Development of preservative treatment recommendations for red oak and red maple glued-laminated timber bridge members

Creosote pressure-treating cycle guidelines and a post-conditioning treatment were developed to obtain satisfactory penetration (12.7 mm or 0.5 in. minimum) and retention (192.2 kg/m³ or 12.0 pcf minimum) of creosote and to minimize in-service creosote bleeding in red oak and red maple glued-laminated timbers. The proposed creosote-treating cycle was based on a preliminary study and was used to treat a red oak glued-laminated timber bridge. A retention of 192.2 kg/m³ (12.0 pcf) of creosote was obtained with penetration of more than 12.7 mm (0.5 in.). The treating cycle guidelines were slightly modified and used to treat a red maple glued-laminated timber bridge. Penetration ranged from 50.8 mm (2.0 in.) to completely through the cross section of the laminated beams with retention exceeding 240.3 kg/m³ (15.0 pcf). Treatment of red maple bridge material also used a newly developed low-temperature/vacuum, post-creosote treatment cycle. The modified cycle resulted in an excellent creosote treatment of the red maple glued-laminated timber bridge and the post-treatment was successful in cleaning the surfaces and in controlling bleeding of the preservative.