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Relationship Between the Formation Factor and the Diffusion Coefficient of Porous Materials Saturated With Concentrated Electrolytes: Theoretical and Experimental Considerations.

Relationship Between the Formation Factor and the
Diffusion Coefficient of Porous Materials Saturated With
Concentrated Electrolytes: Theoretical and Experimental
Considerations.
(1140 K)

Snyder, K. A.

Concrete Science and Engienering, Vol. 3, No. 12,
216-224, December 2001.

### Keywords:

porous materials; diffusion; concretes; porous media;
transport; formation factor

### Abstract:

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It has been proposed previously that the formation
factor, in conjunction with the self-diffusion
coefficient, can be used to determine the apparent
diffusion coefficient. Strictly speaking,this
application is incorrect. The formation factor is equal
to the ratio of the self-diffusion coefficient to the
microstructural diffusion coefficient, which is a
quantity that characterizes the pore structure and is
independent of the pore solution electro-chemistry. The
origin of this relationship will be shown using both the
electro-diffusion transport equation and the definition
of the formation factor. In practice, service life
models that solve the electro-diffusion transport
equation as a function of time require the formation
factor in order to calculate the microstructural
diffusion coefficient: the effects of the pore solution
chemistry are then calculated independently. A method is
needed to estimate the formation factor from either
diffusion or conductivity data so that service life
models can be applied to a particular material. An
experiment on a model porous material is used to
demonstrate one method for determining the formation
factor from divided cell diffusion data. The estimated
formation factor is then compared to results from
conductivity measurements. Differences among the
self-diffusion coefficients of the various diffusing
species accentuates the difference between the
microstructural and the apparent diffusion coefficients.
The significance of this result to cementitious systems
is discussed.
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