Advanced nondestructive inspection techniques like stress wave timing and resistance microdrilling have been used to successfully inspection timber bridges, but it is most effective on girder style bridges. There is a noted need to develop additional inspection techniques for longitudinal deck/slab timber bridges, which comprise about 20% of the national bridge inventory. One technique that holds potential is ground penetrating radar, a recognized nondestructive testing technique that has been used effectively for many different environmental and transportation applications. It has been utilized successfully to identify buried objects, internal defects and material changes. The objective of this research was to assess the potential for using GPR to identify and assess simulated deterioration in longitudinal timber deck timber bridges. GPR scans were completed in the longitudinal and transverse directions of a screw laminated timber bridge deck before and after a bituminous layer was added to assess embedded defects that simulated voids, decay, insect damage and horizontal shear splitting. Assessment of the GPR wave energy signal was completed using visualization software that was provided with the commercial GPR unit used for the testing. The radar signal was analyzed in both the longitudinal direction (antenna front to back) and the transverse direction (antenna side to side). Interpretation of the radar signals allowed for the identification of various internal defects present in the deck. Based on the results, GPR has the potential to identify internal defects in timber bridge decks before and after a bituminous layer was added. Large, rectangular void defects (at least 6‐ by 12‐ by 5 in. (15.2‐ by 30.4‐ by 12.7 cm)) that were hollow, filled with foam, or filled with sawdust/adhesive were most easily identified under all scanning conditions. The addition of a bituminous layer, common to slab bridge construction, damped the signal response and made it more difficult to identify defects. Several smaller defects that were found in the deck without a bituminous layer were not identified in scanning completed after the bituminous layer was added.

Ground-penetrating imaging radar (GPIR) is proposed for large-area inspection of concrete and concrete/asphalt composite bridge decks and roadways. This technique combines ground-penetrating radar (GPR) with unique image reconstruction algorithms developed for identification and characterization of subsurface flaws and structural features. New data acquisition hardware and image reconstruction techniques, under development at LLNL, offer the possibility for reliable and efficient, high-resolution subsurface imaging through the use of improved ultra-wideband transmitters, antennas, and arrays, and enhanced image- and signal-processing software. A field test of a limited-capability prototype system is planned for FY-93, as is completion of a conceptual design for a practical inspection system. A follow-on program for FY-94 would focus on development and demonstration of an advanced bridge inspection system prototype based on the conceptual design completed during FY-93.

"The rapid growth of infrastructure in the UAE has caused a proportional growth in the transportation system. Bridges are among the major elements in the transportation system that requires continuous monitoring and maintenance over time. Replacement of bridges is expensive; hence it is desirable to assess damage using a cost effective maintenance strategy. Therefore, nondestructive testing techniques provide an efficient and feasible method for detecting defects in bridges in a quick manner. Several surveys have shown that ground penetrating radar (GPR) has the potential to be adopted as a non-destructive inspection technique. This work presents an experimental investigation of mix variation, and environmental conditions effects on the detectability of defects using GPR."--Abstract.

Inspecting high-value structures, like bridges and buildings using Ground Penetrating Radar (GPR) is an application of the technology that is growing in importance. In a typical inspection application, inspectors use GPR to locate structural components, like reinforcing bars embedded in concrete, to avoid weakening the structure while collecting core samples for detailed inspection. Advanced GPR, integrated with imaging technologies for use as an NDE tool, can provide the capability to locate and characterize construction flaws and wear- or age-induced damage in these structures without the need for destructive techniques like coring. In the following sections, we discuss an important inspection application, namely, concrete bridge deck inspection. We describe an advanced bridge deck inspection system concept and provide an overview of a program aimed at developing such a system. Examples of modeling, image reconstruction, and experimental results are presented.

"The present study is comprised of two separate GPR case studies on a bridge deck and a concrete pavement respectively. These typical concrete structures were investigated using GPR with several objectives: 1) to find the reason of discrepancies between GPR results and the results of the other tests through bridge deck inspection, 2) to investigate the bridge deck under various weather conditions, 3) to determine the relative spatial locations of the imbedded dowel bars in the new concrete pavement, and finally 4) to evaluate the present capabilities of GPR technology including survey scheme and analysis through these two case studies."--Abstract, p. iii.

