Movement of borate from liquid borate inserts in dual-treated bridge timbers

ABSTRACT

Creosote-treated wooden bridge ties in the South-Eastern U.S.A. last about 15–20 years, which falls well below the national average of 40 years for crossties. It was demonstrated that diffusion of inserted liquid disodium octaborate tetrahydrate within wooden bridge ties was dramatically increased during Boulton treatment. The objective of this study was to determine how much diffusion of borate inside the bridge tie occurred over time, after initial treatment. Green hardwood bridge ties were ported, borate treated and then Boulton treated with copper naphthenate at a commercial tie treatment plant. Retention and location of borate within the wood was tested at 3, 14 and 40 weeks after the treatment. As previously found, movement of borate within the wood was significantly enhanced by the elevated temperature and steam generated during the Boulton cycle. 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. It is hoped that the results will reduce environmental impact, improve safety and enable railroads to continue to use wood with confidence.

KEYWORDS:

• Borate
• bridge timbers
• copper naphthenate
• DOT
• dual treatment
• sleepers
• ties

Acknowledgements

The authors would like to acknowledge the help and support of Mellott Wood Preserving during this research.

Disclosure statement

No potential conflict of interest was reported by the authors.