The fire resistance of cross-laminated timber (CLT) could be improved by treating the lamina with fire retardants. The major issues with this technology are the reduced bondability of the treated lamina with commercial adhesives. This study assessed several surface preparation methods that could improve the bondability and bond durability of fire-retardant treated wood with two commercial adhesives. Four surface preparation methods, including moisture/heat/pressure, surface planing, surface chemical treatment, and surface plasma treatment were assessed for their impact on the bondability and bond durability of lodgepole pine lamina. The block shear test results indicated that all surface preparation methods were somewhat effective in improving bond performance of fire-retardant treated wood compared to the untreated control wood samples, depending on the types of fire retardants and wood adhesives applied in the treatment process and bonding process. The selection of surface preparation, fire retardant, and wood adhesive should be considered interactively to obtain the best bond properties and fire performance. It may be possible to effectively bond the treated lamina with PUR adhesive without any additional surface preparation for the fire retardant used in the treatment at FPInnovations.
Glulam and laminated veneer lumber protected by a combination of treatment with borate by two processes, and a film-forming coating, were exposed outdoors in an above-ground field test using a modified post and rail test design. After eight years’ exposure, early to moderate decay was found in untreated test units, while those which were borate-treated by either method were generally sound up to six years and showed greatly reduced decay at eight years.
Glulam manufactured from laminating stock of three species pre-treated with ACQ-D or CA was exposed outdoors in an above-ground field test using a modified post and rail test design. After six years’ exposure, early to moderate decay was found in untreated test units, while those which were preservative-treated were completely sound.
Project contacts are Gerald Presley, Oregon State University, and Scott Noble, Kaiser+Path
Summary
The primary goal of this project is to enhance the durability of mass timber assemblies in high-moisture, high-termite risk regions. Only a few U.S. jurisdictions allow mass timber use by code adoption. Hawaii requires that all structural wood be treated to resist insects. Current topical or pressure treatments are allowed, but it is unclear how these treatments will perform in mass timber elements. Assembled cross-laminated timber (CLT) panels are too large to fit in pressure vessels. We will test the performance of individually treated wood members (lamella), assembled into CLT panels for compliance to structural requirements as well as resistance to termite attack in field trials. The resulting data will identify the most effective treatment options to protect CLT and other mass timber assemblies for use in Hawaii and similar regions with high termite exposure. The research implications will contribute to educating architects, engineers, builders and developers on modern timber construction in new regions.
