SIMULATED GPR INVESTIGATION OF DETERIORATION IN REINFORCED CONCRETE BRIDGE DECKS

The objective of this paper is to use advanced modeling capabilities to represent different cracking schemes around reinforcement steel and chloride-graded concrete to determine potential relationships between measured GPR signals and attenuation, and potential deterioration states of bridge decks. The American Society of Civil Engineers determined that, in 2009, more than 26% of bridges in the United States were structurally deficient or functionally obsolete, and that there is a significant cost associated with maintaining the current level of deficient bridges (roughly $13 billion a year, according to AASHTO). Non-destructive testing, such as ground penetrating radar (GPR) surveys, can help to determine the condition of bridges. These investigations have a significant advantage over traditional visual inspection in that the condition of the subsurface can be inferred before damage has progressed to the point of being visible at the surface. This information can be extremely valuable in the scheduling and allocation of resources for repair and rehabilitation. The examination of the data from GPR surveys reveals significant attenuation of the signal scattered from the rebar in areas of concrete contamination and rebar corrosion. However, it is unclear if this attenuation is due to geometric changes in the bridge deck, such as cracking and debonding around the corroding rebar, changes to the electromagnetic properties of the surrounding concrete, e.g. due to chloride infiltration, or a combination of the two. Using finite difference time domain modeling of electromagnetic wave scattering the contribution of these factors is considered to obtain signal attenuation matching results observed in the field. It was found that the attenuation of the signal due to severe cracking does not govern over the variation of moistures and chlorides (or permittivity and conductivity) throughout the bridge deck.