碳纳米管改性黏土力学性能及微观机制研究

Experimental Study on Mechanical Properties and Micro-mechanism of Clay Modified by Carbon Nanotubes

研究多壁碳纳米管(MWCNTs)改性黏土力学性能,旨在将其应用于垃圾填埋场衬垫材料的设计和施工中。通过三轴压缩试验和扫描电子显微镜(SEM)试验,分析了不同MWCNTs掺量(质量分数,下同)对黏土抗剪强度的影响规律,并从微观结构演化规律方面揭示了宏观力学特性变化机理。三轴试验结果表明,抗剪强度随MWCNTs掺量增加,表现为先增加后减小,0.5%MWCNTs掺量抗剪强度值最大,且掺加多壁碳纳米管试样的抗剪强度均大于未掺入试样;随MWCNTs掺量增加,黏聚力的发展规律与抗剪强度一致,最大值出现在0.5%~1.0%;内摩擦角则随MWCNTs掺量增加表现为先减小后增大,在1%左右MWCNTs掺量处最小。掺入0.5%~1.0%的MWCNTs可以有效提高黏土的抗剪强度。掺加MWCNTs改变土体微观结构是引起其宏观力学特性变化的根本原因。分析SEM结果表明,无MWCNTs掺量的试样中黏土颗粒间接触较为紧密,大、小孔隙分布较为均匀;掺入MWCNTs之后,土样孔隙的数量和尺寸均发生了明显改变。掺量较低时(0.5%),MWCNTs附着在土颗粒表面,填充孔隙使得孔隙尺寸减小,增加了土样的密实性,从而使得抗剪强度增大;随着MWCNTs掺量增加(1%和2%)可以观察到试样孔隙数量增多,但均少于无MWCNTs掺量试样中的孔隙数量,这种现象归因于MWCNTs自身的润滑作用减弱了其对黏土颗粒的吸附胶结作用,导致抗剪强度减小。

Studying the influence of multi-walled carbon nanotubes(MWCNTs)contents on mechanical properties of modified saturated clay is of great significance for its design and application in refuse landfill clay liner materials.Triaxial compression tests and scanning electron microscope(SEM)tests were performed to analyze the influence of different MWCNTs contents on the shear strength and the mechanism of mechanical properties was revealed from the microstructure evolution.The triaxial tests results showed that the shear strength increased first and then decreased with the increasing MWCNTs content,and the maximum value was detected at 0.5%MWCNTs content.The shear strength of samples doped with MWCNTs was greater than that without content.The cohesion strength showed similar change tend with the shear strength and the maximum value existed between 0.5%and 1.0%.The internal friction angle first decreased and then increased with the increasing MWCNTs content,and the minimum value appeared at 1.0%content.The results indicated that the shear strength of clay could be significantly improved by mixing MWCNTs with 0.5%-1.0%content.The MWCNTs altered the microstructure of the clay,which was the main cause of the change in the soil macroscopic mechanical properties.SEM results indicated that the contact between clay particles was relatively close and the large and small pores showed a uniform distribution in the specimen without MWCNTs content.The number and size of pores in the soil sample changed significantly after adding MWCNTs.It increased the compactness of the specimen with lower content,in which the threshold was determined to be 0.5%content,leading to the increase in shear strength.It could be observed that the number of pores increased but was less than the specimen without content with the increasing MWCNTs contents(1%and 2%).It could be attributed to the reason that the adsorption and cementation of MWCNTs on soil particles were weakened due to lubricating effect,resulting in a decrease in shear strength.