Abstract
Thermally modified wood is becoming commercially available in North America for use in outdoor applications. While there have been many studies on how thermal modification affects the dimensional stability, water vapor sorption, and biodeterioration of wood, little is known about whether thermally modified wood is corrosive to metal fasteners and hangers used to hold these members in place. As thermally modified wood is used in outdoor applications, it has the potential to become wet which may lead to corrosion of embedded fasteners. Here, we examine the corrosiveness of thermally modified ash and oak in an exposure test where stainless steel, hot-dip galvanized steel, and carbon steel nails are driven into wood and exposed to a nearly 100% relative humidity environment at 27 °C for one year. The corrosion rates were compared against control specimens of untreated and preservative-treated southern pine. Stainless steel fasteners did not corrode in any specimens regardless of the treatment. The thermal modification increased the corrosiveness of the ash and oak, however, an oil treatment that is commonly applied by the manufacturer to the wood after the heat treatment reduced the corrosiveness. The carbon steel fasteners exhibited higher corrosion rates in the thermally modified hardwoods than in the preservative-treated pine control. Corrosion rates of galvanized fasteners in the hardwoods were much lower than carbon steel fasteners. These data can be used to design for corrosion when building with thermally modified wood, and highlight differences between corrosion of metals embedded in wood products.
Highlights
Wood is a sustainable biomaterial that has been used as a building material since the beginning of civilizations
In all but one case, the corrosion rates were less than 0.3 μm year−1 and the standard deviations were bigger than the mean corrosion rate
This is in line with previous results that have shown that stainless steel fasteners exhibit little to no corrosion in preservative-treated and untreated softwoods [34]
Summary
Wood is a sustainable biomaterial that has been used as a building material since the beginning of civilizations. Preservative treatments protect wood by impregnating it with chemicals that are either fungistatic or fungitoxic and inhibit fungal growth. In contrast to preservative-treated wood, the decay resistance in modified wood is a result of non-toxic changes to the wood structure which make the wood harder for the fungi to colonize. Modified wood is a modification process where the wood properties are changed by heating wood in a non-oxidizing environment. Given that thermally modified wood has improved decay resistance and moisture properties, there is interest in using it in place of preservative-treated wood in certain outdoor environments. The corrosion of metal fasteners has been widely studied since a 2004 change in the registration of wood preservatives in the United States [5]. In addition to providing new properties of thermally modified wood, the experiments provide valuable information on the corrosivity of hardwood species, of which little data exists
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