Reinforced concrete is, in general, a very durable system. However, as designers pursue more efficient structural designs and subject these structures to more aggressive environments, these systems become increasingly susceptible to corrosion. Corrosion of steel reinforcement is one of the more prevalent mechanisms of deterioration in reinforced concrete systems. As the world’s infrastructure ages, the cost of repair and replacement of these systems increase at rapid rates. As new models, designs, materials and construction methods become available, the service life of these systems should be extended. This Special Issue initially focuses on current practices used throughout the world to mitigate corrosion of the steel reinforcement embedded in concrete. Alexander et al., Li and Ueda, and Geiker et al. provide an overview for durability based design in South Africa, Asia and Europe. The authors note that both prescriptive- and performance-based methods are currently in use with the objective of ensuring durability. All authors note the use of models, especially models to predict the ingress of chlorides into concrete, should be used to better predict the service life. However, Alexander et al. critique exposure classifications and conclude that both rational service life designs and relevant environmental exposure classifications are sorely needed. The authors also recommend that exposure classifications account for the various factors that influence reinforcement corrosion and the resulting structural damage. Li and Ueda review the state-of-the-art of durability design in Asia and highlight the strengths and weaknesses of the current practices. The authors ultimately recommend a ‘multi-barrier’ strategy to achieve long-term performance and corrosion resistance of reinforced concrete systems. Geiker at al. provide a European perspective on durability design and argue that designers must understand basic deterioration mechanisms and resulting damage to better design the infrastructure systems. The authors also note that service life models should include the time from corrosion initiation to the end of life (i.e., the propagation phase) to provide more resilient designs.
In addition to the design for durability perspectives from the different regions, understanding how to better predict and quantify factors that influence the service life are critical for improving resilience. Ogunsanya et al. present how the use of different de-icing chemicals can influence the critical chloride threshold, a critical parameter for assessing service life. Boschmann Käthler et al. present a review of how the critical chloride threshold values are assessed and make recommendations on how to quantify these critical chloride values. Interestingly, such a critical parameter for assessing the service life of reinforced concrete system has no standardized testing protocol (although advances are underway in several locales). Ahmed and Vaddey present interesting work on chloride testing of various cementitious systems and recommend that water-soluble chloride testing be used to quantify chlorides in concrete. Standardizing testing requirements are essential for ensuring corrosion-resistant structures and yet the pursuit is on-going. Shakouri and Dhandapani & Santhanam focus on build-up and transport rates of chlorides in concrete systems. Shakouri reported on the surface build-up rate of chlorides and assesshow these build-up rates influence service life. He concluded that a universal test is needed to assess surface chlorides; interestingly, this is another critical input parameter for assessing the service life and yet there is limited standardization. Shakouri also reported the need for long-term field data. Dhandapani and Santhanam compared various test methods currently used to quantify chloride transport rates under various exposure conditions and report good correlation between several testing methods.
Although much of the literature on chloride transport and service life of reinforced concrete systems focus on uncracked concrete, cracking in concrete is common. Yet limited work has been performed to assess how cracks influence corrosion and resulting service life of reinforced concrete systems. O’Reilly et al. assessed the corrosion performance of reinforced concrete specimens containing narrow cracks and reported that these narrow cracks can promote corrosion and potentially reduce the service life and resiliency of reinforced concrete structures. Because reinforced concrete systems can crack, efforts have focused on isolating the steel reinforcement surface from the aggressive salts that penetrate the concrete. Kamde et al. investigate the use of epoxy-coated reinforcement and recommend that more comprehensive and stringent specifications for this reinforcement may be needed to ensure corrosion resistance and resilience.
This Special Issue addresses several key issues and needs associated with resisting corrosion of steel reinforcement in concrete. However, much of the research associated with corrosion is laboratory based. And although laboratory data are essential for developing better models, better testing and better systems, it is essential that these laboratory data be validated with field data. Pacheco and Tepke provide a good overview of best practices for measuring, sensing and quantifying corrosion in reinforced concrete systems. These best practices should be used to generate longer-term data to ensure resilient and safe infrastructure systems.
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Notes on contributors
David Trejo
David Trejo is Professor and Hal D. Pritchett Endowed Chair in the School of Civil and Construction Engineering at Oregon State University, Corvallis, OR, USA. His research interests include sustainability and resilience of infrastructure systems, with focus on service-life analyses, innovative materials and systems for improved sustainability and resiliency, and quantifying and modeling deterioration mechanisms for improved performance and resiliency predictions.
Radhakrishna Pillai
Radhakrishna G. Pillai is a professor in the Department of Civil Engineering at IIT Madras, Chennai, Tamil Nadu, India. His research interests focus on steel corrosion and its impact on the durability and service life and resilience of concrete structures. His research focuses on developing corrosion test methods, developing database for assessing durability, cathodic protection, and extension of the residual service life of concrete structures.