Method of meshing ITZ structure in 3D meso-level finite element analysis for concrete

Meso-level finite element analysis (FEA) is a popular way to study the influences of meso-level structure of concrete (namely the aggregate, the mortar and the Interfacial Transitional Zone (ITZ) structures) on the macro-level properties. However, it’s been a huge challenge to mesh the ITZ structure in concrete because of the unique layer structure of ITZ, which is 10–50µm thick and rather small compared to the normal sizes of coarse aggregates. If ITZ were meshed by hexahedral elements or tetrahedral elements which were 10–50μm in all three dimensions, millions of ITZ elements would be generated and it’s impossible to perform FEA on such a huge concrete model. In the current meso-level FEA in the literature, ITZ is either represented by zero-thick interface elements or over-thick elements, either of which is far from the real dimension of ITZ, leading to big discrepancies between the numerical results and experimental results. In this paper a method to generate ITZ meshes called aggregate-expansion method (AEM) is proposed to generate wedge elements around 50µm thick to represent ITZ’s layer structure. The total number of generated ITZ meshes is limited and acceptable in meso-level FEA for concrete. A digital concrete specimen is generated from CT images with ITZ meshes generated by AEM and effects of ITZ on the compressive stress/strain/displacement distributions of concrete were studied. The characteristics of stress–strain response of the digital concrete specimen under tension were also studied and compared with experimental data. •Aggregate-expansion method is proposed to generate realistic meshes for ITZ in concrete.•50µm thick wedge meshes generated by AEM are close to ITZ’s real thickness.•Total number of ITZ meshes generated by AEM is small and acceptable in FEA.•Effects of ITZ on stress/strain/displacement distribution of concrete are studied.•Tensile stress–strain response of concrete is predicted and validated with experiments.