Prediction is based on a one-dimensional finite difference solution
of Fick's second law of diffusion, with a variable external chloride
concentration and a two-layer representation of the concrete.
Month Ext. chloride Temperature (oC)
Total duration of exposure days
Unexposed boundary condition is
Constant at zero
Reflecting boundary (no chloride escape)
Member thickness m
Depth of Reinforcement mm
Degree of hydration
Volume fraction of aggregate %
Air content %
Initial chloride concentration of concrete g chloride/g cement Guidance
Click here to view database of
concrete diffusivities from literature.
Note that all diffusion coefficients are apparent diffusivity values, as we
are modelling transport in the pore space of the concrete based on Fick's
Time dependent diffusion coefficient for bulk concrete takes the form of
Be sure that you use values of m in the range (0,1).
Reference: Mangat and Molloy, Materials and Structures, Vol. 27,
338-346, 1994. Note- Mangat and Molloy found m values ranging from
0.44 to 0.86 and also that approximately:
To have a constant D value with time, simply set Dinf to this desired value
and Di to zero
Dinf m*m/s at 25 C
Curing time before exposure of concrete to chlorides days
The surface layer of the concrete may have a different (lower or higher) D
value than the bulk concrete due to carbonation or poor curing practices.
Input the surface layer D value relative to the bulk D value and the
thickness of this layer. To bypass
this feature, set the skin layer thickness to 0.0 or use D(surface concrete)/
Ratio D (surface concrete)/D (bulk concrete)
Thickness of surface layer mm
Activation Energy for diffusion kJ/mole
Based on a Langmuir isotherm of the form:
where C(bound) is in (mole Cl-)/kg cement and
C(free) is in (mole Cl-)/L
Rate constant for binding s-1
Assuming the formation of Freidel's salt from all of the
C3A and C4AF initially available in the cement powder.
C4AF content of cement % on a mass basis
Rate constant for aluminate reactions with chloride s-1
Time at which surface treatment is applied days
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