Condition of Chromated Copper Arsenate Treated Hem-Fir Guardrail Posts after 20 Years in Service in Western Washington State

Abstract

Wood guardrail posts are among the most common wood materials currently used in highway construction. Preservative treated hem-fir is an important species for guardrail applications in the western United States. The service life of treated timber post guardrail systems has been estimated to be between 10 and 20 years. However, there is surprisingly little information on performance of timber guardrails. One aspect of the estimate of service life is wood durability. This study assessed the flexural properties, level of decay, and residual preservative levels in chromated copper arsenate preservative treated hem-fir guardrail posts removed from a project near Bellingham, Washington. Increment cores were removed from each post to assess preservative treatment and fungal colonization. The posts were tested for flexure properties in a three-point bending test. Posts that met the American Wood Protection Association standards for preservative penetration tended to have lower levels of internal decay after 20 years in service, and all but six posts retained sufficient flexural properties to meet AASHTO standards.