Chromated Copper Arsenate Preservative Treatment of North American Hardwoods. Part 2. CCA Leaching Performance

Abstract

Summary Seven North American hardwood species were vacuum or vacuum/pressure treated with 2% CCA-C solution and fixed at temperatures of 21°C and 50°C under conditions of high relative humidity (95%). The rates of fixation results are presented in Part 1 of this study. Red maple (Acer rubrum L.), red oak (Quercus rubra L.), American beech (Fagus grandifolia Ehrh), white birch (Betula papyrifera Marsh.), trembling aspen (Populus tremuloides Michx.), basswood (Tilia americana L.) and yellow poplar (Liriodendron tulipifera L.) were evaluated. The softwood red pine (Pinus resinosa Ait.) was included for comparison. Adequately fixed wood blocks (99.9% chromium reduction) were exposed to leaching by the AWPA E11 procedure. All CCA components were leached in high quantities from oak wood, while from red maple and beech, high arsenic leaching occurred. Leaching losses from aspen, basswood and yellow poplar were low and comparable for both fixation temperatures. In most species, the amount of leaching was affected by the treating method, with lower leaching from pressure treated wood blocks than from vacuum treated blocks. Removal of extractives from maple and oak blocks before treatment affected the CCA leaching performance in these species. Extracted red oak had lower chromium and copper leaching, but higher arsenic leaching. In contrast, extracted red maple had reduced leaching of all CCA components compared to unextracted wood. The examined hardwoods can be classified into three groups according to their CCA fixing and leaching characteristics: fast fixing/high leaching group (beech, red oak and red maple), intermediate fixation rate and leaching group (white birch and red pine) and slow fixing and low leaching group (aspen, yellow poplar and basswood).