Salt crystallisation at the surface of a heterogeneous porous medium

INPT, UPS, IMFT (Institut de Mécanique des Fluides de Toulouse), Université de Toulouse - Allée Camille Soula, F-31400 Toulouse, France, EU and CNRS, IMFT - F-31400 Toulouse, France, EU

^a mprat@imft.fr

Received: 7 February 2012
Accepted: 16 April 2012

Abstract

Evaporation of saline solutions from a porous medium often leads to the precipitation of salt at the surface of the porous medium. It is commonly observed that the crystallized salt does not form everywhere at the porous medium surface but only at some specific locations. To explain this phenomenon, we consider efflorescence formation at the surface of a saturated heterogeneous porous column (finer porous medium in coarse porous medium background) in the wicking situation. We study the impact of permeability and porosity contrasts on the efflorescence formation location from a simple visualisation experiment and Darcy's scale numerical simulations. We show that the porosity is the most sensitive parameter for our experiment and that efflorescence forms at the surface of the medium of lower porosity. A simple efflorescence growth model is then used to explain why the efflorescence continues to grow at the surface of the lower porosity medium without spreading over the adjacent surface of the greater porosity medium.