Chloride Migration Variability in Reinforced Concrete Highway Structures in Pennsylvania

To assess the potential design life for reinforced concrete highway infrastructure in the Northeastern United States, the resistance to corrosion must be known. Reinforced concrete structures in both cold and marine environments are exposed to chloride, an ion with the potential to migrate through concrete and corrode steel. Chloride content can be assessed relative to the chloride migration coefficient determined at an age of 28-days using methods defined in NT Build 492. This approach is a departure from traditional rapid chloride permeability testing methods used for qualification of concrete mix designs by state departments of transportation. To investigate the impact of these methods, a comprehensive experimental study of PennDOT qualified mixes was conducted. Each mix was procured from ongoing construction efforts in the state and subject to both NT Build 492 and ASTM C1202 (Rapid Chloride Permeability Test). The results show that chloride migration coefficient varies considerably throughout the state, from 0.545 x 10-12 m2/sec to 17.24 x 10-12 m2/sec. The variation is in line with the results from Rapid Chloride Permeability Tests (RCPT) conducted on the same mixes. Results for NT Build 492 also correlated strongly with results for the RCPT, despite high coefficients of variability for both tests. Chloride migration was also found to be related to the coarse aggregate used in the mix design as well as the coarse aggregate’s absorption. Due to Pennsylvania’s diverse geologic make-up, 9 different types of coarse aggregate were used in the 20 mix designs tested. Mixes using Diabase and Dolomite as coarse aggregates were the most resistive to chloride migration, while mixes containing Gravel and Limestone experienced poor resistivity to chloride ingress. Coarse aggregate was sourced from 12 different counties in the mix designs tested. Results for NT Build 492 and the RCPT varied considerably in 5 of the counties