Multi-scale analytical theory of the diffusivity of concrete subjected to mechanical stress

• A multi-scale analytical method is built to predict the effect of mechanical stress on diffusivity.
• Porosity is treated as the main parameter influencing the diffusivity in concrete.
• The quantitative relation between volumetric strain and diffusivity is given.
• Good agreement between the theoretical results and the test data is obtained.
• Compressive stress decreases the diffusivity while tensile stress increases the diffusivity.

The diffusivity of concrete is closely related to the microstructure which involves the interfacial transition zone (ITZ) between aggregate particles and cement paste matrix at the meso-scale, as well as the microstructure of cement paste itself. At the micro-scale, the cement paste and the ITZ can be assumed to be composed of intrinsic cement paste phase and the pore-water inclusion, with different porosities. Under external mechanical stress, the porosities and the connectivity of capillary pores within the cement paste and the ITZ will be changed, resulting in the change of the chloride diffusivity of concrete. In this study, a multi-scale analytical model that can predict the chloride diffusivity of concrete subjected to mechanical stress is proposed. The quantitative relationship between the apparent diffusion coefficient of concrete and the mechanical stress (herein, i.e., the volumetric strain) as well as the current porosities of cement paste and the ITZ is evaluated. The main parameters in the analytical method are the capillary porosities of cement paste and the ITZ, the mechanical properties of the intrinsic cement paste phase and the aggregate, the volume fractions of aggregate and the ITZ, and the mechanical stress. The good agreement between the present theoretical results and the available test data illustrates the reliability and accuracy of the developed analytical approach.

Figure optionsDownload as PowerPoint slide