Title: A Novel "Coupled" Approach to Evaluate and Extend the Service Life of an Existing Structure

Author(s): Jacques Marchand

Publication: Web Session

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Date: 4/1/2021

Abstract:
Many key transportation assets such as tunnels and bridges were designed without considering that construction materials age and degrade over time when exposed to chemically aggressive conditions such as de-icing salts and seawater. Owners around the world are currently facing the challenging situation of having to extend the useful life of many of these structures. Although rehabilitation engineers have access to a wide range of proven solutions, there are few reliable tools to prioritize interventions and minimize the cost of repair. A new methodology was used to assess the current condition of existing reinforced concrete tunnels in exposed to chlorides from seawater or de-icer salts. The proposed technique goes well beyond the common chloride modeling by including calculations of the corrosion-induced section loss of reinforcing steel and its impact on the long-term integrity of the structure. Corrosion rates are determined by modelling the resulting electrochemical system between anodic steel reinforcement, embedded in chloride-contaminated concrete, and cathodic steel reinforcement, located in uncontaminated or less contaminated concrete. Analyses are performed with the STADIUM® and COMSOL™ Multiphysics software applications following a bottom-up approach. This approach employs the actual as-built section geometry and steel reinforcement layout, as well as the in-situ concrete and steel material properties gathered from field and laboratory testing. The resulting steel section loss curves generated at critical locations of the structure are then considered in calculations performed at different ages to evaluate changes in structural behavior at high-stress locations of the tunnel structural elements. Results from this novel structural engineering and material science “coupled” approach allow to reliably estimate the residual service life of the tunnel and develop recommendations to safely and cost-effectively extend the service life of the structure.