Thesis
Evaluating the feasibility of thermally modified western hemlock, Douglas-fir, and western larch implemented in cross laminated timber
Washington State University
Master of Science (MS), Washington State University
12/2019
DOI:
https://doi.org/10.7273/000003984
Handle:
https://hdl.handle.net/2376/125140
Abstract
Cross laminated timber (CLT) is an emerging technology in the North American market but is susceptible to degradation if exposed to long-term moisture. Decay risk is typically mitigated through preservative chemical treatment but cannot be applied to CLT because the thin shell of preservative would be planed off in refractory species. Thermal modification (TM) is a promising sustainable alternative which increases the wood's durability and dimensional stability at the expense of generally reduced mechanical properties. Unlike preservative chemical treatment, thermal modification fully penetrates the depth of the lumber and could provide a solution to increasing the durability of CLT. Unfortunately, understanding of the effects of the TM process on a range of mechanical properties and bondability is limited and no readily available research has been conducted on TM specifically for CLT applications. This study aims to investigate the viability of TM CLT by testing properties of matched pairs of specimens from western hemlock (WH), Douglas-fir (DF), and western larch (WL) in the following: small clear bending, specific gravity, screw withdrawal, dowel bearing, delamination propensity, block shear, and rolling shear. Most mechanical properties were reduced from thermal modification with the WH degrading the least and WL degrading the most. Two exceptions were a slight increase in TM WH bending stiffness by 5.7% and an increase in dowel bearing strength parallel to grain in TM WH and TM DF. The remaining mechanical properties were degraded by varying degrees depending on test and species. The specific gravity was not found to be statistically different after thermal modification, but the equivalent moisture content decreased by over 40% post-treatment. Delamination and wood failure were adequate and comparable to control specimens, indicating a good bond can be developed between TM wood. Using the shear analogy method, apparent out-of-plane bending of a TM WH panel would increase by 3.5%-5.3% depending on span/depth, whereas the DF/WL would decrease by 20%-23%. Generally, WH had the least degradation in the tested properties and could provide a viable option for TM CLT with the DF and WL needing further refinement in the treatment process to mitigate mechanical property degradation.
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Details
- Title
- Evaluating the feasibility of thermally modified western hemlock, Douglas-fir, and western larch implemented in cross laminated timber
- Creators
- Johnson William Jones
- Contributors
- DONALD A BENDER (Advisor) - Washington State University, Composite Materials and Engineering Center
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Civil and Environmental Engineering
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Identifiers
- 99900890799001842
- Language
- English
- Resource Type
- Thesis