The ASCE report card 2013 rated bridges at a grade of C+, implying their condition is moderate and require immediate attention. Moreover, the Federal Highway Administration reported that it is required to invest more than $20.5 billion each year to eliminate the bridge deficient backlog by 2028. In Canada 2012, more than 50% of bridges fall under fair, poor, and very poor categories, where more than $90 billion are required to replace these bridges. Therefore, government agencies should have an accurate way to inspect and assess the corrosiveness of the bridges under their management. Numerical Amplitude method is one of the most common used methods to interpret Ground Penetrating Radar (GPR) outputs, yet it does not have a fixed and informative numerical scale that is capable of accurately interpreting the condition of bridge decks. To overcome such problem, the present research aims at developing a numerical GPR-based scale with three thresholds and build deterioration models to assess the corrosiveness of bridge decks. Data, for more than 60 different bridge decks, were collected from previous research works and from surveys of bridge decks using a ground-coupled antenna with the frequency of 1.5 GHz. The amplitude values of top reinforcing rebars of each bridge deck were classified into four categories using k-means clustering technique. Statistical analysis was performed on the collected data to check the best-fit probability distribution and to choose the most appropriate parameters that affect thresholds of different categories of corrosion and deterioration. Monte-Carlo simulation technique was used to validate the value of these thresholds. Moreover, a sensitivity analysis was performed to realize the effect of changing the thresholds on the areas of corrosion. The final result of this research is a four-category GPR scale with numerical thresholds that can assess the corrosiveness of bridge decks. The developed scale has been validated using a case study on a newly constructed bridge deck and also by comparing maps created using the developed scale and other methods. The comparison shows sound and promising results that advance the state of the art of GPR output interpretation and analysis. In addition, deterioration models and curves have been developed using Weibull Distribution based on GPR outputs and corrosion areas. The developed new GPR scale and deterioration models will help the decision makers to assess accurately and objectively the corrosiveness of bridge decks. Hence, they will be able to take the right intervention decision for managing these decks.

"Integrated non-destructive techniques were utilized to assess the condition of a reinforced concrete bridge deck. There were two main objectives accomplished. The first objective was to assess the integrity of the reinforced concrete bridge deck using four non-destructive techniques, namely visual inspection, ground penetrating radar, portable seismic property analyzer-ultrasonic surface wave, and hammer sounding and chain drag. Visual inspection data were used to identify signs of deterioration on surface of the bridge deck such as cracking, concrete leaching, and reinforcement corrosion. Ground penetrating radar data were used to determine the relative condition of the bridge deck. However, due to the significant differences in depth of the embedded reinforcements, ground penetrating radar data were not useful in terms of assessing the overall condition of the bridge deck. Portable seismic property analyzer-ultrasonic surface wave data were used to determine the concrete quality of the bridge deck by estimating average Young's modulus (elastic modulus). Hammer sounding and chain drag data were used to identify non-delaminated and severe delaminated areas in the bridge deck. The second objective was to demonstrate the effect of temperature and moisture content changes on ground penetrating radar signal amplitude. Ground penetrating radar signal amplitude variations associated with different weather condition of temperature and moisture changes were evaluated. Ground penetrating radar signal amplitude was increasingly attenuated during low temperature and high moisture content. In contrast, ground penetrating radar signal amplitude was decreasingly attenuated during high temperature low moisture content"--Abstract, page iii.

There is an urgent need for methods that can be used to rapidly and nondestructively determine the condition of an old concrete deck beneath an asphaltic concrete wearing course. In recognition of this need, the technique of ground-penetrating radar was investigated. In practice, microwave-frequency impulses of about 1.1 nanosecond pulse width are transmitted into an overlaid bridge deck by a radar transducer that also serves as a receiver. When these electromagnetic pulses are directed through a delaminated concrete area, there is some pulse reflection from the deteriorated concrete, (the more severe the delamination, the more pronounced the reflection), in addition to the normal reflections at the air-asphaltic concrete and asphaltic concrete portland cement concrete interfaces and the reinforcing steel. The reflected pulses are then picked up by the transducer and transformed into the audio frequency range by a time-domain sampling technique and displayed on a facsimile graphic recorder as a pulse reflection profile. Although intended for use on overlaid bridge decks, the technique was experimentally used on three non-overlaid concrete decks and two old concrete deck slabs, in addition to three overlaid decks. To obtain 'ground truths' for comparison, conventional soundings were performed on the non-overlaid decks and slabs and two of the overlaid decks after their overlayments were removed. The results showed that ground-penetrating radar can be used successfully to detect concrete delaminations in both nonoverlaid and overlaid bridge decks, since the delaminations are manifested in the recorded radar pulse reflection profiles as recognizable irregularities in the reflection bands corresponding to the top mat of the reinforcement. These irregularities, or signatures of concrete delaminations, were often in the form of depressions, but in some instances appeared as blurs or breaks in the profiles. It was also found that the radar sometimes missed small delaminated areas of about 1 ft. (0.3 m) width and less. However, this relatively small deficiency does not impair the overall effectiveness of the technique as a nondestructive inspection tool for both types of decks. The experimental procedure can be used as is to inspect decks, if lane closure is not a major concern. However, with little further experimentation, this requirement may be completely eliminated.