复合改性水玻璃加固黄土微观特征研究

进行压汞试验和SEM-EDS试验研究复合改性前后水玻璃加固黄土，分析其孔隙分布特征、颗粒和孔隙形态以及胶结物形态和化学元素含量，探讨宏观力学特性与微观特征的联系。压汞测试结果表明，改性前后加固黄土具有相近的孔隙分布特征，入口孔径主要分布在0.06～8 ?m之间，大、中、小和微孔隙分界值分别为8、2、0.06 ?m，加固时生成的凝胶填充作用不显著。SEM-EDS测试结果表明，改性后黄土仍保持其粒状、架空、接触-胶结结构不变，但加入硅酸钾材料后黄土颗粒表面变得粗糙并吸附有絮状物，EDS数据显示K元素含量随着硅酸钾掺入量的增加而增大，且试样无侧限强度与K元素百分含量正相关。研究还表明，土的颗粒联结强度和结构形态特征是导致黄土宏观力学性质差异的本质原因，在复合改性水玻璃加固黄土时在保持黄土架空孔隙基本不变的前提下，生成的含K凝胶在改变颗粒表面形态的同时强化了骨架颗粒之间的连接强度，从而改善了土体的强度。

Microstructure of loess reinforced by compositely modified sodium silicate

Silicification is one of the chemical methods of collapsible loess treatments. Sodium silicate is modified by potassium silicate for better reinforced effect. The mercury intrusion porosimetry (MIP), scanning electron microscope and energy dispersive spectrometer tests (SEM-EDS) are performed on the loess specimens reinforced by compound modified sodium silicate. The microscopic characteristics, such as the entrance pore size distributions, particles' morphology and chemical composition, are carried out. Meanwhile, the relationship between microstructure, chemical composition and macroscopic mechanical behavior is also discussed. Based on the results of MIP, similar entrance pore size distributions, the dual-porosity structure, were found in both modified and unmodified reinforced loess specimens. And the entrance pore size distribution ranges from 0.06 to 8 ?m. According to the decreasing size, the pores can be labeled as large, medium, small and micro-pore, among which the three critical values are 8, 2 and 0.06 ?m, respectively. Moreover, gel-filled effect can be observed if reinforced effect is not significant. The results of SEM-EDS tests show that loess specimens retain granular, trellis pores, contact-cement microstructure after modification. The surface of loess particles became rough and floc was adsorbed after adding potassium silicate material. The EDS data represents that the K element content increases with the increasing of incorporation of potassium silicate. And the unconfined strength of specimens is positively correlated with the percentage of K element. It is also shown that connection strength of soil particles and the structure morphology are the main factors of the macroscopic mechanical properties of loess. The mechanism of loess reinforcement by compound modified sodium silicate is reinforcement of the bond strength of cement in microstructure and formation of three-dimensional networks of frame.