偏高岭土地聚合物膨胀改性及其修补混凝土裂缝的作用机理

Cracking is one of the major reasons for the degradation of concrete structures, and is also one of the critical issues in civil engineering. This project aims to modify the expansibility of metakaolin-based geopolymer (MK material) through the incorporation of nano-SiO2, and to investigate the performance and mechanism of applying the modified MK material in the mending of concrete cracks. The expansibility of MK materials is adjusted and controlled through alkali-silica reaction (ASR), which is based on its expansion mechanism in normal concrete. The ASR is trigged by introducing nano-SiO2 into geopolymerisation system and the reaction characteristics of nano-SiO2 in the strong alkaline environment and the coupling effect in alkaline activation will be investigated. The performances of this expansion-controlled MK material in mending concrete cracks and the key parameters will be analyzed by evaluating the binding and compatibility with concrete. The advanced techniques will be adopted to investigate the polymerization state of [SiO4] and [AlO4] tetrahedron, the diffusion and distribution of Ca, Si and Al, and the nanostructure in binding interface. In combination with the reaction kinetics and surface adsorption-diffusion mechanisms, the binding property between MK material and concrete cracks will be revealed, and the mechanisms of nano-SiO2 modified MK materials for mending concrete cracks will be illustrated. This project is expected to change the conventional methods of mending concrete cracks by physical filling, and propose a new chemical binding method with high efficiency.

混凝土裂缝是导致混凝土结构性能劣化的主要原因之一，也是土木工程领域面临的重要课题之一。本项目拟通过纳米二氧化硅对偏高岭土地聚合物(MK材料)的膨胀改性，研究将其应用于混凝土裂缝修补的性能和作用机理。基于混凝土碱硅酸反应(ASR)膨胀原理，通过加入纳米二氧化硅诱发ASR膨胀效应的方法，调控MK材料膨胀性能，并对强碱环境下纳米二氧化硅反应特性及其与碱激发反应的耦合效应进行研究。结合胶结力测试和相容性评价等方法，对MK材料修补混凝土裂缝的性能及其主要影响因素进行研究。采用现代分析方法对胶结区域硅氧、铝氧四面体的聚合状态，Ca、Si、Al等元素的扩散分布特征，产物形貌和组成等进行研究，并结合反应动力学原理和界面吸附扩散原理，探究MK材料与混凝土裂缝的界面结合特性，阐明纳米二氧化硅改性MK材料修补混凝土裂缝的作用机理，以期改变物理式填充修补混凝土裂缝的常规方法，提出化学胶结高效修补的新思路。

混凝土裂缝是造成结构物承载能力、耐久性及防水性能降低的主要原因之一，是目前乃至将来土木工程领域必须面临的重要问题。本项目以偏高岭土地聚合物为基本材料，在采用纳米二氧化硅解决其收缩率大问题的基础上，对其应用于混凝土裂缝修补的性能及作用机理进行研究，取得了较好的研究成果。（1）以纳米二氧化硅为膨胀剂实现了偏高岭土地聚合物的膨胀性能：探究了纳米二氧化硅的性能参数、掺量及环境因素等条件与地聚合物膨胀性能间的关系，并与氧化镁、氧化钙类膨胀剂进行比较。（2）揭示了纳米二氧化硅引起偏高岭土地聚合物膨胀作用的机理：在地聚合物反应的强碱环境中，活性二氧化硅与碱激发剂溶液发生碱硅酸反应生成硅酸盐凝胶相，吸水后发生肿胀造成地聚合物膨胀效应的产生。（3）明确了偏高岭土地聚合物与水泥石间的高效胶结性能，并对其作用机理进行研究：偏高岭土地聚合物与水泥石间形成一体化胶结，胶结强度明显高于水泥浆体，胶结界面区域连续、致密，两者间形成化学胶结效应。项目研究成果的取得可为地聚合物收缩问题的解决及混凝土裂缝修补提供材料和技术支持，具有较强的理论意义和实际应用价值。