冻融与干湿循环对无机材料固化硫酸盐渍土的固化反应及强度影响

Durability under the condition of freezing-thawing and wetting-drying cycles is one of the key evaluation index for solidifying materials and solidified sulphate salty soil used in northwest region.The effects of freezing-thawing and wetting-drying cycles on strength and solidification properties of sulphate salty soil will be studied, which are solidified by modification silicification and lime and fly-ash. The main contents are as follows: (1) conducting unconfined compressive strength tests and shear strength tests on solidified saline soils with different ages under normal curing and immersed water saturated conditions; (2) conducting unconfined compressive strength tests and shear strength tests on solidified saline soils with 28 days age under the condition of freezing-thawing and wetting-drying cycles, and obtaining strength properties and stress-strain properties and mass loss; (3) conducting capillary elevation tests by a soil column apparatus with salt and moisture content sensor, testing moisture and soluble salt distribution along the column of solidified saline soils with 28 days age ; (4) carrying out grain size analyzer and electron probe analysis(EPMA) and mercury intrusion porosimeter(MIP) and x-ray diffraction analysis(XRD) and X-ray photoelectron spectroscopy (XPS), testing particle size distribution and mineral composition and chemical constituents and microstructure of solidified saline soils with 28 days age, discussing effect of freezing-thawing and wetting-drying cycles on solidification and strength of sulphate salty soil improved by inorganic agents based on physical and chemical and mechanical properties. It is of great theoretical and realistic significance to enrich the content of geotechnical engineering chemistry and develop the new solidifying technology.

冻融循环与干湿循环下固化硫酸盐渍土的强度和耐久性是评价固化材料与固化土在西北地区可否良好使用的重要指标。 以不同配比的改性水玻璃、石灰和粉煤灰联合固化盐渍土，研究冻融循环与干湿循环下固化土的强度性能。开展正常养护及浸水饱和下不同龄期固化土的抗压试验和抗剪试验；进行28d固化土冻融循环与干湿循环下的抗压试验和抗剪试验，测试其强度变化、应力应变特征和质量损失；在28d固化土柱中埋设盐分和水分传感器，测试毛细水上升试验中不同位置处的易溶盐和含水率变化；采用自动粒度分析仪、电子探针、压汞仪、X射线衍射分析及X射线光电子能谱分析，对28d固化土的粒度、矿物、化学成分与新相物质、微结构等进行测试，通过颗粒连接方式和结构分布形态分析，结合强度变化规律，探寻冻融与干湿循环对无机材料固化硫酸盐渍土的固化反应及强度影响。 研究成果可丰富岩土工程化学理论，开发固化硫酸盐渍土的新技术。

冻融循环与干湿循环下固化硫酸盐渍土的强度和耐久性是评价固化材料与固化土在西北地区可否良好使用的重要指标。 项目主要研究水玻璃石灰粉煤灰固化硫酸盐渍土的配比、冻融循环与干湿循环下固化土的强度性能、固化土盐分水分的迁移特征和固化机理。在国家自然科学基金资助下，项目组进行了大量的理论研究、室内试验和模型试验工作，取得了一些重要成果和关键数据。.（1）采用石灰粉煤灰水玻璃联合固化硫酸盐渍土时，石灰含量不宜超过8%。当石灰含量小于8%时，联合固化的抗压和抗剪强度较单一材料固化土有大幅度提升；随水玻璃浓度的增加，固化土的强度几乎呈线性增长。（2）石灰粉煤灰水玻璃固化硫酸盐渍土限抗压强度随含盐量的增加先增大后减小，存在一个界限含盐量1.8%。（3）相对于压实盐渍土，固化盐渍土不存在冻胀现象；采用40℃改性的水玻璃时，固化盐渍土的抗干湿冻融耐久性能力最好；干湿冻融循环10次后固化盐渍土抗压强度损失率6.7％，15次以后损失率为15.2％。与此相比较，未固化盐渍土在13次循环后强度损失达到88%。（4）固化盐渍土中的毛细水迁移速率和Cl－、SO42-的迁移速率均小于压实盐渍土，说明固化盐渍土有减缓毛细水上升和阻碍盐分迁移的作用；在迁移过程中， Cl－迁移速率大于SO42-。试验说明固化硫酸盐渍土不仅具有强度上的提高，同时可以阻滞盐分，尤其是硫酸离子的向上运移。（5）固化硫酸盐渍土的微观机理解释：石灰粉煤灰能够改善盐渍土颗粒级配，缩小孔径范围，降低孔隙体积，进而提高抗压强度；水玻璃能够胶结土颗粒成为团聚体，减小孔隙率和孔隙体积，固化土抗压强度受浓度影响较大。水玻璃石灰粉煤灰固化土的孔隙特征不是最佳，但由于碱激发地聚物生成的水化凝胶物质填充了粒间孔隙，改善了颗粒胶结状况，抗压强度最高。本项目的实施，为硫酸盐渍土的工程资源化应用提供了有力的技术支撑。