考虑材料层次尺寸效应影响的混凝土力学性能理论预测方法

大坝混凝土粗骨料粒径范围为5~150 mm,混凝土材料的宏观力学性能易随骨料级配等发生变化。本文从细观角度出发,提出了一种能够考虑材料层次尺寸效应影响的预测混凝土宏观力学性能的理论分析方法。结合混凝土材料内部细观结构形式,将其看作由粗骨料颗粒、砂浆基质以及界面过渡区组成的三相复合材料。假定骨料颗粒在混凝土受力过程中不发生破坏,采用双线性本构模型描述砂浆基质和界面过渡区的材料力学行为,基于断裂力学基本理论框架,推导得到了混凝土细观裂缝长度、宏观断裂能、单轴拉伸强度、特征长度以及脆性指数等力学参数的理论公式。基于本文提出的理论预测方法,分析了界面过渡区力学性能以及粗骨料级配、含量对混凝土宏观力学性能的影响。

A theoretical method to predict the mechanical properties of concrete considering of the size effect in material

The particle size of coarse aggregates in dam concrete ranges from 5mm to 150mm, consequently, the macroscopic mechanical properties of concrete are easily varied with the aggregate gradation. From the mesoscopic of view,a theoretical method to predict the mechanical properties of concrete considering of the size effect in material is established. In view of the internal structures, the concrete material is regarded as a three-phase composite composed by the coarse aggregate,the mortar matrix and the interfacial transition zone (ITZ). It is assumed that the aggregate is unbroken within the process of loading. The mechanical behavior of the mortar matrix and the ITZ is described by bilinear constitutive models. Based on the theoretical concept of fracture mechanics, a group of theoretical formulae for the determination of mechanical parameters of concrete including the mesoscopic crack length,the macroscopic fracture energy,the uniaxial tensile strength, the characteristic length and the brittleness number are derived. The influences of the mechanical properties of the ITZ and the aggregate gradation/volume on the macroscopic mechanical properties of concrete are analyzed based on the proposed theoretical method.