1. Coupling GPR and IR Thermography to Detect Damage in Reinforced Concrete Bridge Decks
Dr. Nicole Martino, Roger Williams University
Mike Sock, RIDOT
Dave Morgan, RIDOT
 This work was sponsored by RIDOT Materials and Quality Assurance.

2. Motivation: Drawbacks of Current Inspection Techniques
Subject to the inspector
Inspector must see damage
Inspector must hear delaminations
Impacts traffic
Lane closures
Advanced levels of deterioration
More costly to repair
Visual Inspection
Visual inspection does not lend itself to subsurface evaluation, as the human eye cannot see below the surface where damage starts long before it is visible on an outer surface
Chain drag evaluation does somewhat lend itself to a subsurface evaluation, but may result in subjective findings, and inaccurately identified locations of damage.
Furthermore, chain drag evaluations always require lane closures, causing disruptions to regular traffic flow, and cannot be completed on overlaid structures.
Chain Drag

3. Goal of this Project Use NDT Techniques to: Infrared Thermography
Determine overall damage quantities
Locate specific areas of damage
Have higher confidence in these quantities/locations by combining the results of two methods
Infrared Thermography
Ground Penetrating Radar

4. IR and GPR Background Emitted IR Energy Concrete/steel Reflections
When deterioration exists in the deck, such as rebar corrosion, the concrete/steel signal reflection which appears as a hyperbola in a cross-sectional view of the deck, has a decreased amplitude in comparison with an area of the deck free from deterioration.
As rebar corrosion progresses, delaminations, or air/water pockets develop above the rebar. The air pocket acts as an insulator, and when the deck is heating up as the day begins, more energy is emitted from locations that contain delaminations below the surface, and appear as hotter temperatures.
Concrete/steel Reflections

5. Case Study Overall Damage Quantities: GPR: 7% IR: 0%
Spatial Agreement= 93%
As previously discussed, a delamination can be detected by a sudden change in spatial temperature of at least 2 degrees Celsius.
By viewing the color contour plot’s scale, one can easily notice that the variation throughout the entire deck is only 3 degrees Fahrenheit. This indicates that delaminations are not evident within this deck.
Similarly, the GPR rebar reflection amplitudes vary only 4.5dB throughout the entire lane. For comparison, a bridge deck with deterioration in the form of rebar corrosion will have amplitudes that vary between 15-20dB. This indicates that minimal or no damage exists in the deck.
To further quantify the results, after the GPR and IR data were processed further to develop appropriate thresholds, and each coordinated (X,Y) assigned a title (damaged/healthy), each coordinate were compared spatially. The IR data indicated that 100% of the deck was healthy and GPR indicated that 93% of the deck was healthy - due to varying concrete cover depths.
Therefore, the methods have a 93% spatial agreement, that the deck is healthy.
To validate these findings, three cores (4inches in diameter) were extracted from various locations on the deck.
GPR IR

6. Thank you