Coupled Creep and Damage Model for Concrete at Moderate Temperatures

Abstract

We develop in this study a coupled creep-damage model for concrete subjected to moderate temperatures. The coupling procedure relies on the concept of pseudo-strains introduced by Schapery [1], which allows to reformulate the initial viscoelastic problem as an equivalent elastic one by using a correspondence principle. The creep model is based on a micromechanical approach where a simplified representation of the material as a composite made of a linear viscoelastic matrix with distributed elastic inclusions and pores is adopted. One interesting feature is that analytical expressions for both bulk and shear moduli in the time space are derived in simpler cases when a limited number of Maxwell elements are involved to describe the matrix behavior. The well-known macroscopic isotropic damage model due to Mazars [2] is adopted to reproduce the cracking effects. The evolution of the damage variable is governed by an equivalent strain calculated from the pseudo-strains. The model is further extended to the case of moderate temperature increases with the aid of the equivalent time method. It is then applied to the simulation of concrete basic creep tests at different temperatures ranging from 20 to 80°C. The results are compared to experimental data and show a good agreement provided an adequate identification of the model parameters. The model response tends to show that the creep strains result mainly from the viscous characteristics of the material, and to a lesser extent to the damage growth. This conclusion holds for both ambient and moderate temperatures.