Abstract
In this work, the transport equations of ionic species in concrete are studied. First, the equations at the porescale are considered, which are then averaged over a representative elementary volume. The so obtained transport equations at the macroscopic scale are thoroughly examined and each term is interpreted. Furthermore, it is shown that the tortuosity-connectivity does not slow the average speed of the ionic species down. The transport equations in the representative elementary volume are then compared with the equations obtained in an equivalent pore. Lastly, comparing Darcy’s law and the Hagen–Poiseuille equation in a cylindrical equivalent pore, the tortuosity-connectivity parameter is obtained for four different concretes. The proposed model provides very good results when compared with the experimentally obtained chloride profiles for two additional concretes.
Highlights
The tortuosity-connectivity for a fully saturated homogeneous material can be calculated from Equation (64) with r = R, where R is the radius of the saturated equivalent pore associated to a fully saturated representative elementary volume (REV): τ (r ) =
In order to obtain the transport equations at the macroscopic scale, the microscopic equations were integrated over the REV by means of the well known averaging technique
It was shown that the dispersion terms which arose from the averaging procedure can be ignored
Summary
The durability of concrete, which can be defined as its resistance to weathering action, chemical attacks and other degradation processes, is one of the most significant areas of research interest. Seeking to more practical approaches, in previous works, a constant tortuosity factor has been adopted which assumes that all the effects arising from pore orientation, connectivity, size variation, etc., can be encompassed by a mean value valid for all pore sizes [19,20,21] This is obviously a gross assumption since it depends on the implicit assumption that the effects of pore geometry and structure are the same for all pore sizes, even so, if the pore structure is characterized in detail, a sufficiently accurate aproach can be made. The equations at the porescale are considered, which are averaged over a representative elementary volume This procedure shows the origin of the tortuosity-connectivity parameter used for modelling ionic transport in porous media. This expression can be written as a function of the pore radii, or more conveniently, as a function of the pore water content
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