Abstract Manager

Transportation agencies increasingly require bridge structures to achieve design service lives of 75 to 100 years or more, particularly in aggressive environments where deicing salts, moisture, and brackish water accelerate deterioration. Chloride-induced corrosion of reinforcing steel in concrete and corrosion of exposed steel components remain the dominant mechanisms governing durability, maintenance needs, and life-cycle costs. The Harry Nice/Middleton Bridge over the Potomac River, connecting Maryland and Virginia, represents a complex durability challenge due to its wide range of exposure zones, including submerged, splash, buried, atmospheric, direct, and indirect deicing environments. Addressing these diverse conditions required a shift from prescriptive material specifications to a performance-based, service-life-driven design methodology

This paper presents the comprehensive corrosion protection and durability design framework developed for the Harry Nice/Middleton Bridge to satisfy element-specific service life requirements for both replaceable and non-replaceable components. The approach integrates laboratory testing, mechanistic modeling, and probabilistic analysis to manage uncertainty and provide a rational basis for material selection, detailing, and protective strategies. Key issues addressed include chloride ingress into concrete, variability in material properties, exposure-dependent corrosion mechanisms, and the interaction between concrete and steel deterioration processes.

Concrete durability was evaluated using probabilistic service life modeling in accordance with fib Bulletin 34, with corrosion initiation defined at a target reliability index corresponding to a 10% probability of initiation. Project-specific material properties were established through laboratory testing, including NT Build 492 chloride migration testing and AASHTO T277 electrical resistivity testing, to quantify concrete permeability and resistance to chloride penetration. The modeling framework incorporated critical parameters such as chloride migration coefficients, cover depth, surface chloride concentrations, reinforcement type, environmental exposure, and aging effects. This enabled the determination of maximum allowable chloride migration coefficients for different structural elements and optimized selection of concrete mixes, supplementary cementitious materials, and reinforcement systems.

Steel components were evaluated separately but in coordination with the concrete analysis. Buried and submerged steel elements were designed using corrosion allowance (sacrificial thickness) approaches based on in-situ corrosion rates, while exposed steel components were protected using coating systems designed in accordance with ISO exposure classifications and performance-based service life criteria.

The results demonstrate that combining project-specific testing with probabilistic service life modeling significantly reduces uncertainty and enables optimized, cost-effective durability solutions. The proposed holistic corrosion protection plan provides a defensible, risk-informed framework for achieving extended service life targets, minimizing life-cycle costs, and supporting sustainable design of critical transportation infrastructure.