Critical parameters on moisture dynamics in relation to time of wetness as factor in service life prediction

IRG/WP 14-20555

J Van Acker, I De Windt, W Li, J Van den Bulcke

The concept of natural durability or enhanced durability based on the presence of active ingredients having an impact on both fungi and insects is not the only parameter steering the material resistance. Complementary resistance to getting wet (wetting ability) and consequently the ease of drying afterwards will lead to a parameter related to the time a piece of wood will remain under such wet conditions that it is prone to decay. Since this concept is merely important for those conditions prone to wetting and drying focus for this complementary material resistance factor is mainly linked to use class 3 applications. This paper gives an overview of 52 wood species, 17 sets of modified wood and 8 wood based panels and the parameters derived from testing according to a protocol soon to become a European standard test method. The method is based on a complementary testing of on one hand floating specimens with a face on water with edges sealed and on the other hand a submersion test with open end grain cross sections. The dimensions are aligned with common field test specimens. Results showed that absorption and desorption figures after 24 hours could differentiate wood species but allowed to classify similar material in the same class. Based on curve fitting this approach can seemingly be improved and also parameters that explain better the water uptake rate and release rates next to total absorption and residual moisture content can be included. In the paper the data are presented using the unit g/m² for the floating test and kg/m³ for the submersion test but these values can easily be translated in percentages moisture content. Future data from continuous moisture measurements will allow underpinning the meaning of the critical parameters in relation to actual time of wetness.


Keywords: durability, material resistance, moisture dynamics, time of wetness, wetting ability

Conference: 14-05-11/15 St George, Utah, USA


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