Nebraska LTAP


Date of this Version


Document Type



Pashoutani, S. and Zhu, J. (2019). Condition Assessment of Bridge Decks with Asphalt Overlays. NDOT Research Report SPR-P1(17) MO65.


Ground penetrating RADAR (GPR) is a widely used nondestructive testing (NDT) method for bridge deck evaluation. However, the current GPR signal and data processing software and algorithms are not able to provide comprehensive information about bridge deck condition. Although the original objective of this research project was to develop GPR analysis algorithms for condition assessment of bridge decks with asphalt overlay, the scope of work has been expanded to concrete bridge decks with or without overlays.

In this study, the research team developed a complete GPR analysis procedure that includes the following components: 1) obtain zero-time for GPR reflection at the deck surface; 2) extract the electromagnetic wave velocity in the cover depth (from surface to top reinforcement mat) using migration method;3) identify rebar positions using automated rebar picking algorithm; 4) extract migrated amplitude at each rebar location; 5) calculate rebar depth using the extracted velocities for all rebars; 6) normalize rebar reflection amplitude and further correct the amplitude using rebar depth. These analyses will provide the following images of bridge deck: surface deterioration condition, cover thickness, velocity in cover concrete (and asphalt overlay), and attenuation. Comparing the amplitude correction methods based on travel time, the proposed depth correction method provides more accurate evaluation of bridge deck deterioration conditions. The developed GPR analysis algorithms have been validated on bridge decks with different types of overlays.