Heat-treatment of spruce (Picea abies) and pine (Pinus sylvestris) beams (45 x 145 mm) gave a reduction in bending strength of approximately 50%. The bending stiffness (modulus of elasticity) only decreased by 3.5%. Tests were carried out according to EN 408. Another effect of the heat-treatment was increased variation in bending strength. The 5th percentile value of the bending strength, the so called characteristic value, decreased by 66% for spruce and by 55% for pine after heat-treatment. The study consisted of 200 spruce beams and 200 pine beams of Swedish origin. Half of the material was heat-treated and the other half was used as controls. The heat-treatment was carried out in a steam chamber in Finland at a maximum temperature of 220°C. The level of treatment was assumed suitable for above ground end uses. When storing the material in a climate that was approximately 20°C/65% relative humidity the heat-treated material reached an equilibrium moisture content of 3-3.5%. For the untreated material corresponding figure was 12-12.5%. The dry density for the heat-treated material decreased by approximately 7.5% compared to the untreated material.

Download document (321 kb)
free for the members of IRG. Available if purchased.

Purchase this document