Multiscale modeling of interactive diffusion processes in concrete

Deterioration of concrete is governed by coupled diffusion processes such a s heat conduction, moisture transfer, and chloride ion penetration. The dif fusion processes can be characterized by multiscale modeling. At the macros copic level, a thermodynamic approach is used in the present study as a fra mework to derive coupled diffusion equations and constitutive equations. In the case of hygrothermal coupling, it is found that there are additional c oupling effects in the stress-strain relationships aside from the conventio nal thermal expansion and drying shrinkage. At the mesoscopic level, compos ite theories are used to develop the material models between effective tran sport properties (macroscopic) and transport properties of constituents (me soscopic). The results shows that, even for noncoupled processes, the effec tive properties are not simply the volumetric average over the constituent phases. An analytical multiscale prediction model for chloride diffusion is developed based on an assumption that both chloride diffusivity and bindin g capacity are independent of free chloride concentration. The analytical s olution is used as an example to compare with available test results, showi ng that the model is quite accurate for regular concrete cured 28 days or l onger, The multiscale model can accurately predict the effect of mesoscopic parameters (e.g., aggregate content) and microscopic parameters (e.g., wat er-to-cement ratio) on chloride penetration.