Experimental study of dynamic effects in moisture transfer in building materials

Abstract

In relation to moisture storage in porous materials, it is often assumed that the process dynamics do not affect the moisture retention. There is mounting evidence though that this notion is incorrect: various studies demonstrate that the moisture retention is influenced by the (de)saturation rates of the moisture transfer processes involved. The available evidence primarily stems from imbibition and drainage experiments on soils however, and compared to many other porous media, these tests consider rather permeable materials with relatively dominant liquid transport at comparatively large (de)saturation rates. The current knowledge may thus not be directly transferable to moisture transfer in porous media on the whole, and dedicated further research is required. This paper responds to that need, by reporting on an experimental investigation of the occurrence of dynamic effects on moisture transfer in building materials. Drying and ad-/desorption tests are executed on two building materials, in which moisture contents and moisture potentials are measured simultaneously. These are translated into dynamic retention relations and dynamic storage coefficients, which both distinctly demonstrate that moisture transfer in building materials, similar to moisture transfer in soils, is not free of dynamic effects. The findings imply that the widely accepted static theory for moisture storage in porous media is not generally valid and should be corrected for the occurrences of dynamic effects. Considering that such drying and ad-/desorption processes are dominant features in very many instances of moisture transfer in porous media, the repercussions of these findings may be large.

Hygrothermal effects and moisture kinetics in a bio-based multi-layered wall: Experimental and numerical studies

“…RH µ (11) This means that if µ 0 is modified by x%, the predicted ∆RH is modified by x.S% (at least in the range of µ 0 ±20%).…”

“…Note that heat and mass transfer phenomena have to be properly modeled and coupled, as highlighted in [5]: heat transfers in walls can have a significant effect on the hygric transfers and inversely. But despite the reliability of these models, it seems that inside some porous materials, and particularly in bio-based materials, simulations largely underestimate the time required for the water content to reach the equilibrium: this has been established for bio-based materials in [6,7,8] and by Reuge et al [9], but also for more traditional material such as cement compounds or concretes [10,11,12]. These considerations take on their full meaning in the cases of hygrothermal transfers with permanent fluctuations such as in materials of building envelopes, in soils or in food materials.…”

Reliability Study of Equilibrium Moisture Content Methods for Sorption/Desorption Isotherms Determination of Autoclaved Aerated Concrete

“…A round-robin test was performed within IEA/ECBCS 41 to determine the hygric properties of porous building materials in order to generate a data set for comparison of the numerical models [16]. As a result, recent studies experimented with quantification of the hygric properties from different aspects by applying different measurement techniques [17][18][19]. An important factor to consider is the specific technology and composition of the investigated porous material, which may differ significantly depending on the region as well as the manufacturer.…”

Development of The Experimental Stand With Centrally Located Specimen For The Investigation of Heat and Moisture Phenomena in Porous Building Materials

“…For this reason, the range of these air flow parameters influences the experimental stand development. For example, the experiment may be conducted in free convection conditions or with low velocity forced convection in a climatic chamber [1,10]. For high speed forced convection, special wind tunnels are built.…”