基于级配和胶凝作用的水泥土强度形成机制与调控技术

The engineering properties of cement-stabilized soils are focused in the practice of soft clay foundation modified by the deep mixing method. However, their strengthes, are obviously less and of larger variability than that of concrete and mortar for the natural gradation and clay minerals. To improve and standardize the strength behavior of the cement-stabilized soft clays, the contribution mechanism of the inert component (silt/sand fraction) to the strength and interaction between the clay minerals and the hydration products of the cement-based materials are systematically investigated by the advanced methodology of the modern concrete material science. The cement-stabilized soils are first prepared by the soft clays with the artificially adjusted gradation and clay minerals and by the cement-based materials with the regulated hydration products. Hereafter, after the preset curing periods, the macro tests (including the strength and pH value etc.), micro tests (including SEM/EDS, XRD/EDS and CT etc.), nano tests (including nano indentation, NID and atomic force microscope, AFM ) and materials indentation tests ( including XRD and 28Al/29Si NMR) are designed. With the above testing, the multiscale analysis models by XFEM methods, on the cementation materials from nano to micro scale and on cement-stabilized soils from micro to macro scale will be established. After these theoretical, experimental and numerical analyses, the gradation and cementation mechanism on the strength generation of cement-stabilized soft clay can be clarified, and the design procedure of the optimal cement component and silt/sand fraction of the artificial clay based on the gradation and clay mineral of the original soft clays will be proposed. At the end, the theoretical and laboratory investigation will be verified by the insitu case study. Above all, these results are helpful and valuable to deepen the cognition of strength generation of cement-stabilized soft clays and optimize the design procedure of this kind of materials.

水泥土的工程特性是软黏土地基搅拌桩加固实践中关注的重点，但与同为水泥基材料的混凝土和砂浆相比，具有强度低且变异大的特征，其主要原因与软黏土天然级配以及黏土矿物相关。针对水泥土强度提升和材料标准化问题，本研究围绕惰性组分（粉砂粒组）对水泥土强度的贡献机理，以及黏土矿物与水泥水化产物间作用机制这两个核心，引入现代混凝土材料多尺度研究体系，通过掺入海砂等细粒材料调控软黏土级配、调整水泥成分控制以水化产物与黏土矿物反应两种方法制备水泥土，开展宏观的物理力学、微细观的孔径与惰性组分分布、纳微观的物质成分与强度等测试，构建纳微观到微细观的胶凝产物、微细观到宏观水泥土的多尺度计算模型。通过分析与计算，阐明水泥土强度形成中级配与胶凝作用机制，形成基于软黏土的级配与矿物成分为初始条件的固化材料和惰性组分的调控设计方法。研究成果在深化水泥土强度形成机制的认知和促进水泥土材料的设计体系形成上具有重要的意义。

本研究围绕固化土中级配与水相作用机制和水化产物-黏土矿物相互作用两个核心，引入现代混凝土材料成套研究体系，通过掺入细粒材料调控软黏土级配、调整水泥成分控制水化产物与黏土矿物反应，形成基于软黏土的级配与矿物成分的固化土强度调控设计方法。研究首先以砂和铁矿尾泥作为粉/砂粒组调控材料，开展了掺砂固化土室内试验，明确粉砂粒组对于固化土胶凝强度、摩擦行为和耐久性的影响，结合微观试验和数值模拟，揭示粉/砂粒组在固化土中的作用机理，进行了不同初始含水率的固化土强度试验，查明固化土中的水分作用机制。然后，通过硅粉调控胶凝、发泡调控密度这一思路，提出了固化土强度定量解译方法，从密实层面研究了膨胀性功能组分对固化软土性能的影响，从胶凝层面研究水泥熟料组分与黏土矿物间的相互作用，采用微观测试方法，揭示了水化产物-黏土矿物相互作用过程、反应生成物矿相组成和微观孔隙结构的演化特性，并通过解卷积统计分析对物质相进行定量鉴别，明晰了水化产物-黏土矿物相互作用内在机理。最后，提出了固化联合真空脱水加固软土的工艺，验证了该方法的可行性，此外，提出了固废基固化剂组分调控框架，并结合现场试验论证了所提框架的效果。研究成果在深化水泥土强度形成机制的认知和促进水泥土材料的设计体系形成上具有重要的科学价值。