MULTISCALE MODELING OF INTERACTIVE DIFFUSION PROCESSES IN CONCRETE

Deterioration of concrete is governed by coupled diffusion processes such as heat conduction, moisture transfer, and chloride ion penetration. The diffusion processes can be characterized by multiscale modeling. At the macroscopic level, a thermodynamic approach is used in the present study as a framework to derive coupled diffusion equations and constitutive equations. In the case of hygrothermal coupling, it is found that there are additional coupling effects in the stress-strain relationships aside from the conventional thermal expansion and drying shrinkage. At the mesoscopic level, composite theories are used to develop the material models between effective transport properties (macroscopic) and transport properties of constituents (mesoscopic). The result shows that, even for noncoupled processes, the effective 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 binding capacity are independent of free chloride concentration. The analytical solution is used as an example to compare with available tests results, showing that the model is quite accurate for regular concrete cured 28 days or longer. The multiscale model can accurately predict the effect of mesoscopic parameters (e.g., aggregate content) and microscopic parameters (e.g., water-to-cement ratio)on chloride penetration.

[1]  Hsueh-Chia Chang,et al.  MULTI-SCALE ANALYSIS OF EFFECTIVE TRANSPORT IN PERIODIC HETEROGENEOUS MEDIA , 1982 .

[2]  G. R. Jerauld,et al.  The effect of pore-structure on hysteresis in relative permeability and capillary pressure: Pore-level modeling , 1990 .

[3]  John Saliba,et al.  Transient moisture transport in a cracked porous medium , 1993 .

[4]  Jacky Mazars,et al.  Thermohygrometric and mechanical behaviour of concrete using damage models , 1997 .

[5]  Yunping Xi,et al.  A model for moisture capacities of composite materials Part I: formulation , 1995 .

[6]  Olivier Coussy,et al.  Modeling of Thermochemomechanical Couplings of Concrete at Early Ages , 1995 .

[7]  Y. Xi.  A model for moisture capacities of composite materials Part II: application to concrete , 1995 .

[8]  Muhammad Sahimi,et al.  On the improvement of the effective-medium approximation to the percolation conductivity problem , 1984 .

[9]  Yunping Xi,et al.  Moisture diffusion in cementitious materials Moisture capacity and diffusivity , 1994 .

[10]  Laurent Molez,et al.  Damage mechanics of concrete structures subjected to mechanical and environmental actions , 1998 .

[11]  Sven Thelandersson,et al.  On the multiaxial behaviour of concrete exposed to high temperature , 1983 .

[12]  Z. Bažant,et al.  Moisture diffusion in cementitious materials Adsorption isotherms , 1994 .

[13]  Zvi Hashin,et al.  Effective thermal expansion coefficients and specific heats of composite materials , 1970 .

[14]  Yunping Xi,et al.  Shrinkage of cement paste and concrete modelled by a multiscale effective homogeneous theory , 1997 .

[15]  Z. Bažant,et al.  Drying creep of concrete: constitutive model and new experiments separating its mechanisms , 1994 .

[16]  Zdeněk P. Bažant,et al.  Mathematical modeling of creep and shrinkage of concrete , 1988 .

[17]  Z. Bažant,et al.  Modeling Chloride Penetration in Saturated Concrete , 1999 .

[18]  A. Bensoussan,et al.  Asymptotic analysis for periodic structures , 1979 .

[19]  Invasion and transport processes in multiscale model structures for porous media , 1994 .

[20]  A. E. Sáez,et al.  The effective homogeneous behavior of heterogeneous porous media , 1989 .

[21]  P. King.  The use of renormalization for calculating effective permeability , 1989 .

[22]  Gilles Pijaudier-Cabot,et al.  CONTINUUM DAMAGE THEORY - APPLICATION TO CONCRETE , 1989 .