Condition Assessment of Concrete Bridge Decks using Ground Penetrating Radar

Highway bridge structures play a critical role in transportation system. While one-third of Canada’s 75,000 highway bridges have structural or functional deficiencies and a short remaining service life; in the United States (US), as of December 2013, more than 100 million m2 of the total 360 million m2 of concrete bridge decks is either structurally deficient or functionally obsolete. To eliminate that deficient backlog in US by 2028, it is estimated that an annual investment of $20.5 billion would be needed and the largest portion of this expenditure would be for bridge decks. Condition assessment of concrete bridge decks provides required inputs for programming deck maintenance activities. In both Canada and the United States, the main approach to evaluate condition of bridge decks, as for other bridge elements, is based on visual inspection. Although this approach may be effective in finding external flaws such as cracks, scaling and spalls; it cannot detect subsurface defects such as voids, internal cracks, delaminations, or rebar corrosion. To overcome such limitation of visual inspection, this research aims at developing a condition assessment system for concrete bridge decks based on nondestructive evaluation (NDE) technology. In order to achieve that goal, three research objectives were identified: (1) study and select the most appropriate NDE technology; (2) study methods for interpreting data of selected NDE technique; and (3) develop bridge deck corrosiveness index (BDCI) from NDE output. Ground penetrating radar (GPR) was found to be one of the most appropriate technologies for inspecting concrete bridge decks subjected to corrosion-induced deterioration. As for GPR data interpretation, two analysis methods are proposed in this research. The first one is an integrated technique between the amplitude method and visual interpretation with threshold calibration based on K-means clustering. The second approach is a technique for analyzing time-series GPR data. Based on correlation coefficient between A-scans, this technique assesses concrete deterioration by studying the change of GPR signals over time. Expert opinions, through a structured questionnaire survey, were used to develop and interpret bridge deck corrosiveness index (BDCI) based on GPR output. After being validated by several case studies, an automated software has been developed to facilitate the implementation of the entire methodology. The developed system and models will help transportation agencies to identify critical deficiencies and focus limited funding on most deserving bridge decks