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Water movement in building walls: interfaces influence on the moisture flux

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Abstract

Most building elements are a composite of different material layers; however the majority of the works presented in literature were developed for multi-layered elements with perfect contact interface, without resistance. Experimental results presented in literature showed that a considerable hydraulic resistance could be created by the imperfect contact between two porous building materials. Moisture transport in multi-layered building elements can deviate from the moisture transport found for the combination of the single material elements, so the assumption of perfect hydraulic contact could lead to significant errors in predicting the moisture transport. This work presents an experimental campaign and a critical analysis of water absorption in samples of two different building materials (clay brick and autoclaved aerated concrete) with and without joints at different positions (heights) and different contact configurations (natural contact and air space between layers). The results show that when the moisture reaches the interface there is a slowing of the wetting process due to the interfaces hygric resistance. The interfaces hygric resistance, in the AAC samples, is only observed for the joint located from a distance of 2 cm of the wetting plane. The penetration coefficient of the two building materials analysed is very different. Finally, the evolution of the distribution of liquid in the porous medium was analysed in terms of the Boltzmann transform method and anomalous diffusion equation.

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Abbreviations

A :

Contact area (m2)

A W :

Water absorption coefficient (kg/m2s0.5)

B :

Water penetration coefficient (m/s0.5)

D W :

Moisture diffusion coefficient (m2/s)

h :

Penetration depth (m)

m t :

Weight of the specimen after time t (kg)

m 0 :

Initial mass of the specimen (kg)

M t :

Total amount in time t (kg/m2)

n :

Real number (-)

P c1 :

Suction pressure of material 1 (Pa)

P c2 :

Suction pressure of material 2 (Pa)

q :

Moisture flow across the interface (kg/m2s)

Q max :

Maximum transport flow (kg/m2s)

R :

Hygric resistance (m/s)

t :

Time (s)

x :

Axial-coordinate (m)

w :

Volumetric moisture concentration (kg/m3)

w 0 :

Initial volumetric moisture concentration (kg/m3)

w ∞ :

Equilibrium volumetric moisture concentration (kg/m3)

α :

Variable given by \( \alpha = 1/(n + 1) \) (−)

η :

Boltzmann variable (m/s0.5)

η* :

Similarity variable, \( \eta * = x/t^{\alpha } \) (m/sα)

ρ :

Density (kg/m3)

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Acknowledgments

The research work presented herein was supported by FEDER funds through the Operational Programme for Competitiveness Factors—COMPETE and by national funds through the FCT—Portuguese Foundation for Science and Technology, under research project. J.M.P.Q. Delgado would like to thank FCT for financial support through the Grant SFRH/BPD/84377/2012.

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Authors and Affiliations

  1. CONSTRUCT-LFC, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, s/n, 4200-465, Porto, Portugal

    J. M. P. Q. Delgado, V. P. de Freitas & A. S. Guimarães

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  1. J. M. P. Q. Delgado
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  2. V. P. de Freitas
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  3. A. S. Guimarães
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Correspondence to J. M. P. Q. Delgado.

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Delgado, J.M.P.Q., de Freitas, V.P. & Guimarães, A.S. Water movement in building walls: interfaces influence on the moisture flux. Heat Mass Transfer 52, 2415–2422 (2016). https://doi.org/10.1007/s00231-016-1755-z

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