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The use of laminated veneer lumber (LVL) has steadily increased over the last two decades and is now found in numerous applications. The early application of this material was primarily for flange stock in the manufacture of I-joist assemblies and as a component in parallel chord or Warren truss systems (4). Today, its use has grown to be best classified as a major construction material for a diverse array of structural and semi-structural applications. Newer uses and experimental applications of LVL include headers, scaffold planks, concrete forms, utility pole and cross arms, truckbed decking, door rail and stiles, window frames and doorjambs, fascia/trim board, kiln-stickers, stair components, ladder stock, boat hull stringers, and furniture framework, etc. One particular application of interest that stimulated this study was the potential of LVL material as a subcomponent in hardwood glued laminated (glulam) timber bridge systems being developed for the Pennsylvania Department of Transportation (PennDOT). Research conducted with a red oak Press-Lam demonstration project has shown the technical feasibility of using LVL materials for timber bridge applications (9).
One important aspect in the use of LVL materials for timber bridge applications is proper preservative treatment. LVL materials for utility pole applications have been treated with oilborne pentachlorophenol and on a less common trial basis with waterborne chromated copper arsenate (CCA). Unfortunately, pentachlorophenol treatment is often not available without significant cost for transportation to the nearest treating facility. At present, creosote treatments have been selected as the principal preservative in the PennDOT standard specifications for hardwood glulam timber bridges. Waterborne CCA and other metal salt treatments were not recommended due to questionable penetration of the preservative and chemical fixation in the cell wall of hardwoods (3).
Research conducted with red maple and yellow-poplar glulam timbers has indicated that adequate preservative penetration at 12 pcf creosote retention is possible to comply with the requirements of American Wood-Preservers' Association (AWPA) C14--Wood for Highway Construction--Preservative Treatment by Pressure Processes (3). However, the researchers noted that preservative penetration was quite variable for yellow-poplar glulam timbers, depending on the occurrence of less permeable heartwood. Yellow-poplar, not unlike Douglas-fir, is known to be a difficult-to-treat or refractory species. Review of the literature reveals only limited data describing the creosote preservative treatment characteristics (retention and penetration) for...