In-service performance of treated plywood bridge decks in Australia
M A Powell
Engineered wood products have a long history of use in bridge construction in Australia. The first bridges incorporating chemically protected engineered wood components were installed in the 1850’s and some survive to this day. Preservative treated plywood bridge deck panels have been employed since the 1980’s as a replacement for the more traditional hardwood plank decks. This paper reports on the condition of engineered wood bridge deck panels through an examination of core samples cut from preservative treated plywood decks after up to 20 years’ in-service. The panels had been manufactured using either; copper chrome arsenic (CCA) preservative in an envelope treatment process or an alkaline copper quaternary (ACQ) preservative in a veneer treatment process. The in-service performance of both types of panels is discussed in relation to results from preservative penetration and retention testing together with a consideration of the severity of the termite and decay hazards to which they were exposed. All but one deck panel were found to be sound, unaffected by decay, the exception was a panel that had been adequately treated but came from a location where it appeared that poor design or detailing had increased the decay hazard. This proven long term satisfactory performance of both envelope and veneer treated plywood panels in what is a particularly hazardous above-ground end-use suggests that current penetration requirements are appropriate for this product category.
Keywords: veneer, envelope, penetration, bridge, deck, service life