Significance of Paste-Sand Interfaces in Micromechanical Behavior of Concrete

本研究的目的是将材料科学与结构工程相结合，在评价水泥浆体-砂粒界面在单轴受压混凝土应力-应变行为中的定性和定量意义和作用的基础上，引入一种新的方法来研究混凝土的微观力学行为。在试验部分，对具有不同填充特性的砂粒的砂浆圆筒进行了应力-应变行为和细观力学性能的测试。混凝土圆柱体也将进行测试，以比较粗集料和沙粒的重要性。然后使用具有背向散射电子分析和图像分析能力的扫描电子显微镜、汞渗透孔度计和电导率测量技术将这些特性与微观结构特性相关联。在分析部分，建立了描述混凝土细观力学行为的模型，并定量地定义了界面参数的作用和意义。在模型的建立过程中，采用了非线性断裂力学方法，以有限元方法为工具，分析了裂纹的扩展和局部变形。将研究裂纹扩展与砂粒堆积特性的关系。在这种方法中，界面被视为弱面或初始缺陷。这项研究的结果可以推广到其他情况，包括耐久性、徐变和收缩考虑因素，以及传统和先进水泥基混凝土复合材料的最佳配合比。

The objective of the proposed investigation is to introduce a new approach to the study of the micromechanical behavior of concrete by combining its materials science and structural engineering aspects, based on the assessment of the qualitative and quantitative significance and role of cement paste-sand particle interfaces in stress-strain behavior of concrete that is subjected to pure uniaxial compressive force. In the experimental part, mortar cylinders having sand particles of different packing characteristics are tested for their stress- strain behavior and their micromechanical properties. Concrete cylinders will also be tested to compare the significance of the coarse aggregate with the sand particles. These are then correlated with the microstructural properties using SEM with backscatter electron analysis and image analysis capabilities, mercury intrusion porosimetry, and electrical conductivity measurement techniques. In the analytical part, a model is developed which describes the micromechanical behavior of concrete and defines quantitatively the role and significance of interfacial parameters. In the model development a nonlinear fracture mechanics approach is taken using the finite element method as a tool to analyze crack propagation and localized deformation. The relationship between crack propagation and sand particles packing characteristics will be studied. In this approach, interfaces are treated as weak planes or initial flaws. Results of this investigation can be extended to other cases including durability, creep, and shrinkage considerations, and optimum mixture proportioning of conventional and advanced cement-based concrete composites.