再生混凝土动态直剪力学性能及其应变率敏感性机理研究

Due to the complex source of Recycled Coarse Aggregate (RCA), the old cement mortar attached to RCA surfaces and micro-cracks produced in the crushing process, the mechanical properties and structural properties of Recycled Aggregate Concrete (RAC) are typically different from conventional concrete made with the same mixture proportions. The characteristics of RCA have a certain impact on adhesion, crack propagation path and interfacial shear transfer behaviour. The research on dynamic direct shear mechanical behaviors of RAC and the mechanism of strain-rate sensitivity of RAC under direct shear loading is limited. This research will focus on the analysis of structural members level and material level, the experimental research, simulation analysis and theoretical study were conducted to investigate the effects of strain rate on direct shear behaviors of RAC members and RAC material..The research procedure is listed as follows:.Firstly, an experimental research on RAC push-off specimens will be carried out to study the effect of strain rate on maximum direct shear stress, shear slip, shear stiffness and failure patterns of RAC push-off specimens with stirrups..Secondly, aiming at the material properties of RAC, the dynamic direct shear mechanical behaviors of RAC without stirrups were experimental studies. .Then, with the reference of the experimental study on the dynamic direct shear mechanical behaviors of RAC material, the variation micro and meso-structure of shear plane will be evaluated by high magnification microscope. Then mechanism of strain-rate sensitivity of RAC under direct shear loading will be analyzed theoretically..Finally, a finite element model based on modeled RAC will be established. The strain-rate sensitivity of all phase materials and its influence on the strain-rate sensitivity of direct shear mechanical behaviors of RCA will be discussed..This research can make up an insufficient in dynamic direct shear mechanical behaviors of RAC. And the results will provide the theory foundation for shear design of RAC structure members and the RAC structural response analysis under dynamic direct shear loading.

由于再生骨料来源复杂、表面附着老砂浆及骨料表面存在微裂缝等特性，再生混凝土的力学性能及结构性能通常与同配合比下的普通混凝土存在一定差异。再生骨料的特征对于界面粘结力，裂缝开展及界面剪力传递都产生一定的影响。目前再生混凝土动态直剪力学性能及其应变率敏感性机理仍不明确。本项目将从不同研究尺度上，通过试验、仿真和理论分析相结合的方法，系统地研究再生混凝土构件及材料的直剪性能应变率敏感性规律。首先通过对再生混凝土Z型试件进行直剪试验，分析不同应变率下配筋再生混凝土构件的最大直剪应力、剪切滑移、剪切刚度和破坏形态等变化规律。然后针对再生混凝土材料性能，通过对素混凝土试件进行直剪试验，分析再生混凝土材料的动态直剪性能。随后，在素混凝土试验的基础上，通过细微观试验获得破坏后剪切面骨料断裂情况，进而研究应变率效应对于再生混凝土动态直剪性能的影响机理。最后基于模型骨料再生混凝土概念建立数值模型，模拟细观各相材料的率敏感性及其对于再生混凝土直剪性能应变率敏感性的影响。上述研究，可弥补再生混凝土动态直剪性能研究的不足，为再生混凝土结构构件抗剪设计及其动态直剪荷载下的结构反应分析奠定基础。

本项目基于建筑固体废弃物的综合利用及再生混凝土工程应用的广泛前景，对再生混凝土动态直剪力学性能开展系列研究。本项目对预裂再生混凝土无腹筋试件进行直剪试验，系统分析了再生粗骨料取代率、混凝土强度及应变率等因素对于再生混凝土试件直剪性能影响规律；并在此基础上开展再生混凝土剪力传递理论分析，基于Walraven提出的骨料咬合模型及再生粗骨料特性，提出了适用于再生混凝土的修正理论模型；通过未预裂试件直剪试验，研究了未预裂试件在直剪荷载作用下裂缝发展规律及受力机理，分析了高应变率下再生混凝土骨料粒径对其剪切性能影响；对未预裂试件低应变率下剪切性能进行了数值模拟及变参数分析，获得了低应变率下未预裂再生混凝土试件剪切应变-位移特征曲线；通过模型骨料混凝土直剪试验，研究骨料分布对直剪性能影响，揭示了再生混凝土直剪荷载作用下裂缝发展规律及破坏模式。此外，通过对再生混凝土粉及再生混凝土性能研究，初步探索了多尺度再生材料的利用。