Use of Acoustic Assessment to Detect Decay and Assess Condition of Wooden Guardrail Posts

Abstract Wood guardrail posts are the most common wood materials currently used in highway construction. Maintenance crews and engineers are often faced with the challenge of rapidly assessing the extent of decay or damage in individual posts. Many conventional intrusive techniques are unsuitable for inspecting guardrail posts because they are too time-consuming. Acoustic detection could be an ideal inspection method because of its rapid assessment. The potential for using acoustic inspection for wooden guardrail posts was assessed on treated hem-fir guardrail posts removed from western Washington State. The posts were tested nondestructively using an impulse hammer, and then increment cores were removed from each post for assessing preservative treatment and fungal colonization. The posts were then tested to failure in bending to determine flexural properties. All but one of the posts met the minimum threshold for strength according to the American Association of State Highway and Transportation Officials. There was a weak correlation between acoustically predicted modulus of elasticity (MOE) and actual MOE. Correlations between acoustically predicted MOE and modulus of rupture were slightly better but still weak and lower than would be acceptable for this method to be used in the field. The results indicate that acoustic methods might be useful for detecting the presence of advanced decay but failed to provide definitive estimates of post properties.