An Electrical Test for Decay in Wood

The study was made to see if the radio frequency electrical properties of wood could be used to detect the presence of decay. All wood samples came from two 6-foot logs, one of loblolly pine, Pinus taeda L., and one of American sweetgum, Liquidambar styraciflua L., called red gum in the trade. Quarter-sawed boards from these logs were kiln-dried to 6 percent moisture content and the sapwood portion cut in small beams 1/2-inch by 1/2-inch by 6 inches. The beams were brought to 7.7 percent moisture content, weighed, and the original ovendry weight calculated. For each fungus 56 beams were employed as decay samples. Four fungi, two brown rot and two white rot organisms were used. The brown rot and the white rot were used to decay the pine samples. The red gum samples were decayed by the brown rot organism and the white rot organism. Electrical measurements were all made at a frequency of 5 megacycles per second on a Boonton Q-meter model 160A. The conductivity of the wood bore a significant relationship to the amount of decay by the three fungi. Microscopic examination revealed abundant hyphae in the severely decayed wood, which may account for the increase in electrical conductivity. The dielectric constant was affected by decay only in the case of P. monticola. Moisture content had the greatest effect on the electrical properties.

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