Dynamic Compression Results in Greatly Increased Creosote Retention in Spruce Heartwood

Dynamic transverse compression treatment of green spruce heartwood joists, prior to pressure impregnation with coal-tar creosote, resulted in increased total retention and penetrated area. Three deformation levels were tested, and deformation to the 15 percent level, based on green joist thickness, was best. Total retention was increased by 62 percent (3.4 to 5.5 lb./cu.ft.) and penetrated area by 58 percent (20.8 to 32.8 percent of the cross section). An analysis of creosote retention in 5 consecutive 1/16-inch layers taken from the edge and face of each joist showed that the increases resulted mainly from substantially improved radial penetration on the wide face. At a radial depth of 3/16-inch the average retention in pre-stressed material was 6 lb./cu.ft. compared to only 1.9 lb./cu.ft. in controls. Slight increases in edge (tangential) penetration were not statistically significant. The effective, depth of preservative penetration on the wide face was increased by approximately 1/8 inch. Static bending tests indicated that, on a random basis, MOE and MOR of impregnated joists were not significantly reduced by the 15 percent compression treatment.

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