大粒径再生混凝土初始损伤定量分析及性能退化机理

Recycled concrete is a green and sustainable building material, which is made of crushed waste concrete structure and replaced by natural aggregate. Its internal micro-crack distribution is more complex and its macro-performance deteriorates to a certain extent. In order to study the damage mechanism and improve the quality of recycled concrete, the following tasks are planned: using micro-test method and image analysis technology, the micro-cracks and pore distribution in concrete with different recycled aggregate sizes are studied, and the initial damage distribution characteristic parameters of recycled concrete are quantitatively analyzed; micro-micro-macro experiments are carried out and micro-numerical simulation method is established. Considering the effect of initial defects and recycled aggregate, the meso-numerical model of concrete is established. The damage evolution process of recycled concrete is simulated by combining meso-numerical simulation and macro-mechanical properties test. The relationship between the properties of recycled concrete and the particle size, properties and dosage of recycled aggregate, the distribution of initial defects, the interface between recycled aggregate and mortar and the properties of mortar matrix is studied. The results show that the relationship between the composition, structure and performance of recycled concrete is analyzed, the deterioration law of recycled concrete performance is explored, and the failure mechanism of recycled concrete with large particle size is revealed. The expected results can provide scientific basis for the popularization and application of recycled concrete in hydraulic engineering.

再生混凝土由废弃混凝土结构粉碎后替代天然骨料浇筑而成，是一种绿色可持续发展建筑材料，其内部微裂纹分布更加复杂且宏观性能有一定程度劣化。为研究其破坏机理，提升再生混凝土工程质量，课题拟开展以下工作：采用微观试验方法和图像分析相关技术，研究不同再生骨料粒径混凝土内部微裂纹和孔隙分布，定量分析再生混凝土初始损伤分布特征参数；开展微-细-宏观试验，结合细观数值模拟方法，建立考虑初始缺陷和再生骨料作用的混凝土细观数值模型；结合细观数值模拟和宏观力学性能试验，模拟再生混凝土损伤演化过程，研究再生骨料粒径、性能和掺量、初始缺陷分布、再生骨料-砂浆间界面和砂浆基体性能等因素和再生混凝土性能间联系；结合不同尺度研究结果，分析再生混凝土组成、结构和性能间关系，探索再生混凝土性能劣化规律，揭示大粒径再生混凝土破坏机理。预期成果可为再生混凝土在水利工程中的推广应用提供科学依据。

再生混凝土作为一种低碳绿色建筑材料，解决了新老建筑物更替而引发的建筑废弃物堆积等社会与环境问题，此外还有效缓解了当前紧张的优质天然骨料供需矛盾，应用前景广阔。本项目围绕大粒径再生骨料混凝土的微-细-宏观力学性能等方面开展了研究。（1）研究了4类再生粗骨料和天然骨料的形状和物理性能的差异及其对混凝土基本力学性能的影响。结果表明：再生粗骨料表观形状同时受母材特性和生产工艺的影响；机械研磨除浆可以显著改善再生粗骨料品质，残余砂浆含量对再生粗骨料物理性能有不利影响；粗骨料吸水率更高、压碎指标更大且密度更低的再生混凝土，其28d抗压和劈裂抗拉强度较普通混凝土可以分别提高5.5%和5.0%；随着粗骨料球度和均匀度的增大，混凝土强度随之提高。（2）研究了4类再生粗骨料混凝土的微观结构特征。结果表明：4类再生混凝土水化产物种类相同，但14d龄期前的微观结构致密性较普通混凝土更差，在14d~28d龄期时，再生混凝土内部再次出现发育中的水化产物，这期间混凝土致密性得到有效改善；（3）研究了再生混凝土界面微观结构，定量分析了再生混凝土初始损伤，基于微观结构试验结果，建立了考虑真实结构的再生混凝土细观数值模型。（4）为研究大粒径再生混凝土损伤演化过程及断裂机理，从宏观方面探究了变温、变湿环境下大粒径再生混凝土的基本力学性能和断裂性能。结果表明：环境湿度保持不变，当温度高于零摄氏度时，随着温度的升高，再生混凝土的强度逐渐减小；环境温度保持不变，随着湿度的增加，再生混凝土的强度先增大后降低，高湿度环境有利于再生混凝土强度的发展。环境温度保持不变，随着湿度的增大，再生混凝土断裂韧度及断裂能先增大后降低，湿度为75%时达到最大。