全级配混凝土的变形破损机理及力学特性尺度效应研究

Full-graded concrete is widely used in large-scale hydraulic projects. Its mechanical properties are studied with theoretical analysis, physical experiment and numerical simulation. This study focuses on deformation damage mechanism and mechanical property size effect. A 3D numerical analysis model is established for concrete damage behavior simulation. In this model, concrete is divided into cement mortar, aggregates and their interfaces in mesoscopic level, and cracks are simulated with the theory of fracture mechanics. The model is calibrated and verified by physical experiments firstly, and then used to simulate full-graded concrete behaviors under the loads of tension, compression and splitting. The simulated results are studied to figure out the concrete deformation damage mechanism as well as the relationship between aggregate characteristics (i.e. size and density) and concrete macroscopic mechanical parameters (i.e. elastic modulus, possion’s ratio and strength). The simulated results and the physical experiment results are used to establish the quantitative relationship between the concrete specimen size and the macroscopic mechanical parameters using artificial intelligence methods. In this study, an efficient and economic approach is proposed to predict the mechanical properties of full-graded concrete. This approach is able to quantitatively evaluate the service capacity of hydraulic concrete and thus has a broad application prospect.

本项目以大型水利水电工程中广泛采用的全级配混凝土的力学特性为研究对象，采用理论分析、物理试验与数值模拟相结合的方式，研究其变形破损机理及尺度效应。首先对混凝土中砂浆、骨料及界面进行离散，以断裂力学作为裂纹扩展判据，并通过物理试验的参数标定及验证，基于复合单元法建立细观尺度下的混凝土破损三维数值分析模型。通过对一系列大尺度全级配混凝土试件的变形破裂过程进行细观分析，揭示拉、压、劈裂荷载下全级配混凝土的变形破损机理，研究骨料粒径、骨料密度与混凝土宏观力学参数（弹模、泊松比、强度）之间的相关关系。基于物理试验以及大量数值试验的结果，采用人工智能方法，建立试件尺度与宏观力学参数之间的定量联系。研究成果为推测全级配混凝土的力学性能提供一条有效且经济的途径，并为量化评价水工混凝土结构的服役性能提供依据和方法，具有广阔的应用前景。

全级配混凝土是重力坝、拱坝等大体积水工建筑物的核心建筑材料，其力学性能直接影响建筑物的稳定与安全。全级配混凝土由于试件尺寸较大，因此物理试验的难度较大、设备要求较高。设计中，一般采用湿筛二级配小试件的试验结果来推测全级配混凝土大试件的力学性能，但是两者之间存在较大差异，即存在显著的“尺度效应”。本项目采用统计分析、物理试验与数值模拟相结合的方式，针对全级配混凝土的力学性能、尺度效应的影响程度及影响因素等问题开展研究。共搜集了11个工程共209组试验数据，采用统计方法对试验结果进行了分析，研究了全级配混凝土与湿筛二级配混凝土的单轴抗拉强度比值、单轴抗压强度比值、劈裂抗拉强度比值（以下均简称为抗拉强度比值、抗压强度比值、劈拉强度比值）的分布规律及参考取值，对比了圆柱体试件与立方体试件对抗压强度比值的影响，改进了抗压强度比值随龄期变化的经验公式。提出了裂缝扩展释放算法，据此建立了混凝土细观数值模拟方法，并论证了方法的可行性。采用该数值模拟方法，研究了龄期对全级配混凝土抗拉性能的影响，构建了抗拉强度、弹性模量随龄期变化的函数公式。采用该数值模拟方法，进一步对比了全级配混凝土与湿筛二级配混凝土的抗拉性能以及裂缝扩展过程，构建了抗拉强度比值、弹性模量比值随龄期变化的函数公式，通过数值结果与统计结果的对比，发现规律基本一致。