13th International Conference on Fracture June 16–21, 2013, Beijing, China 1 Numerical Modeling on the Stress-Strain Response and Fracture of Modeled Recycled Aggregate Concrete Wengui Li1,2, Jianzhuang Xiao1,*, David J. Corr2, Surendra P. Shah2 1 Department of Building Engineering, Tongji University, Shanghai 200092, China 2 Center for Advanced Cement-Based Materials, Northwestern University, Evanston 60208, USA * Corresponding author: jzx@tongji.edu.cn Abstract According to the nanoindentation tests, the constitutive relationship of the Interfacial Transition Zones (ITZs) in Recycled Aggregate Concrete (RAC) is proposed with a plastic-damage constitutive model. Based on the meso/micro-scale constitutive relations of mortar matrix, numerical studies were undertaken on Modeled Recycled Aggregate Concrete (MRAC) under uniaxial loadings to predict mechanical behavior, particularly the stress-strain response. The tensile stress tends to concentrate in the ITZs region, which leads to the development of microcracks. After the calibration and validation with experimental results, the effects of the mechanical properties of ITZs and new mortar matrix on the stress-strain response and fracture of MRAC were analyzed. The FEM modeling is capable of simulating the complete stress-strain relationship of MRAC, as well as the overall fracture pattern. It reveals that the mechanical properties of new mortar matrix and the corresponding new ITZ play a significant role in the overall stress-strain response and fracture process of MRAC. Keywords Modeled recycled aggregate concrete (MRAC), Interfacial transition zones (ITZs), Plastic-damage constitutive model, Stress-strain response, Fracture 1. Introduction Most of cement-based materials have intrinsic heterogeneous and nonlinear mechanical behaviors due to the random distribution of multiple phases over the nano-, micro-, meso- and macro-scales [1-4]. A better understanding of mechanical properties including the failure processes by both experiments and computer modeling has become one of the most critical research topics for concrete [5-7]. Corr et al. predicted the mechanical properties of concrete in tension with the consideration of meso-scale randomness in the cohesive interface properties [8]. Cusatis et al. formulated the Lattice Discrete Particle Model (LDPM) and simulated experiments include uniaxial and multiaxial compression, tensile fracture, shear strength, and cyclic compression tests [9, 10]. Moreover, concrete was simulated with plasticity-damage constitutive model, and showed a very good correlation with the experimental results [11]. With the emergence of nanoindentation technique, it is available to experimentally measure the properties of the ITZ (Interfacial Transition Zone) between aggregate and mortar matrix [12, 13]. Due to the recent advances in understanding the microstructure, thickness, and mechanical properties of the ITZ and the developments of computational methods, the micromechanical behavior of concrete can be effectively simulated to get a deeper insight into the effect of each phase (such as aggregate size and shape, ITZ thickness and micromechanical properties, and the mortar matrix mechanical properties, etc.). In this study, Modeled Recycled Aggregate Concrete (MRAC) is a volume element of RAC which is used to simplify the real RAC study. A plastic-damage model is adopted within FEM analysis. The mechanical properties of ITZs in MRAC are obtained by a nanoindentation technique. Two-dimensional microscale numerical modeling is conducted in order to investigate the effects of ITZs on the overall behavior and failure process of MRAC under both uniaxial loadings.
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