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ABSTRACT
Wood-cement composites are one option for the recycling of spent chromated-copper-arsenate-(CCA) treated wood. This paper evaluates the effects of CCA-treated wood on selected properties of cement-bonded particleboard. CCA-treated wood is more compatible with Portland cement than untreated wood, resulting in boards with improved bending strength and stiffness, internal bond (IB) strength, and water absorption (WA), and thickness swelling (TS) performance. Incorporation of CCA-treated particles in a Portland cement matrix greatly reduced the leaching of copper and arsenic; however, chromium leaching was not reduced. Exposure of cement-bonded particleboards to decay fungi in a soil jar exposure indicated that untreated particles could undergo limited decay, while boards with CCA-treated particles were protected from deterioration. Generally, boards produced with higher water ratios and higher cement ratios had better physical and mechanical properties. For a given water/cement/wood ratio, boards produced at a density of 1.3 g/cm3 were of inferior quality compared to those produced at 1.2 g/cm3. Of the boards evaluated, those having a density of 1.2 g/cm3 and a cement/wood/water ratio of 1!0.33/0.6 produced the highest quality boards. All physical and mechanical properties could be modeled with multi-linear equations relating the above variables with a high degree of confidence.
Chromated copper arsenate (CCA) has been a commercial wood preservative treatment for more than 50 years, but during the past 20 years, its usage has grown dramatically (6,21). Thus, while the quantities of "spent" or out-of service CCA-treated wood generated each year is relatively low at this time, it is anticipated that significant levels of CCA-treated wood will be taken out of service within the next few decades. Residential construction materials such as decks, fences, and retaining walls will be a large component of this wood. It is estimated that approximately 2 million m' (70 million ft.') of CCA-treated wood will be taken out of service in Canada each yearby 2020, ofwhich more than 90 percent will be from residential construction (21). In the United States, approximately 10 million m' (350 million ft.') will be available (20). A recent study showed that CCA-treated wood in residential construction may have a shorter service life than previously assumed (13). This would result in accelerated production of spent treated wood.
At this time, viable options for dealing with spent CCA-treated...