Meso-scale Simulation of Influence of Frost Damage on Mechanical Properties of Concrete

Meso-scale constitutive models of frost-damaged concrete are developed in this study through numerical simulation using a two-dimensional Rigid Body Spring Model (RBSM). The aim of the simulation is to predict the macro behavior of frost-damaged concrete subjected to mechanical loading. The models also clarify the difference in failure behavior of concrete with and without frost damage. Zero strength elements and the concept of meso-scale plastic tensile strain are introduced into the normal RBSM springs to consider the experimentally observed cracking and plastic deformation caused by frost damage. The difference in the effect of frost damage on compression and tension behavior as found in the experiments is clearly predicted. Finally, analysis of notched beam subjected to bending after different degrees of frost damage is 1 Dr. Eng., Professor, Division of Built Environment, Graduate School of Engineering, Hokkaido University, Kita-ku, Kita 13, Nishi 8, Sapporo, Japan 060-8628, e-mail: ueda @eng.hokudai.ac.jp 2 PhD., Lecturer, Department of Civil Engineering, Faculty of Engineering, Syiah Kuala University, Darussalam, Banda Aceh 23111, Indonesia 3 Dr. Eng., Assistant Professor, Division of Civil Engineering, University of Tokyo, Bunkyo-ku, Hongo 7-3-1, Tokyo, Japan 113-8656 4 Dr. Eng., Associate Professor, Division of Built Environment, Graduate School of Engineering, Hokkaido University, Kita-ku, Kita 13, Nishi 8, Sapporo, Japan 060-8628 5 PhD., Associate Professor, State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China 2 carried out. The resulting load-deflection curves agree well with those obtained in experiments. These good correlations confirm the applicability of the meso-scale model for predicting the macro behavior of frost-damaged concrete. CE Database subject headings: Meso-scale Constitutive Model; Frost Damage; Rigid Body Spring Model (RBSM); Meso-scale Plastic Tensile Strain; Zero Strength Element (ZSE). Introduction The study of concrete at the meso-scale is useful for the precise evaluation of its characteristics, which are affected by the material characteristics of its components, such as mortar and aggregate, and their interfaces. Furthermore, deterioration in the material characteristics of concrete that has been damaged as a result of environmental action will, in future, be predicted through analysis at this scale (Wittmann 2004). Frost damage is one type of environmental deterioration that occurs in cold regions. Typical frost damage consists of surface scaling and internal micro-cracking caused by expansion of the materials (i.e. mortar). In recent years, there have been many studies on the mesoscopic modeling of concrete and concrete structures subjected to mechanical loading (Nagai et al. 2004; 2005; Stroeven and Stroeven 2001; Asai et al. 2003; Bazant et al. 2004). At the meso-scale, in which concrete is considered a composite material with three-phases (aggregates, mortar and interfacial transition 3 zones between them), Nagai et al. (2004; 2005) succeeded in simulating the failure mechanism and failure modes of mortar and concrete specimens using both twoand three-dimensional methods. By incorporating accurate meso-scale morphology, realized using an image-based geometry modeling technique, into a lattice-type numerical model, Asai et al. (2003) simulated the cracking behavior of concrete induced by meso-scale heterogeneities. Bazant et al. (2004) introduced a Confine-Shear Lattice Model (CSL model), in which the concrete meso-structure is simulated by a lattice connecting particles that represent the aggregate pieces. However, no meso-scale analysis of damaged concrete has previously been conducted. In this paper, analysis at the meso-scale of frost-damaged concrete subjected to mechanical loading is presented. The constitutive models used in the analysis are developed based on the plasticity and fracturing concepts. Moreover, the difference in failure behavior of concrete with and without frost damage is discussed. The analysis is carried out using a two-dimensional Rigid Body Spring Model (RBSM). RBSM is a discrete numerical analysis method first developed by Kawai (1977). The analytical model is divided into polyhedron elements whose boundaries are interconnected by two springs, called normal and shear springs, as shown in Fig. 1. Each element has two translational and one rotational degree of freedom at the center of gravity. A mesh arrangement of random geometry using a Voronoi diagram is used (Okabe at al. 2000) and a geometric computational program 4 developed by Sugihara (1998) is applied. Normal and shear elastic moduli are calculated by assuming a plane stress condition as follows (Nagai et al. 2004).