混凝土I-型细观断裂模型及其在材料层次#br# 尺寸效应中的应用

混凝土材料的断裂破坏本质上是内部微细裂纹在荷载作用下不断萌生、扩展以及贯通的结果，断裂裂缝在细观层次上则是由砂浆裂缝、界面裂缝以及骨料裂缝3部分组合而成。文章基于细观力学和断裂力学基本理论，建立一类能够同时考虑细观裂缝在混凝土材料内部扩展过程中绕过骨料和穿透骨料发展的混凝土I 型细观断裂模型。与已有试验数据对比表明，文章模型能够有效预测混凝土断裂能等宏观力学参数随细观组分力学性能的变化规律。进而，基于建立的细观断裂模型，初步分析混凝土材料层次的强度尺寸效应，结果表明：当砂浆力学性能确定时，混凝土材料的名义强度与骨料强度和界面强度正相关；界面的力学性能能够显著影响混凝土材料名义强度等宏观力学参数随骨料尺寸的变化规律；高性能混凝土强度随骨料尺寸增大而增大，普通性能混凝土强度随骨料尺寸增大而减小。文章模型分析方法以期为基于性能设计的混凝土配合比研究奠定理论基础。

Concrete mode-I mesoscale fracture model and its application in#br# analysis of size effect at material level

The fracture failure of concrete is essentially caused by the propagation and coalescence of micro-cracks inside the material under loading. At mesoscale，the fracture crack could be regarded as the combination of mortar crack，bond crack and aggregate crack. This paper establishes a mode. I mesoscale fracture model for concrete which could take both intergranular and transgranular crack pattern into consideration based on mesomechanics and fracture mechanics.The proposed model could efficiently predict the variation of concrete fracture energy with properties of meso components based on existed test data. In addition，the size effect at material level of nominal strength of concrete is preliminarily analyzed based on the proposed mesoscale fracture model. The results show that，for a determined mortar matrix，the nominal strength of concrete has positive correlation with that of aggregate and matrix-aggregate bond; mechanical properties of matrix-aggregate bond can significantly affect the nominal strength of concrete and other macroscopic mechanical parameters with aggregate size; for high-performance concrete，the nominal strength increases with increasing aggregate size，while for normal-performance concrete，the nominal strength decreases with increasing aggregate size. The model analysis method proposed in this paper can lay a theoretical foundation for the research of concrete mix proportion based on performance design.