Detection of Re-Bar Corrosion in Re-inforced Concrete Structures Using Modal Analysis
A current need for industry, the Federal Highway Administration, and many other safety related agencies is the ability to access the structural integrity of existing steel reinforced concrete structures. This includes roads, bridges, runways, dams, water towers, containment basins, buildings, retaining walls etc. The method for analysis must be simple, non-intrusive, quick and inexpensive. It must be able to detect both early stage and advanced corrosion to facilitate timely repair or replacement.
The Johns Hopkins Applied Physics Laboratory (JHUAPL) has developed and successfully field-tested a non-destructive corrosion identification system using modal analysis. An audio speaker operating between 500 and 10K HZ is clamped to a concrete structure. Amplified acoustic waves penetrate the structure interacting with the buried re-bar and setting up flexural and torsional vibration within each re-bar. The resulting amplitude and frequency are sensed and recorded. A modal analysis is performed on site by the computer which shows that well bonded re-bar has low amplitude and unbonded (corroded) re-bar has higher amplitude. APL has repackaged the field-mounted hardware into a small, user-friendly and lightweight configuration, which can be used for testing by bridge inspectors to validate it against current inspection methods.
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