Acoustic emission monitoring of early corrosion in prestressed concrete piles

Prestressed concrete (PC) piles in marine environments are vulnerable to corrosion damage especially at their tidal zone because of the concurrent exposure of steel reinforcement to moisture, chlorides, and oxygen. Early detection of corrosion in prestressed strands is desirable to enable the effective planning and prioritizing of maintenance operations. This paper reports on experiments aimed at testing the hypothesis that acoustic emission (AE) monitoring is suitable to recognize and classify early corrosion damage in PC piles exposed to saltwater. In fact, AE is sensitive to the formation and growth of microcracks in both steel and concrete, which may develop upon depassivation of reinforcement and buildup of corrosion by-products. In addition, the influence of AE signals produced through flexural cracks in the concrete is of less concern for PC piles as such cracks are seldom produced under service loads. Five specimens representative of full-scale portions of PC piles were designed to accelerate corrosion and subjected for 1year to wet/dry cycles in saltwater simulating tidal action. The specimens were monitored continuously with AE sensors. Benchmark electrochemical measurements were routinely performed to understand when depassivation of the steel strands occurred. Visual evidence of early corrosion was collected from strands removed from two decommissioned specimens. It is shown that AE intensity analysis is more effective than AE signal strength and cumulative signal strength analysis in recognizing corrosion damage. Intensity analysis-based criteria for the assessment of early corrosion damage are proposed, complementing previously developed criteria for more severe corrosion damage in steel strands. Copyright (c) 2014 John Wiley & Sons, Ltd.