Cost effective extension of service life of bridge tie (sleepers) - Effectively applying borate during Boulton conditioning and treatment with copper naphthenate
J D Lloyd, T Chambers, J-W Kim
Current longevity of creosote treated wooden bridge ties in the South Eastern US is about 15 to 25 years, which is well below of the average service life of 33-50 years of railroad ties. Such short service life increases costs associated with maintenance of railroads including bridge down time for tie replacement as well as the cost for the new ties themselves. Because of this, many railroads are seeking non-wood alternative ties, even at vastly elevated initial cost. The objective of the study was to see if it is possible to apply borate as part of a dual treatment with copper naphthenate, in order to increase the service life of wooden bridge timbers at minimal additional cost.
Green hardwood ties were ported, borate treated, and then Boulton treated with copper naphthenate at a commercial tie treatment plant in Pennsylvania. Diffusion of borate within the wood appeared to be significantly enhanced by the elevated temperature and steam generated during the Boulton cycle and subsequent pressure treatment with copper naphthenate. The achieved retention and penetration of borate and copper naphthenate met AWPA standard retentions and AREMA guidelines. The longevity of ties should be significantly increased by protecting the heartwood with disodium octaborate tetrahydrate (DOT) and the sapwood with copper naphthenate. The results suggested that hardwood ties can be successfully treated with borate during a Boulton cycle and should allow the continued effective use of sustainable wooden bridge timbers.