再生混凝土材料及其构件的阻尼性能与阻尼机理研究

Recycled concrete has being a research focus at home and abroad, but its damping capacity and damping mechanism is not yet clear.This research will be carried out in two levels, i.e. material level and structural member level, and also will combine theoretical study and experimental test. The effects of several factors on the damping of recycled concrete and its components will be systematically studied. These factors include replacement ratio, quality and gradation of recycled aggregates, kinds of modified admixtures, and damage degree. The research procedure is shown as follows: First, the effects of various factors on the damping of recycled concrete in elastic stage will be tested on the Self-developed three-point bending damping experimental device, and a stress-dependent damping model will be established. Second, the low cycle hysteretic test and the damped free vibration testing of recycled concrete cantilevers in several damage degrees will be performed to gain the equivalent viscous damping ratio and dynamic damping ratio, respectively, and the comparative analysis of the equivalent viscous damping ratio and dynamic damping ratio will also be conducted. Moreover, the theoretical relationship between the inelastic damping of recycled concrete members and the damage index will be build up. Finally, the morphology, composition and micro-hardness of the interfacial transition zone between recycled aggregate and hardened cement mortar will be evaluated by SEM, XRD, and micro-hardness tests. Then the damping mechanism of recycled concrete and its components will be discussed based on microscopic testing results. Therefore, the process of recycled concrete popularly used for structural materials would be accelerated by this research, and the results are valuable for design and dynamic characteristics analysis of recycled concrete structures.

再生混凝土新技术已成为国内外研究的热点，但其阻尼性能和阻尼机理尚未明确。本课题将在材料和构件层面，通过理论和试验相结合的方法，系统研究再生骨料取代率、品质、级配、改性掺合料、损伤等对再生混凝土材料及其构件阻尼性能的影响规律及阻尼机制。首先，通过自主研发的三点弯曲梁阻尼实验装置测试弹性阶段再生混凝土材料的阻尼性能，建立材料应力相关阻尼模型。其次，对再生混凝土构件分级低周滞回加载和自由振动衰减试验，分别测得不同损伤等级下的塑性破坏耗能和动态阻尼耗能，对比分析两者的定量关系，并建立再生混凝土构件非线性阻尼与损伤指数的理论关系。最后，微观试验研究再生骨料与硬化水泥砂浆界面过渡区的形貌特征、成分和显微硬度，深入探讨材料微观结构变化对宏观阻尼的影响机理。通过上述研究，可加快推进再生混凝土用作最大宗结构性材料的进程，实现再生混凝土的综合改性，为再生混凝土结构设计及其动力特性分析奠定坚实基础。

随着工业化的发展，大量天然砂石资源被消耗，同时产生了数量惊人的建筑废弃物，极大地破坏了生态环境，因而混凝土材料的可持续发展极其重要，再生混凝土新技术成为国内外研究热点，但其阻尼性能和阻尼机理尚不明确。本项目试验研究了再生骨料取代率、粒径、改性掺合料等对再生混凝土材料及其构件阻尼性能的影响；理论研究了再生混凝土材料阻尼与工作应力、构件阻尼与损伤发展的关系，对比分析构件塑形破坏耗能和动态阻尼耗能；并基于再生混凝土界面过渡区特性、裂缝发展规律探讨再生混凝土材料及其构件的阻尼机理。研究结果表明：弹性阶段再生混凝土材料的损耗因子相比于天然骨料混凝土增长不超过10%；再生混凝土悬臂梁阻尼比随损伤指数先增大后减小，峰值阻尼比是初试弹性阶段阻尼比的2~3倍；损伤指数相同时，再生混凝土悬臂梁阻尼比随再生粗骨料取代率的增加而增大，随再生粗骨料粒径的减小而增大；再生混凝土悬臂梁阻尼性能和损伤指数的演变与悬臂梁裂缝数量、开展高度及宽度的发展密切相关；构件耗散因子不仅与工作应力幅值有关，且与构件截面形式、荷载类型、荷载位置有关；再生混凝土动态阻尼耗能与塑形破坏耗能比值随荷载增大而增大，动态阻尼耗能与塑形破坏耗能基本相当；再生混凝土孔隙比表面积和累计孔体积大于天然骨料混凝土；再生混凝土悬挂梁阻尼比与裂缝面积比率相关；界面过渡区的滑动、微观裂缝的发展、孔隙内空气的缩胀及宏观裂缝界面间的摩擦均增加了再生混凝土阻尼耗能。本项目研究为推进再生混凝土用作最大宗的结构性材料及再生混凝土结构设计与其动力特性分析奠定基础。