Predicting concrete resistivity from Ohms law

The resistance of concrete to the penetration of chloride ions from deicing salts or other brine solutions is one of the most important performance properties used in concrete mixture design specifications. This property provides valuable insight into the time to the corrosion initiation of reinforcing steel. The AASHTO T277 or ASTM CI 202 tests have been used in the approval of mixture designs for most high performance concrete (HPC) specifications as an indicator of durability. This test is time consuming and not conducive to the volume or time constraints of quality control or quality assurance (QC/QA) testing of in-situ concrete or field cured concrete. In recent years, various iterations of the Wenner probe have been developed to characterize the electrical resistance of concrete, a property that plays an important role in the initiation and propagation of corrosion. Fully developed life cycle analysis models use both a) corrosion initiation time; and b) corrosion propagation components to address their goals. This thesis demonstrates that the physics of these two tests are closely related and using 26 different HPC mixture designs, the electrical resistivity can reliably predict the resistance of concrete to the penetration of chloride ions with substantially less effort and expense. In this large number of different mixture designs for bridge decks and exposed structures, the electrical resistance consistently correlated with the T277 and CI202 test results. In addition, the concrete's electrical resistance is a physical property of the concrete, not just an indicator of potential behavior. As such, it can be directly used in the development of corrosion models. This thesis discusses the research conducted to verify the correlation between the ASTM CI202 testing results and the Wenner resistivity results using Ohms law. Through this research, it was determined that there was a consistent relationship through Ohms law.