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In order to properly repair the thousands of bridge decks in poor condition throughout our Nation, it is crucial that they undergo accurate and complete inspections, internally as well as externally. Current inspection techniques, like visual inspection, lack the ability to obtain detailed information inside of the deck, and can lead to an inaccurate assessment. Ground penetrating radar is a commercially available technology which can examine the internal composition of the deck at highway speeds. However, due to the lack of a threshold, necessary to distinguish healthy from corroded areas, the assessments must be completed by experienced practitioners. Previous work has demonstrated a method for establishing a threshold using hand operated, ground coupled GPR equipment. The research presented in this paper seeks to extend these thresholding concepts to high speed, air coupled GPR systems. Three in-service bridge decks, and four sawcut slabs of a bridge deck removed from service were assessed with a 2GHz air coupled antenna. Once the data from each deck were extracted at the rebar level and depth corrected, descriptive statistics, like the mean and skew were computed for each. These statistics were then multiplied together for each deck and plotted against actual deterioration quantities computed using half-cell potential measurements previously obtained. An 88% correlation coefficient was computed for these quantities, showing promise in these initial stages of the ...

ABSTRACT
Accurate measurement of pavement thickness is an essential aspect of the quality assurance of new pavement construction. Current methods involving the use of cores are time consuming and provide a very limited representation of the overall pavement structure. The overall objective of the work described in this paper was to rapidly determine the average pavement thickness on a newly constructed section to within 2.5 mm of the true value, without extensive reliance on cores. The effort was divided into two tasks-one for asphalt pavement and one for concrete pavement. The asphalt task has focused on two adaptations of ground penetrating radar (GPR), one involving the use of an air-launch horn antenna, and one using dual ground-coupled antennas in a common midpoint (CMP) measurement mode. The concrete task is focused on the GPR CMP method, and on adaptations of conventional impact-echo. The work included laboratory testing on small slabs and simulated pavement materials, testing at research pavement test facilities, and testing on actual roads in service in California. The pavement thickness data was correlated with thickness results obtained from over 200 cores taken at points in the test areas. The results show that, with proper implementation, the proposed methods can successfully achieve the desired objective. The paper describes the techniques, the testing d