Using emissivity-corrected thermal maps to locate deep structural defects in concrete bridge decks

Nancy DelGrande; Philip F. Durbin

doi:10.1117/12.209770

19 May 1995 Using emissivity-corrected thermal maps to locate deep structural defects in concrete bridge decks

Nancy DelGrande, Philip F. Durbin

Proceedings Volume 2456, Nondestructive Evaluation of Aging Bridges and Highways; (1995) https://doi.org/10.1117/12.209770
Event: Nondestructive Evaluation of Aging Infrastructure, 1995, Oakland, CA, United States

Abstract

Dual-band infrared (DBIR) thermal imaging is a promising, noncontact, nondestructive evaluation tool to evaluate the amount of deteriorated concrete on asphalt-covered bridge decks. We conducted proof-of-principle demonstrations to characterize defects in concrete structures which could be detected with DBIR thermal imaging. We constructed two identical concrete slabs with synthetic delaminations, e.g., 1.8-in. thick styrofoam squares, implanted just above the 2-in. deep steel reinforcement bars. We covered one of the slabs with a 2-in. layer of asphalt. We mounted the DBIR cameras on a tower platform, to simulate the optics needed to conduct bridge-deck inspections from a moving vehicle. We detected 4-in. implants embedded in concrete and 9-in. implants embedded in asphalt-cevered concrete. The midday (above ambient) and predawn (below ambient) delamination-site temperatures correlated with the implant sizes. Using DBIR image ratios, we enhanced thermal-constrast and removed emissivity-noise, e.g., from concrete compositional variations and clutter. Using the LLNL/VIEW code, we removed the asphalt thermal-gradient mask to depict the 4-in. deep, 9- in. square, concrete implant site. We plan to image bridge deck defects from a moving vehicle for accurate estimations of the amount of deteriorated concrete impairing the deck integrity. Potential longterm benefits are affordable and reliable rehabilitation for asphalt-covered decks.

Citation Download Citation

Nancy DelGrande and Philip F. Durbin "Using emissivity-corrected thermal maps to locate deep structural defects in concrete bridge decks", Proc. SPIE 2456, Nondestructive Evaluation of Aging Bridges and Highways, (19 May 1995); https://doi.org/10.1117/12.209770

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