碱激发对砒砂岩地聚物水泥复合土强度及微观结构的影响机理

    Influence mechanism of alkali excitation on strength and microstructure of Pisha Sandstone geopolymer cement composite soil

    • 摘要: 为防治水土流失,提高以砒砂岩为基础原料水泥土的力学性能,实现大量松散砒砂岩在实际工程的有效利用,通过无侧限抗压强度试验和压汞、X衍射物相分析、扫描电镜、傅里叶变换红外光谱等方法,探究碱激发对砒砂岩地聚物水泥复合土强度及微观结构的影响机理。结果表明:N-A-S-H(水化硅铝酸钠)凝胶含量是影响复合土强度的主要因素,其含量受碱激发温度及碱当量的影响。碱当量的增大及碱激发温度的提高,可促使砒砂岩中的蒙脱石、石英以及偏高岭土发生溶蚀,促进N-A-S-H凝胶的产生,但当温度超过80 ℃后会促进N-A-S-H凝胶向钾A型沸石晶体转化。碱当量增加使得强度增长速率先增加后减缓,在碱激发温度为80 ℃、碱当量为2%时,砒砂岩地聚物水泥复合土配比达到最优,此时复合土中生成N-A-S-H凝胶产物最多,<10 nm孔径占比最大(11.67%),孔隙率最低(23.47%),强度最高(8.23 MPa)。该研究可为砒砂岩地聚物水泥复合土在实际工程中的应用提供理论依据。

       

      Abstract: Abstract: Pisha Sandstone is well known as feldspathic Sandstone, soft rock, and montmorillonite-enriched Sandstone in the Ordos region of Inner Mongolia of China. A large amount of loose Pisha Sandstone serves as a typical engineering material for roadbed base, channel lining, or earth dam slope in most road paving, field drainage, or water transmission. In this study, the alkali-excited geopolymer cement composite soil with Pisha Sandstone as the base material was developed to improve the mechanical properties of cement soil for the further resource utilization of Pisha Sandstone. A universal material testing machine was also selected to explore the effect of alkali excitation on the mechanical properties of composite soil at the various temperatures of alkali excitation and equivalence. A mercury-pressure test was carried out to clarify the time-varying characteristics of pore structure. Subsequently, X Diffraction Pattern (XRD) was utilized to identify the crystal composition, while, Fourier Transform Infrared (FTIR) spectroscopy was used to determine the changes of atomic structure in chemical reactions. The positions of different absorption peaks in XRD and FTIR were selected to evaluate the degree of chemical reactions. A Scanning Electronic Microscope (SEM) was also used to characterize the morphology of composite soil. The results revealed that the temperature of alkali excitation and alkali equivalent behaved a great positive influence on the mechanical properties of Pisha Sandstone geopolymer hydroclay. The micromechanical data show that the N-A-S-H gel content as a main factor significantly altered the pore structure and strength of Pisha Sandstone geopolymer cement composite soil. In turn, the N-A-S-H gel content depended mainly on the temperature of alkali excitation and alkali equivalent, similar to the dissolution of some montmorillonite, quartz, and metakaolin in Pisha Sandstone. In addition, the free SiO32- and AlO32- substances promoted the production of N-A-S-H gel in alkali environment. However, the transformation of N-A-S-H gel to potassium A zeolite was promoted significantly to cause the decrease of strength, when the temperature exceeded 80 ℃. Since the N-A-S-H gel content changed the percentage of <10 nm pore structure of composite soil, the filling and cementing effect caused by the porosity of composite soil tended to decrease. Meanwhile, the percentage of large pores decreased, whereas, the percentage of small pores increased. An optimum ratio of composite soil was achieved at the alkali excitation temperature of 80 ℃ with 2% alkali equivalent. The greatest number of N-A-S-H gel products were generated in the Pisha Sandstone geopolymer cement composite during this time, particularly with the largest percentage of internal <10 nm pore size of 11.67%, the lowest porosity of 23.47%, and the highest strength of 8.23 MPa. The finding can provide a sound theoretical basis for the practical application of Pisha Sandstone geopolymer cement composite soil in engineering projects in northwestern China.

       

    /

    返回文章
    返回