Preservative treated wooden bridge ties in the South Eastern USA have a service life of about 15 to 20 years, which falls well below the average service life of 40 years of railroad cross ties (sleepers). It has been shown that cross tie life is significantly extended using borate dual treatment and this is now commercialized in bridge timbers using borate inserts. In previous research, it was demonstrated that distribution of disodium octaborate tetrahydrate (DOT) within the wooden bridge ties was dramatically accelerated during Boulton treatment. The objective of this study was to determine how much diffusion of borate inside the bridge tie after initial treatment occurred over time. Green hardwood bridge ties were ported, borate treated, and then Boulton seasoned and treated with copper naphthenate at a commercial tie treatment plant in Pennsylvania, U.S.A. Retention and location of borate within the wood was tested at 3, 14 and 40 weeks after the treatment. It appeared that borate continued to diffuse inside of the tie and would likely treat and protect a significant volume of the heartwood over time and thus increase bridge tie life in a similar way to crossties.

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