Effect of a two-stage heat treatment process on the mechanical properties of full construction timber

Abstract

This study investigated the impact of an industrially used two-stage heat-treatment method on the mechanical properties of full construction timber. Bending tests of full-size Norway spruce posts demonstrated changes due to heat treatment, such as a decrease in the density and bending strength, as well as an increase in the modulus of elasticity (MOE). The variability in bending strength and MOE appeared to be higher for treated posts and as a result the 5% values decreased, especially for the bending strength. The MOE was dependent on density for both treated and untreated posts, but this was not so for the bending strength. There appeared to be a relationship between the bending strength and the MOE, although it was rather weak, especially for treated posts. It was difficult to correlate the occurrence of natural defects in treated Norway spruce posts with an effect on the mechanical properties. Only a combination of several defects, such as large knots, enclosed pith and a deviating slope of grain, appeared to decrease the bending strength and MOE of treated posts, at least more than for untreated posts. The effect of a three year period of outdoor exposure on the strength properties of heat-treated terrace planking was limited. In particular, for the 5% value low strength range, where wood defects strongly determine the mechanical properties of wood, a three-year outdoor exposure did not change the bending strength or MOE of heat-treated wood

Microstructure, strength and structural integrity of heat-treated beech and spruce wood

“…Brischke et al, 2006Schuh, 2008), whereas the MOR of the weathered specimens decreased significantly. This impact of weathering stresses on static strength properties was also reported by Boonstra et al (2007) and Welzbacher et al (2011). Consequently, the decrease in RIM represents the decrease in structural integrity of the cell wall on a microlevel, whereas the decrease in MOR represents the combination of microstructural changes and (macro)impacts of cracks and other defects.…”

Influence of combined heat treatment and densification on mechanical properties of poplar wood

“…In the MOR values, all values except HTD33 increased by varying rates (26,72-55,29%) in HTD samples compared to the control sample. In contrast to these results, Boonstra et al (2007b) obtained a 6% reduction in bending strength, but a 17% increase on MOE in treated Norway spruce wood.…”

Effect of fungal exposure on the strength of thermally modified Norway spruce and Scots pine

“…In addition, Esteves et al (2007a) found 40% and 50% decreases in bending strength for pine and eucalypt wood, respectively, while the MOE was little affected. Reduced strength properties have also been reported by Kubojima et al (2000), Poncsák et al (2006), Sundqvist et al (2006), Boonstra et al (2007a), Esteves et al (2007b), Shi et al (2007) and Korkut et al (2008).…”