NCHRP, AASHTO, FHWA
This project will develop a new method for measuring chlorides in bridge deck concrete using ground-penetrating radar (GPR). Work on Stage 1 will focus on identifying the bridges to be tested, developing procedures for testing, and testing the selected decks. An analytical model that defines the relationship between chlorides in concrete and GPR measurement of conductivity by way of signal attenuation will be developed. A plan will be designed for proving the validity of the test model, which will consist of laboratory experimentation, in-situ GPR field testing and validation tests. Laboratory tests will be performed to establish the effect of chlorides and water on GPR signal propagation. Experiments will be performed with varying chloride quantity and moisture to observe their effect on radar signal attenuation and relative dielectric constant. Discussions with bridge owners will be conducted to select concrete and asphalt-covered bridge decks for testing. GPR data collection will be conducted at both low and high speed and with various types of GPR antennas. Concrete core samples will be collected and chloride ion analysis performed for comparison with GPR measurements. Work in Stage 2 will develop a practical method based upon data collected in Stage 1. Software and hardware will be developed that will involve incorporation of signal processing and improvements to algorithms to help accurately estimate chloride quantity in bridge decks. GPR bridge deck data will be analyzed and the relationship between GPR conductivity (attenuation) and chloride for each deck will be established. The relationship will be used to develop a topographical chloride mapping which will be back tested against ground truth to determine the accuracy rates. The minimum number of core samples required will be determined. A detailed final report will be prepared which will include all relevant laboratory and field data, as well as project findings along with plans for implementation.