This is a specific model for nonlinear moisture transport in isotropic cementitious
materials, based on .
The governing equation
Isotropic material for moisture transport based on Bazant
and Najjar - BazantNajjarMoisture
is a special case of Eq. (237), valid under
the assumption that the slope of the sorption isotherm is linear, i.e. the
moisture capacity is constant.
In Eq. (235), is the relative humidity and is the
humidity-dependent diffusivity approximated by
where is the diffusivity at saturation (typical value for concrete
mmday), is the dimensionless ratio of
diffusivity at low humidity to diffusivity at saturation (typical
), is the humidity ``in the middle'' of the
transition between low and high diffusivity (typical value
), and is dimensionless
exponent (high values of , e.g. 12, lead to a rapid transition
between low and high diffusivity). Optionally, it is possible to
specify the moisture capacity. This property is not needed for solution
of the diffusion equation (235),
but it is needed if the computed change of relative humidity is transformed
into water content loss (mass of lost water per unit volume).
The model parameters are summarized in Tab. 54.
Nonlinear isotropic material for moisture transport - summary.
||Nonlinear isotropic material for moisture transport
||BazantNajjarMoistureMat num(in) #
d(rn) # c1(rn) # n(rn) #
alpha0(rn) # hc(rn) # [ capa(rn) #]
||- num material model number
||- d material density
||- c1 moisture diffusivity at full saturation [m s]
||- n exponent [-]
||- alpha0 ratio between minimum and maximum diffusivity [-]
||- hc relative humidity at which the diffusivity is exactly
between its minimum and maximum value [-]
||- capa moisture capacity (default value is 1.0)