Darrel Nicholas

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.

The feasibility of applying an innovative process to manufacture composite decking boards with quartersawn or starsawn southern pine lumber bonded with phenol resorcinol formaldehyde (PRF) and polyurethane (PU) adhesives was studied. It was feasible to make quatersawn-based composite decking panels with possible improved surface qualities. Accelerated aging tests showed that composite quartersawn decking samples were more resistant to aging than flatsawn decking samples in terms of shear strength, especially after exposure to 12 wet–dry aging cycles. Compared with the PRF adhesive, the PU adhesive resulted in greater initial dry shear strength but had lower shear strength after the accelerated aging test. Furthermore, the amount of wood failure increased for the PRF-bonded samples and decreased for the PU-bonded samples after accelerated aging tests. Compared with solid quartersawn decking boards, the quartersawn composite decking boards had the same modulus of rupture and modulus of elasticity.

Summary: Two field test sites with different soil types were selected. Analysis showed that the two soils had considerable between-site variation in texture, base saturation, acidity, levels of metals, and cation exchange capacity. The sites also had moderate differences in average seasonal temperatures and rainfall. Stakes, made from defect-free southern yellow pine (SYP) sapwood and measuring 19×19×559mm, were treated to about 0.40 pcf (6.4 kg/m³) with chromated copper arsenate (CCA-type C). The stakes were installed at the two sites and sets of ten or more samples pulled after 55 and 66 months of exposure. The depletion of the individual components (chromium, copper and arsenic, oxide basis) from below-ground sections of each stake was then determined. No significant site effect on depletion was observed despite the large contrasts in chemical and physical properties between the two soils. Of the individual components, copper generally had the least depletion on a pcf weight loss basis while the greatest loss was observed with arsenic in three of the four time/site sets. The exposure times examined had no influence on depletion.

Methods of making wood decontaminable of major chemical warfare agents were investigated using phenol-formaldehyde and polyurethane resins. Selected phenol-formaldehyde resins impregnated in southern yellow pine gave enhanced dimensional stability and fire resistance properties without decreasing strength properties, but the decontaminability for one major chemical warfare agent was inadequate. Selected polyurethane resins impregnated in southern yellow pine gave enhanced dimensional stability and strength properties with only a minor deterioration in fire properties, and southern yellow pine, red oak, and aspen impregnated with these polyurethane resins were adequately decontaminated of all three major chemical warfare agents. A polyurethane resin that performs adequately as a coating material for this purpose was also identified.