Grading of recovered Norway spruce (Picea abies) timber for structural purposes

An increasing amount of timber is recovered from demolition and can be value-added through reuse or recycling for structural applications. This study investigates the possibilities of using visual and non-destructive parameters to estimate the mechanical properties of recovered timber so that it can be graded for new applications. A batch of nineteen recovered Norway spruce (Picea abies (L.) Karst.) rafters was studied. The application of two visual grading standards produced a rejection of 95% of the specimens. Estimation of modulus of elasticity was per-formed using ultrasound and vibration NDT techniques, with determination coefficients (R2) of 0.66 and 0.75 respectively. In the case of bending strength estimation, R2 were 0.60 and 0.77 respectively. Visual knottiness parameter was only a statistically significant variable in the estimation model of local modulus of elasticity. Density was estimated using drilling chips extraction and drilling penetration resistance with R2 of 0.66 and 0.58 respectively.