Abstract
Treated wood timbers employed in ground contact are often installed with a cement collar to firmly fix the structural wood post in place. Few prior studies have determined the effect of concrete on decay efficacy on treated wood, however. Treated wood nominal 4 × 4 posts were installed at four locations, with the upper ground-contact portion of each post encased in concrete, and the samples removed at various times for pH measurements. The wood alkalinity quickly increased at all four sites for the portion of the treated wood in concrete contact compared to the wood in ground contact without concrete. In laboratory decay tests employing three decay fungi, untreated wood which was first exposed or unexposed to concrete had no consistent difference in decay susceptibility. For wood treated with three different commercial copper/organic systems, cement exposure had no effect on wood treated with an amine copper azole system, while treatment with amine copper quat showed a statistically significant fungal efficacy enhancement for cement-exposed samples with both copper-tolerant fungi. Conversely, with a micronized copper azole preservative, cement exposure resulted in reduced fungal efficacy compared to treated samples which were not cement-exposed for all three decay fungi.
Highlights
Treated wood products are often used as posts in ground contact to support decks and various other structures
Four 12-foot nominal 4 × 4 southern pine (Pinus spp.) posts commercially treated with micronized copper azole (MCA) with a labeled retention of 2.4 kg/m3 were obtained from a local lumber dealer in Starkville, Mississippi (MS)
Commercial MCA-treated ground-contact posts surrounded by a concrete collar installed at four outdoor sites quickly increased to a greater pH than the lower portion of the post below the concrete at all four test sites locations
Summary
Treated wood products are often used as posts in ground contact to support decks and various other structures. Cement is often applied around the posts It is unknown what effect the alkaline cement, which contains high levels of alkaline calcium compounds that would increase the pH of the wood, has on the efficacy of the treated wood against brown-rot decay fungi. If the cement does increase the susceptibility of treated wood to decay, it could reduce the service life of the posts and pose serious issues due to early collapse of structures and resulting injuries. Another study evaluated the effect of CaCl2 on decay of untreated wood and copper-citrate-treated wood when exposed to S. lacrymans in a soil block test [5]. Another study reported that sapwood pine samples in soil block decay tests with 2% CaCl2 added to the soil significantly reduced the extent of decay by both Gloeophyllum trabeum and Rhodonia placenta [6]
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