Impact of environmental factors on condition assessment of concrete bridge decks using nondestructive testing

Abstract

Reflection of Ground Penetrating Radar (GPR) amplitudes from rebars is an important parameter for assessing current condition of concrete bridges. GPR reflection amplitudes may be influenced by several factors, including chloride content, rebar corrosion, and environmental conditions at the time of data collection. The objectives of this study are to observe the change of GPR signals over time and to evaluate the effect of environmental conditions on GPR reflection amplitudes. A series of six reinforced concrete bridge deck slabs were fabricated with varying chloride contents, from 0.02 percent to 0.1 percent. Corroded rebars were used to examine any corrosion impact on GPR signal attenuation. In the first testing phase GPR data was recorded daily for 90 consecutive days. After 90 days, the specimens were sprayed with water, and GPR data was collected to study the effect of surface water on GPR amplitudes. Specimens were then placed in an environmental chamber in a second testing phase where relative humidity (RH) was set at three levels. Temperature for each RH level was varied from 5◦C to 40◦C. Both the increased chloride content and rebar corrosion resulted in reduction of GPR reflection amplitudes. GPR reflection amplitude of corroded rebars was found to be smaller than that of non-corroded rebars. GPR reflection amplitudes for concrete specimen with no chloride content decreased by approximately 0.05 dB for every 1◦C increment. The higher the chloride content the higher the GPR reflection amplitude. The RH was observed to have an insignificant effect on GPR reflection amplitudes. This study will greatly benefit the West Virginia Department of Transportation as the agency continues to safely preserve over 7,200 bridges.