The demolition sector generates a large amount of timber waste that could be directly reused or recycled in other products for structural purposes. Timber should be graded before it is used for structural purposes, and visual strength grading standards designed for new timber do not properly grade recovered timber. Cross Laminated Timber (CLT) is now one of the most common wood products used in construction. CLT would therefore be a good option for recycling timber due to the high quantity of material used in CLT manufacturing. This paper investigates the possibilities of using recovered timber from demolition to manufacture CLT. Twelve CLT panels from recovered and new timber were manufactured and tested. The static modulus of elasticity was found to be the same between recovered and new timber, while the bending strength of CLT from recovered timber was lower than it was for CLT from new timber. Non-destructive testing for the estimation of mechanical properties of boards and CLT panels was successfully developed.
The modulus of elasticity and bending strength of 45 structural Salzmann pine timber pieces with nominal dimensions of 150x200x5400 mm3 from an existing 18th century structure were estimated by semi-destructive density estimation probing method (drilling chips extraction) and acoustic wave velocity (stress and ultrasound wave). Bending strength, modulus of elasticity and density were obtained according to the EN 408 European standard, and visual grading singularities were recorded. Visual grading methods are highly ineffective for existing timber structures. Sample mechanical properties show a typical profile of material from existing structures, and this was compared with the results of similar works. MOE and MOR predictive models were proposed with determination coefficients r2 of 66–68% and 51–52%, respectively, using dynamic MOE, relative edge knot diameter and slope of grain as independent variables. MOR prediction improved when these grading parameters were included.