Project Description:

Chloride-induced corrosion of reinforcing steel is one of the most significant durability challenges facing concrete infrastructure, especially for bridges, pavements, and marine or deicing-salt exposed structures. A critical parameter controlling corrosion initiation is the critical chloride threshold (CT), yet existing test methods produce inconsistent values and do not fully reflect the behavior of modern concrete mixtures containing supplementary cementitious materials (SCMs) or waste-derived additives. As transportation agencies adopt newer binder systems such as Type IL cement and increase the use of SCMs, the need for reliable, practical, and reproducible CT measurement techniques has become increasingly important for service-life design.

This project addresses these needs by evaluating how Class C fly ash, Class F fly ash, and metakaolin, each applied at two replacement levels with Type IL cement, affect the CT of reinforced concrete. The study employs the newly developed OCcrit test method (Figure 1), which measures CT directly on mortar specimens under controlled electrochemical conditions. OCcrit offers improved reproducibility and more realistic assessment of steel–concrete interactions compared to traditional embedded-bar or potentiometric techniques, making it a promising method for future durability evaluations.

In parallel, the project will investigate a second approach to CT measurement using cyclic polarization. While this method has previously been applied only to steel samples immersed in simulated concrete pore solutions, results have not aligned with OCcrit values which is believed to be due to the absence of true concrete environments. Leveraging a high capacity potentiostat, this research will apply cyclic polarization directly to mortar samples for the first time, enabling a meaningful comparison with OCcrit and helping determine whether the method can be adapted into a practical tool for corrosion threshold assessment.

Finally, the project will examine the role of waste-derived materials by assessing the influence of acid- and base-pretreated ground tire rubber (GTR) on CT. Previous studies showed that untreated GTR can affect corrosion initiation, but the mechanisms remain unclear. By evaluating chemically surface modified GTR using the OCcrit method, the project will clarify how surface treatments alter particle–matrix interactions, pore solution characteristics, and overall corrosion behavior. The combined findings will provide transportation agencies with more accurate data and improved testing methods for designing durable, long-lasting concrete infrastructure exposed to chloride environments.

The proposed research directly aligns with CHDT’s core mission to enhance the durability and service life of transportation infrastructure through innovative materials and techniques. CHDT emphasizes the development of sustainable, performance-driven construction materials, particularly the reuse of recycled and waste materials such as rubber and industrial by-products, to improve structural longevity and reduce maintenance costs. By evaluating how SCMs and treated GTR influence corrosion resistance and by advancing CT testing methods, this project extends CHDT’s ongoing portfolio of work on freeze-thaw durability, corrosion mitigation, and the beneficial use of waste materials in concrete pavements.

US DOT Priorities:

This project supports U.S. DOT priorities by improving the durability and reliability of concrete in transportation infrastructure, thereby increasing safety, reducing lifecycle costs, and enabling more efficient system performance. By identifying how SCMs and treated waste materials influence corrosion initiation and by advancing more accurate CT testing methods, the research helps prevent premature deterioration of bridges and pavements which will reduce failures, unplanned closures, and maintenance interruptions.

Outputs:

This project will generate a comprehensive dataset on how Class C fly ash, Class F fly ash, metakaolin, and chemically pretreated ground tire rubber influence the critical chloride threshold of Type IL concrete, using both the OCcrit method and cyclic polarization applied directly to concrete. It will also produce refined testing protocols, guidance on data interpretation, and service-life modeling inputs derived from the measured thresholds. Additional outputs include mixture characterization results, technical documentation, sharable datasets, peer-reviewed publications, conference presentations, and a final technical report to support broader adoption of improved durability assessment methods by transportation agencies.

Outcomes/Impacts:

The outputs of this project will enable transportation agencies to more accurately assess and predict corrosion initiation in reinforced concrete, leading to improved service-life modeling, more durable mixture designs, and better-informed performance-based specifications. By providing validated chloride threshold data for SCM- and GTR-modified concretes, the research will support broader adoption of sustainable materials without compromising durability, helping agencies reduce lifecycle costs and extend the time between major repairs. The refined OCcrit and cyclic polarization methods will offer transportation practitioners more reliable tools for evaluating corrosion risk, encouraging a shift toward more proactive maintenance strategies and potentially informing updates to testing standards or state-level material guidelines. Collectively, these outcomes will enhance the safety, reliability, and durability of transportation infrastructure by decreasing premature deterioration, reducing unplanned closures, and lowering long-term maintenance demands