随着城市建设及城镇化进程加快，旧房拆除、道路改造、桥梁重建等行为会产生巨量废弃混凝土。为实现废弃混凝土的循环再利用，以其制成再生粗骨料部分取代天然粗骨料，针对纳米碳酸钙改性、再生粗骨料取代率对混凝土力学性能和疲劳特性问题展开了研究工作，旨在为科学评价疲劳荷载环境下纳米改性再生混凝土的长期稳定性提供理论依据。主要研究工作如下：

（1）通过物理试验判定再生粗骨料为Ⅱ类，辅以坍落度试验完善了配合比设计。结果表明，再生粗骨料取代率Q越高，混凝土强度越低；纳米碳酸钙对再生混凝土强度及韧性有明显增强，纳米碳酸钙最优掺量N为1%；基于中心质效应对微观形貌分析，纳米碳酸钙促进水化反应，起到成核位垒、桥接作用。

（2）以静力加载、动态循环加载，对比分析了不同应力水平 下纳米碳酸钙及再生粗骨料取代率对抵抗疲劳特性的影响规律，探索了不同循环次数下疲劳剩余强度的表现规律。结果表明：再生粗骨料掺加对疲劳特性具有明显负面影响，再生混凝土对疲劳循环更加敏感；纳米碳酸钙可有效改善混凝土整体性，提高混凝土抵抗变形能力。

（3）基于统计学概率分布模型对疲劳寿命 进行分析，验证了两参数威布尔分布概率模型具有更高可靠性。基于威布尔分布模型得出了四种编组条件下双对数 曲线及相应疲劳寿命方程，深入研究了四种编组疲劳特性；考虑一定存活概率 下相对疲劳寿命建立了双对数 曲线及疲劳方程，对比静力强度及条件疲劳强度，进一步探究了四种编组混凝土疲劳次数关系：W2Q50

（4）研究结果表明疲劳应变演化符合三阶段应变曲线发展规律，对再生混凝土第二阶段疲劳应变吻合度较低，通过对疲劳应变研究提出新的方程来描述再生混凝土第二阶段应变曲线，且吻合度较高。引入变形量，建立了变形量与循环比函数关系。

With the acceleration of urban construction and urbanization, the demolition of old houses, road renovation, bridge reconstruction and other acts will generate huge amount of waste concrete. In order to realize the recycling of waste concrete, this paper partially replaces natural coarse aggregate with recycled coarse aggregate made from waste concrete, and conducts research work on the mechanical properties and fatigue characteristics of concrete by nano-modification and recycled coarse aggregate replacement rate, aiming to provide theoretical basis for scientific evaluation of long-term stability of nano-modified recycled concrete under fatigue loading environment. The main research works are as follows:

(1) The recycled coarse aggregate was determined as Class II by physical test, and the mix design was improved by slump test. The results show that the higher the replacement rate of recycled coarse aggregate Q, the lower the concrete strength ; the strength and toughness of recycled concrete are obviously enhanced by nano calcium carbonate, and the optimum content of nano calcium carbonate is 1 %. Based on the analysis of microstructure by central effect, nano calcium carbonate promotes hydration reaction, plays a role of nucleation barrier and bridging.

(2) With static loading and dynamic cyclic loading, the influence law of nano-modification and recycled coarse aggregate substitution rate on the resistance fatigue characteristics was compared and analyzed, and the performance law of fatigue residual strength under different cycle times was explored. The results show that: recycled coarse aggregate incorporation has a significant negative impact on fatigue characteristics, and recycled concrete is more sensitive to fatigue cycles; nano can effectively improve concrete integrity and increase concrete resistance to deformation.

(3) Based on the statistical probability distribution model, the fatigue life was analyzed, and the two-parameter Weibull distribution probability model was proved to be more reliable. Based on the Weibull distribution model, the double logarithmic curves and corresponding fatigue life equations were derived for the four grouping conditions, and the fatigue characteristics of the four groupings were investigated in depth; the double logarithmic  curves and fatigue equations were established considering the relative fatigue life under certain survival probability, and the relationship between the fatigue times of the four groupings of concrete was further investigated by comparing the static strength and the conditional fatigue strength: W2Q50

(4) The results show that the fatigue strain evolution is in accordance with the three-stage strain curve development law, and the agreement is low for the second stage fatigue strain of recycled concrete. A new equation is proposed to describe the second stage strain curve of recycled concrete through the study of fatigue strain, and the agreement is high. The deformation volume was introduced and the relationship between deformation volume and cycle ratio function was established.

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