After Two Decades of Service . . . Glulam Timbers Show Good Performance

The purpose of this study was to establish whether glue joints made with resorcinol and phenol-resorcinol adhesives in laminated bridge timbers had the long-term durability that accelerated tests had indicated. The report describes the fabrication and treatment of the timbers and the condition of glue joints of 12 bridge installations ranging in service from 6 to 20 years. The principal accelerated tests were the standard block shear test (ASTM 905-49) and a cyclic delamination test (a forerunner of ASTM D 1101-59). Some timbers were glued and then treated with creosote, creosote-petroleum oil mixture, or pentachlorophenol in heavy oil. Other timbers were glued from lumber previously treated with waterborne fluorchrome arsenate phenol (FCAP) or creosote. The treated laminated timbers were generally in excellent condition with very little glue joint separation or checking. Timbers glued from creosote-treated lumber also were in very good condition after about 19 years of service. Timber glued from lumber treated with waterborne preservatives performed satisfactorily but seemed more susceptible to checking and delamination in areas with dry summer weather. It is suggested that the coating on the surface of timbers from oil-borne preservatives provides more protection against shrinking and swelling than waterborne preservatives. Indications of good durability from initial evaluation of glue joints for some of the earliest installations were confirmed by good performance in the timbers as well as by test results on samples from the timbers tested after 20 years’ exposure to the weather. No evidence of decay was observed in any of the treated timbers.

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