CORROSION MITIGATION IN REINFORCED CONCRETE STRUCTURES USING ENGINEERED CEMENTITIOUS COMPOSITES
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Concrete is the most widely used construction material in the world. However, approximately 10% of the bridges in the United States, majority of which are made of reinforced concrete, are structurally deficient or functionally obsolete mainly due to corrosion. Every year, significant resource consumption and environmental degradation are associated with the maintenance and repair of corrosion-damaged reinforced concrete infrastructure. The fundamental reason behind the corrosion-related deterioration is the brittleness of concrete, which makes the unreinforced cover of all reinforced concrete structures prone to cracking under small tensile stress. Engineered Cementitious Composites (ECC) is a class of ductile fiber-reinforced cementitious composites with strain capacity under uniaxial tension greater than 1%. Compared to conventional concrete, ECC has been shown to mitigate the corrosion-related damage, primarily in the propagation phase of corrosion, due to small crack widths typically limited under 100 µm. As a result, ECC has been extensively investigated and applied in a few structures as an alternative to conventional concrete to improve the infrastructure durability and sustainability. Yet, little is known about the performance of ECC during the initiation phase of corrosion.The main goal of this dissertation is to investigate the corrosion protection offered by ECC during both the initiation and the propagation phases of corrosion, in comparison to conventional concrete. The investigation of corrosion initiation in reinforced-ECC specimens in this dissertation led to the development of two novel experimental methods for determining the critical chloride concentration (Ccrit) that is vital for determining the initiation of active corrosion and service life of reinforced concrete structures. One of the two methods utilizes existing electrochemical techniques to monitor corrosion but takes into account the observed corrosion pit depths and provides a more accurate determination of Ccrit compared to the existing methods. The other novel method is a rapid test that enables the determination of Ccrit within a few days instead of several years taken by the existing methods. The behavior of intact and damaged reinforced-ECC structural elements during the propagation phase of corrosion is addressed in this dissertation. The primary objective of this research was to determine whether using ECC only in the cover of reinforced concrete structural members is as effective in reducing corrosion damage as making the entire member with ECC. Furthermore, the quality of the interfacial bond between ECC and concrete was investigated, which confirmed the feasibility of using precast ECC covers as permanent formworks for reinforced concrete members. The results presented in this dissertation will form the basis for future utilization of ECC and similar advanced cementitious materials in infrastructure to achieve 100-year or longer service life.