偏高岭土与石灰协同稳定团状红黏土的耐久性研究

The durability of lime stabilized laterite soils deteriorates, inducing a large number of projects disease. This programme research route is from testing, analysis, modeling to application, which combines macro-microscopic tests and theoretical analysis methods. Durability tests are carried out on different size agglomerate laterite soils treated with metakaolin and lime. There are two kinds of experimental conditions. One of them is under different times of drying-wetting cycles and freezing-thawing cycles effect, and the other is under different pH solution immersion. The former obtains durability of metakaolin-lime stabilized soils by using high-low temperature experiment instrument to simulate climate effect, and the later gains durability by soaking in acid or alkaline solution to simulate lime-laterite soils interaction. Moreover, micro-information about cemented states of treated soils, such as pore size distribution, ion concentration and so on, which would be captured by pore analyzer, atomic absorption spectrometer, et al. These information are used to analyze intrinsic reasons on properties degraded induced by environment influence, and also to reveal mechanism of metakaolin synergistic effect on its durability. Based on damage mechanics theory, durability prediction models of metakaolin-lime treated laterite soils will be established. It’s significant to improve the durability of treated laterite soils both in theoretical and practical aspects.

石灰稳定红黏土耐久性发生劣化，会诱发大量工程病害。项目遵循“试验→分析→建模→应用”的整体思路，采用宏-微观试验与理论分析相结合的方法，以不同团粒尺寸的红黏土为对象，开展偏高岭土与石灰协同稳定团状红黏土的耐久性研究。利用高低温智能控制箱模拟气候周期作用，获得不同干湿、冻融循环次数作用下稳定团状红黏土耐久性的演化规律；通过制备酸碱溶液浸泡模拟石灰-红黏土互损作用，获得不同pH值溶液浸泡下稳定团状红黏土耐久性的演化规律。借助孔隙分析仪、原子吸收光谱仪等设备，捕捉表征胶结质赋存状态的孔隙分布、离子浓度等关键细微观信息；分析干湿、冻融和石灰-红黏土互损等因素引起稳定红黏土耐久性劣化的本因；同时揭示偏高岭土对其耐久性增效的机制。以损伤力学理论为基础，建立偏高岭土-石灰稳定团状红黏土的耐久性预测模型。从而，在理论上为稳定红黏土耐久性的增效提供科学依据；在应用上为稳定红黏土工程的养护维修提供决策支持。

红黏土是一类特殊性黏土，天然含水率高导致难以压实；易于成团使得掺石灰等处治时拌合不均匀；另外，红黏土还呈弱酸性，石灰-红黏土将发生缓慢的互损作用。为此，项目围绕以上三个关键问题，开展了石灰-红黏土互损行为、团粒尺寸效应、干湿循环效应、抑制水敏性的力学响应，以及偏高岭土增强石灰处治红黏土耐久性的机理等研究。研究发现，石灰-红黏土互损引起处治红黏土的强度衰减，酸性溶液作用下石灰处治红黏土被溶蚀，团粒间孔隙会增大。红黏土掺入5%石灰和5%偏高岭土，养护120d可以获得较好的力学性能。团粒尺寸也会影响处治成效，红黏土团粒尺寸越大，石灰只能附着于团粒表面，仅形成团粒间连接，处治效果相对不明显；但掺入5%偏高岭土后可以对冲团粒尺寸的不利影响。处治红黏土受干湿循环作用，其强度会衰减；相同石灰和偏高岭土掺入比，团粒尺寸小的处治红黏土，经历18次干湿循环作用后，其强度衰减幅度相对较小。压实红黏土因失水衍生微裂隙，无侧限抗压强度随含水率降低，呈现先增大后减少的变化规律，但掺入石灰-偏高岭土后，虽有小幅度降低，但接近完全干燥时，其强度又会增大，有效抑制了红黏土收缩效应，提高其整体强度。究其原因，偏高岭土含有大量无定形的硅、铝氧化物，具有高“火山灰”活性，可以快速捕捉水化石灰中的钙离子，形成硅、铝酸钙等胶结物。其最终的生成物不同于传统以离子键结合的硅酸盐，而是形成了以共价键结合的网状胶结物。此外，偏高岭土不仅促进石灰处治土形成化学胶结，还起到了充填团粒间孔隙的作用。研究结论可为红黏土分布地区的工程建设提供科学参考。