Demonstration of dual-band infrared thermal imaging for bridge inspection. Phase II, final report [report]

P.F. Durbin, N.K. Del Grande, P.C. Schaich
1996 unpublished
DBIR Bridge Inspection repoltmFwHA page ii I EXECUTIVE SUMMARY Developing and implementing methods of effective bridge rehabilitation is a major issue for the Federal Highway Administration (FHWA). The nation spends $5 billion annually to replace, rehabilitate or construct new bridges. According to the National Bridge Inventory, over 100,OOO U.S. bridges are structurally deficient. About 40,000 of these bridges have advanced deck deterioration. The most common cause of serious deck
more » ... s deck deterioration is delamination Delaminations result when steel reinforcements within the bridge deck corrode, creating gaps that separate the concrete into layers. A reliable inspection technology, capable of identifying delaminations, would represent a powerful new tool in bridge maintenance. To date, most bridge inspections rely on human interpretation of surface visual features or chain dragging. These methods are slow, disruptive, unreliable and raise serious safety concern. Infixed thermal imaging detects subsurface delaminations and surface clutter, which is introduced by foreign material on the roadway. Typically, foreign material which is not always evident on a video tape image, produces a unique IR reflectance background unlike the thermal response of a subsurface delamination. Lawrence Livermore National Laboratory (LLNL) uses dual-band infrared (DBIR) thermal imaging to identify and remove nonthermal IR reflectance backgrounds from foreign material on the roadway. DBXR methods improve the performance of IR thermal imaging by a factor of ten, compared to single-band infrared (SBXR) methods. DBIR thermal imaging allows precise temperature measurement to reliably locate bridge deck delaminations and remove wavelength-dependent emissivity variations due to foreign material on the roadway. .. We conducted a two-phase study to develop and demonstrate DBIR imaging for bridge deck inspection. The first phase demonstrated the DBIR method on a surrogate bridge deck containing synthetic delaminations. The second phase demonstrated the DBIR method at the Grass Valley Creek Bridges near Redding CA. We designed and fielded a mobile DBIR bridge inspection laboratory and drove this self-contained unit at limited highway speeds over 0.4 lane miles of bridge deck We demonstrated the power of DBIR thermal ima@g by removing the bridge deck clutter, which had unique spatial, spectral, thermal, thermal inertia, emissivity and temporal responses, unlike the IR responses which characterize bridge deck delaminations. The LLNL precise thermal imaging method provides an enabling technology for rapid, reliable, bridge deck inspections while minimizing fane closures. The LL;?TL method can indicate the fractional area of the bridge that is delaminated as well as locate and characterize the damaged regions. This technique is expected to help prioritize bridges for repair and then to direct the repairs to specific locations. DBIR Bridge Inspection report to FWHA Lawrence Livermore National Laboratory conducted a feasibiliw study to demonstrate the applicability of DBIR imaging to bridge decks. We constructed surrogate bridge decks of concrete slabs with steel reinforcements for the proof-of-principle demonstration. Using a tower platform, we measured the DBIR system response to temperature and emissivity differences between normal, cluttered, and defective areas of the surrogate bridge decks. The statement of work for Phase I is included in Appendix A.
doi:10.2172/419070 fatcat:h2prg2bd6bdd7lrsyyowl44cwi