Investigation of Grading Methods of Recycled Australian Hardwood for Structural Purposes
Year: 2024
Type: dissertation
Abstract: In Australia, strict environmental legislation combined with an escalating demand for sustainable hardwood in construction projects is placing significant pressure on hardwood resources. Concurrently, a substantial amount of demolition timber, an underutilized resource, is being discarded into landfills. This thesis explores the potential for structural reuse of demolition hardwood, addressing the critical need for sustainable practices in the construction industry.\n\nThe current state of scientific knowledge includes the "Interim Industry Standard Recycled Timber - Visually Stress Graded Recycled Timber for Structural Purposes" for recycled timber grading, which, despite its introduction, has not been widely adopted and is utilized by only a few companies. Additionally, non-destructive testing (NDT) methods have been developed but remain untested for recycled timber in commercial settings.\n\nThe primary aim of this research was to assess recycled Australian hardwood and reliably grade its quality. The methodology used involves the SMART THUMPER™ smartphone app, which applies the resonance method to determine the dynamic modulus of elasticity (MoEdyn), thereby estimating the static modulus of elasticity (MoE). The "Interim Industry Standard" was used for visually grading recycled timber to determine a reliable MoE and modulus of rupture (MoR). Afterwards, information gathered from both methods was compared to estimate material properties reliably.\n\nThe procedure involves visually strength grading 20 recycled Australian hardwood boards with dimensions between 1100 mm and 1500 mm in length and a cross-section of approximately 50 mm x 150 mm using the "Interim Industry Standard". The boards were cut into smaller specimens, visually graded a second time, and then subjected to destructive testing in a four-point bending experiment to determine their MoR and MoE.\n\nThe study shows that the SMART THUMPER™ app and therefore MoEdyn provides a reliable estimate of MoE for recycled boards, with only a 15% underestimation. However, they do not provide sufficient information on MoR. On the other hand, the "Interim Industry Standard" provides a solid basis for estimating MoR, although it significantly underestimates MoE by up to 32%. The "Interim Industry Standard" has a high rejection rate for boards with small imperfections, even when they possess substantial strength properties. This suggests that the standard requires more than two recycling grades and further detailing. Accurate estimations of both MoR and MoE can be achieved by combining both methods. \n\nFuture research is recommended to develop an automated grading procedure that incorporates automated visual grading with camera systems and resonance methods like SMART THUMPER™. This approach requires a significant amount of data to establish a connection between visual characteristics and material properties of recycled wood. It also requires a reproducible grading system that can be used on-site by untrained staff. This will pave the way for more efficient and sustainable recycling of timber in the construction industry.
Authors: Bay, Yannik, Technische Universität München
Language: English
Subfield: Building and Construction
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6982684037