A discussion of “Analysis of the water absorption test to assess the intrinsic permeability of earthen materials”

Abstract

Abstract In February 2019, this journal published the article “Analysis of the water absorption test to assess the intrinsic permeability of earthen materials”. The author of this discussion considers the article’s simplification of moisture transfer in porous materials to a “competition between the kinetics of water ingress within the wall, which is driven by intrinsic permeability, and water evaporation, which is rather driven by resistance to vapour diffusion at the wall surfaces” in contradiction with the state-of-the-art on this topic. It is therefore reiterated that decades of research demonstrate the intrinsically unsaturated nature of moisture transfer in porous materials. The discussion continues by reviewing the article’s application of Kiessl’s/Kunzel’s exponential diffusivity. Whereas the article observes that this exponential diffusivity overestimates the capillary absorption, the theory on this formulation states that it should correctly reproduce the capillary absorption. It is furthermore noted that a similar application of the exponential diffusivity by one of the article’s authors in a related work contrarily results in an underestimation of the capillary absorption. These contradictions can only be explained by the faulty application of the exponential diffusivity by the article’s authors, rather than the exponential diffusivity being unsuited for earthen materials, as currently concluded in the article.