Prediction of elastic modulus and Poisson's ratio for unsaturated concrete

Many concrete structures are located in water environment, but the underwater concrete is usually unsaturated even though it has been soaked in the water for a very long time. Some experiments have proven that the mechanical properties of concrete are affected by the saturation degree of fluid and aspect ratio of pores. Several publications discussed the saturated concrete qualitatively, but few gave quantitative analysis especially for the unsaturated concrete. In terms of the microstructure of unsaturated concrete, equivalent medium and inclusion-based theory of composite materials, a model is proposed to explain the changes happened in the wet concrete and to predict the elastic parameters (including elastic modulus and Poisson's ratio) of unsaturated concrete. The viscosity of water in pores, micro-cracks and the further hydration of cement are taken into account in this paper by means of the definition of saturation concept according to the effect of pore water on the modulus of concrete. In this model, both stiff effect of water and soft effect of cracks on the concrete are introduced to describe the bulk modulus, at the same time the effect of shear rate on the shear modulus is considered. The comparison between the theoretical models and experimental results in the extreme state indicates that the model proposed in this paper is valid to predict the elastic properties of unsaturated concrete. (c) 2006 Elsevier Ltd. All rights reserved.