperture and reveal wider scope of the aperture. The ink bottle shape pore and slit-shaped structure pore in the dry clay sample can make water molecules and clay minerals form hydrogen bond easily and prevent further adsorption of bound water, which has contributed to less specific surface area and pore volume of measurement than freeze-dried sample and smaller surface fractal dimension than freeze-dried sample, showing that pore surface roughness decrease under the action of attraction. The suitable aperture range which is evaluated by the water vapor adsorption experiment is micro-porous range which is from0.825to17.925nm. But the suitable aperture ranges which is evaluated by constant speed mercury injection experiment are mesoporous and macroporous range. In the micro-porous and mesoporous range, the pore diameter and pore volume of freeze-dried clay are both bigger than drying clay’s. Because of the volume dehydration shrinkage of drying clay sample, the connection among particles become closer and the pellets diameter is bigger than freeze-dried sample’s under the effect of molecular bond and hydrogen bond.更多还原