Modeling Drying Shrinkage in Reconstructed Porous Materials: Application to Porous Vycor Glass.
Modeling Drying Shrinkage in Reconstructed Porous
Materials: Application to Porous Vycor Glass.
Bentz, D. P.; Garboczi, E. J.; Quenard, D. A.
Modelling and Simulation in Materials Science and
Engineering, Vol. 6, 211-236, 1998.
porous materials; porous media; capillary condensation;
computer models; drying shrinklage; microstructure;
A three-dimensional representation of the microstructure
of porous Vycor glass was generated from a transmission
electron micrograph, and was analysed to compute the
locations of all capillary-condensed water as a function
of relative humidity. On solid surfaces where
capillary-condensed water was not present, an adsorbed
water layer, whose thickness is a function of relative
humidity, was placed. As a function of relative
humidity, fixed pressures were specified in all
capillary-condensed water, and the change in specific
surface free energy with relative humidity was taken
into account for the adsorbed water layers. New
finite-element codes were developed to determine the
drying shrinkage, in response to the changes in the
specific surface free energy of the adsorbed water
layers and to the fixed pressures in the capillary
condensed water. Existing finite-element and
finite-difference codes were used to evaluate the
elastic moduli, the electrical and thermal conductivity,
and the fluid permeability of the material. Bulk
properties such as fluid permeability and electrical and
thermal conductivity agreed well with experiment. By
adjusting the elastic moduli of the solid backbone,
which are not experimentally determined quantities, the
computed porous glass elastic moduli, and computed low
and high relative humidity shrinkage all agreed well
with experimental values. At intermediate relative
humidities, the agreement for shrinkage was worse,
partly due to inaccuracies in the simulated water
desorption curve, and partly due to the fact that
water-induced swelling of the solid backbone, an effect
that is probably present in the real material, was not
taken into account in the model computations.