# Prediction of a Chloride Ion Penetration Profile for a Concrete

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.

## Please supply the following parameters (defaults provided)

### Environmental Parameters

Specify external chloride concentration and temperature as a function of month of the year:

```  Month     Ext. chloride      Temperature (oC)
conc. (moles/liter)

January

February

March

April

May

June

July

August

September

October

November

December

```
Beginning month of exposure is:

Total duration of exposure days

Unexposed boundary condition is

### Structural Design Parameters

Member thickness m

Depth of Reinforcement mm

### Concrete Mixture Parameters

w/c ratio

Degree of hydration

Volume fraction of aggregate %

Air content %

Initial chloride concentration of concrete g chloride/g cement Guidance

### Diffusion Coefficients (D)

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 2nd law.

Time dependent diffusion coefficient for bulk concrete takes the form of D=Dinf+Di*t-m

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:

m=2.5(w/c)-0.6

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

Di m*m/s

m

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)/ D(bulk concrete)=1.0.

Ratio D (surface concrete)/D (bulk concrete)

Thickness of surface layer mm

Activation Energy for diffusion kJ/mole

### Chloride Binding Parameters Guidance

```Based on a Langmuir isotherm of the form:
C(bound)=(alpha*C(free))/(1.+beta*C(free))

where C(bound) is in (mole Cl-)/kg cement and
C(free) is in (mole Cl-)/L
```

Alpha

Beta

Rate constant for binding s-1

### Chloride Reaction Parameters Guidance

```Assuming the formation of Freidel's salt from all of the
C3A and C4AF initially available in the cement powder.
```
C3A content of cement % on a mass basis

C4AF content of cement % on a mass basis

Rate constant for aluminate reactions with chloride s-1

## New Feature (March 2006)

### Set this time to a time greater than the total exposure time to turn off this feature

Time at which surface treatment is applied days

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