13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Size Effect Analysis of Recycled Concrete Fracture based on Micromechanics Using the Base Force Element Method Yijiang Peng 1,*, Nana Dang 1, Lijuan Zhang 1, Jiwei Pu 1 1 Department of Civil Engineering, Beijing University of Technology, Beijing 100124, China * Corresponding author: pengyijiang@bjut.edu.cn Abstract In this paper, the base force element method (BFEM) on damage mechanics is used to analyze the fracture properties of recycled aggregate concrete (RAC) on meso-level. The recycled aggregate concrete is taken as five-phase composites consisting of natural coarse aggregate, new mortar, new interfacial transition zone( ITZ) , old mortar and old ITZ on meso-level. The random aggregate model is used to simulate the meso-structure of recycled aggregate concrete. The size effects of mechanics properties of RAC under uniaxial tension loading are simulated using the BFEM on damage mechanics. The simulation results agree with the test results. This analysis method is the new way for investigating fracture mechanism and numerical simulation of mechanical properties for recycled aggregate concrete. Keywords Base force element method (BFEM), Micromechanics, Fracture property, Size effect, Recycled aggregate concrete (RAC) 1. Introduction Concrete is considered as heterogeneous composites which mechanical performance is much related with the microstructure of material. The mechanical performance is usually obtained using experimental method. However, testing usually consumes a large amount of manpower and material resources, and test results are usually more discrete. In order to overcome this defect, the concept of numerical concrete was presented by Wittanmm et al (1984) based on micro-mechanics. Subsequently, some scholars did some creative works in this field, and made a number of models. Among them, the two important models are the lattice model and the random aggregate model. For example, Schlangen et al (1992, 1997) applied the lattice model to simulate the failure mechanism of concrete. Liu et al (1996) adopted the random aggregate model to simulate cracking process of concrete using FEM. Peng et al (2001) adopted the random aggregate model to simulate the mechanics properties of rolled compacted concrete on meso-level using FEM. Du et al (2008) simulated the failure mechanism of beam under impact loading and triangular cyclic loading by using displacement-controlled FEM, stress-strain curves and dynamic bending strengths of specimens. Recycled concrete material which is used as a green building material has attracted more and more researchers with the shortage of resources and an increasing number of construction wastes. They have carried out series of experiments and some conclusions have been reached. An overview of study on recycled aggregate concrete has been given by Xiao et al (2012). However, because of the complexity of recycled coarse aggregates, conclusions made by different researchers are usually not very accordant, even opposite sometimes. To remove effects of experimental conditions, some numerical researches on meso-level was considered. For example, numerical simulation on stress-strain curve of recycled concrete was taken by Xiao et al (2009) with Lattice Model under uniaxial compression. A method on meso-mechanics analysis was proposed by Peng et al (2011) using FEM for recycled aggregate concrete based on random aggregate model. However, the Numerical researches on the damage mechanism for recycled concrete material have just begun. In recent years, a new type of finite element method - the Base Force Element Method (BFEM) has been developed by Peng et al (2006-2012) based on the concept of the base forces by Gao (2003). In this paper, the BFEM on potential energy principle is used to analyze recycled aggregate concrete (RAC) on meso-level. The size effects of mechanics properties of recycled aggregate
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