混凝土界面过渡区对裂纹扩展过程的影响

Influence of Interfacial Transition Zone on Crack Propagation Process in Concrete

混凝土是由水泥砂浆、粗骨料和界面过渡区(interfacial transition zone,ITZ)组成的非均质复合材料。ITZ作为混凝土内部的最薄弱相,对混凝土的宏观断裂有重要影响。基于PFC 2D的FISH语言,建立了能反映混凝土骨料、水泥砂浆和ITZ等复杂细观结构的离散元模型,并探讨了在单轴压缩载荷下ITZ强度分布和强度值对混凝土裂纹扩展过程的影响。数值模拟结果表明:混凝土裂纹遵循从中心向加载端扩展的趋势,超过80%的裂纹出现在峰值应力后的软化阶段;ITZ强度分布对混凝土裂纹扩展过程影响较弱,当ITZ强度呈现U形分布时,混凝土中裂纹数量较多;ITZ强度值对混凝土断裂程度及最终断裂形式影响显著,当ITZ的最小黏结强度与砂浆黏结强度比p<0.5时,混凝土强度显著降低,且裂纹围绕混凝土模型中心分散扩展形成网状宏观裂纹,导致试件发生散碎破坏,当p>0.6时,裂纹从混凝土试样中心向加载端集中扩展形成宏观贯通裂纹,导致试件发生块状破坏。

Concrete is a heterogeneous composite material composed of coarse aggregate,mortar and interfacial transition zone(ITZ).ITZ is the weakest phase inside the concrete and has a significant effect on the macroscopic fracture process of concrete.To respectively explore the effects of the distribution and value of ITZ strength on the crack propagation process in concrete under uniaxial compression,a discrete element model that reflects complex mesostructures of concrete aggregate,mortar and ITZ is established in PFC 2D by the use of FISH code.The numerical simulation results showed that cracks follow the propagation order from the centre of concrete to the loading end during the crack propagation process,and more than 80%of cracks appear in the softening stage after peak stress.The ITZ strength distribution has a weak effect on the crack propagation process in concrete,and the number of cracks in concrete is large when the ITZ strength shows a U shape distribution.The decrease in ITZ strength value leads to a gradual increase in the number and range of cracks.When the ratio of the minimum bond strength of ITZ to the bond strength of mortar p<0.5,the concrete strength is significantly reduced and the cracks expand around the centre of the concrete model to form a network macro-crack,resulting in scattered fracture failure.When p>0.6,the cracks expand from the centre of the concrete specimen to the loading end to form a macroscopic penetration crack,resulting in block fracture failure.