Conference, Proceedings

( ) i n
Φ − Φ
K i = ki
i i,
crit
where: ni =1+FDmi, FDmi is the mean fractal dimension of the component volume, ki is the
transport parameter of the component, i is the component volume, i,crit is the critical volume
of the component needed for a connected network to be formed through the material, the term
i i,crit is the relevant volume portion considered.
The critical volume is also known as the critical threshold volume for connectivity percolation.
The critical volume value is specific for particular transport processes. The volume participates
on the transport only if some critical minimum part of the volume is present. If i,crit, the
component volume portion or the pore volume fraction is not percolated in the material
volume. In such a case it is necessary to take into consideration the serial interconnection of the
component volume with other components.
The exponent ni expresses the deviations of real pores from parallel components model, their
regularity.
At equilibrium material moisture contents corresponding to the environment with the relative
humidity higher than ca 97 %, the capillary condensation is dominant. The equilibrium
moisture content corresponding to these and higher humidities is dependent on the capillary
pressure and is expressed by retention curve. The capillary pressure value is proportional
inversely to the radius of the largest capillaries filled with water and it is expressed by Laplace
equation:
p
c
⋅σ
w = −
r
2
where w is the surface tension of water.
Mois ture content (m3/m3)
1,0
0,8
0,6
0,4
0,2
0,0
1,E +00 1,E +01 1,E +02 1,E +03 1,E +04 1,E +05 1,E +06
Pore radius (nm)
Figure 2: Moisture adsorption curve modelled from MIP results
(3)
(4)
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