Internal moisture content and temperature of standardized aboveground wood durability test specimens

Abstract

Durability of wood products intended for use in outdoor aboveground applications are evaluated using one or more standardized test methods. These methods use relatively small specimens in an effort to accelerate decay growth and allow detection of decay. In this study, we evaluated internal moisture content and temperature of standardized specimens and compared them with specimens of a simulated post and beam connection that is recommended for residential deck construction. Specimens of each type were cut from end-matched Southern Pine timbers and exposed above ground at a test site near Madison, Wisconsin. Pairs of stainless steel screws were inserted at multiple locations within each specimen to allow moisture content determination with a resistance-type moisture meter. Internal temperature was monitored in one specimen of each type using a thermistor probe and data logger. The specimens of the simulated post and beam connection sustained higher moisture contents and experienced less moisture content fluctuation than any of the standardized test specimens. Internal temperature also varied by specimen type but not to the extent observed for moisture content. The findings of this study suggest that frequent drying of standardized specimens has the potential to inhibit decay and may underestimate the decay hazard present within larger members of aboveground structures. Of the current standardized methods, the E18 ground proximity test appears to offer the best combination of relatively high moisture contents and ease of inspection. Other approaches, such as those that stack or layer groups of smaller specimens to entrap moisture and enhance decay, may warrant further consideration.