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Effects of deck washes and brighteners on the leaching of CCA components
1999 - IRG/WP 99-50128
Small CCA treated Southern pine decks were exposed to natural weathering and the CCA leaching characteristics determined by analyzing the collected rain drippage over several rain events. The decks were then treated with a number of commercial deck washes/brighteners and the CCA components in the wash solution compared to that from water wash only. Washes containing phosphoric acid, citric acid and oxalic acid resulted in relatively high copper losses during the washing treatment and slightly increased losses of the other components. Strong oxidizing agents such as sodium hypochlorite, resulted in oxidation of chromium to the hexavalent state and subsequent loss of soluble CrVI.
A Taylor, P A Cooper, Y T Ung

Effect of water repellents on leaching of CCA from treated fence and deck units - An update
1997 - IRG/WP 97-50086
In an earlier study, it was shown that CCA leaching losses could be reduced over an accelerated leaching and short term natural weathering exposures by post treatment application of a commercial water repellent. In this report, the effects of this coating and two commercial CCA solution water repellent additives are evaluated after two years of natural weathering. Wood boards were pressure treated with CCA or CCA + WR additives and assembled into deck or fence units. Some of the CCA only treated fence units were dried and brush coated with a commercial water repellent finish. After exposure to accelerated weathering, the units were installed out-of doors and the concentration of water drippage collected during rain storms analysed and compared. The water repellent formulation applied after treatment was most effective in reducing CCA component concentrations in the leachate and drippage samples. The water repellent additives incorporated in the CCA solution, had a positive, but lesser effect on the CCA component concentrations in the drippage from the fence units, but had no significant effect on the CCA leached from the deck units. Concentrations of copper in the water drippage from CCA treated decks and fences without water repellent dropped over the 2 year exposure, but arsenic and chromium levels did not drop significantly with time.
P A Cooper, Y T Ung, R M Vicar

Study of weathering Characteristics in Profiled and Treated Deck Boards
2014 - IRG/WP 14-40680
Wood exposed outdoors to repeated wetting and drying develops surface checks. Excessive checking of wooden deck boards has been a major source of dissatisfaction to consumers. In this study, Southern pine (Pinus sp.) deck boards were machined to flat (control) and ribbed surface profiles. The specimens were treated with aqueous formulations of 4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (EL2) and amine copper azole (CA-C) using a vacuum/pressure method. Boards were exposed to accelerated weathering for 576 h (24 days). The number, length and width of checks that developed in boards and average amount of cupping, twist and bowing in each test board were quantified after weathering. The results of statistical analysis showed all of the preservative-treated ribbed decking samples had a lower average number of checks compared to end matched flat samples. Checks were also shorter and narrower in the profiled deck boards than in the unprofiled specimens. Furthermore, the lowest amount of checking, cupping, twist and bowing was observed for specimens profiled and treated with the EL2.
M Akhtari, D Nicholas, L Sites

In-service performance of treated plywood bridge decks in Australia
2017 - IRG/WP 17-40794
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.
M A Powell

Long-term field exposure of wood-plastic composites processed on a commercial-size extruder
2020 - IRG/WP 20-40894
Wood-plastic composites (WPC) contain wood fiber (or flour), thermoplastics and additives and are exposed to UV light, moisture, and biological deterioration in outdoor installations. Accelerated laboratory tests can help to predict the durability of WPCs, but long term evaluations are needed to validate these results. Field exposed above-ground WPC deck boards (30.5 x 139.7 x 609.6 mm) and in-ground (19 x 19 x 457 mm) stakes were visually evaluated near Saucier, Mississippi and Madison, Wisconsin over 17 years. Four blends were extruded on commercial-scale equipment containing additives including colorant, light stabilizers, lubricant, and the fungicide zinc borate (ZnB). There are some difficulties evaluating the WPC materials compared to solid wood: in-ground stakes snap quite easily when removing them for inspection and decay is more difficult to determine because the WPC does not become soft. Differences in deterioration were seen between each test site: the in-ground deterioration was more severe in Mississippi and the above-ground deterioration was more severe in Wisconsin. The ZnB fungicide provided some decay protection in-ground even at the low level of 1%, and the UV stabilizer package (including colorant) slowed the color change compared to the WPC control above-ground. The blend including both ZnB and UV package provided both decay and UV protection, but mold and stain are still an issue for above-ground. The in-ground results are analogous to the short-term accelerated laboratory evaluations.
R E Ibach, C M Clemmons, N M Stark