High-Temperature Kiln Drying of Spruce Joists

It has been demonstrated that green eastern spruce joists can be successfully kiln-dried to 19 percent moisture content in less than 15 hours using a constant dry bulb temperature of 240?F. Further drying to an average moisture content of 12 percent required only about 23 hours compared to the present industrial practice which requires about 80 hours. A 15 percent dynamic transverse compression treatment prior to high-temperature drying gave no apparent reduction in total drying time but the overall value loss was significantly reduced. Based on mill-run proportions of pith, heart, and sap lumber, the respective degrade losses for drying to an average moisture content of 12 percent by conventional, high-temperature, and compression plus high-temperature drying systems were $2.61, $1.88 and $1.28 per Mbf. Results of static bending tests on 8-foot joists showed a reduction in MOE of 3.1 percent from the high-temperature drying and 4.0 percent from compression plus high-temperature drying. The MOR was reduced by 4.1 and 17.2 percent respectively. These reductions are substantially less than the inherent variability of randomly selected Construction grade joists; however, they can be detected in a research study by means of an appropriate analytical technique.

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