Durability in Design of Light Rail Reinforced Concrete Structures

Recently, a number of light rail systems have been built or extended in North America. Typical design lives of metallic and concrete transit structures are required to exceed 75 y, with exposure to de-icing salts, freeze/thaw, and the potential for stray currents. Measures to mitigate the risks of reinforcement corrosion to rail structures have progressed over the last century, with some diversion between the preferred practices in Europe and North America. One significant difference with large cost impacts on projects is the means and methods to achieve continuity of the reinforcing steel within rail structures to control stray currents to negligible levels. Herein we review the available standards and literature as it relates to the risks of stray current corrosion of reinforcing steel, specifically with respect to the requirement for welding reinforcing. Field measurements of steel resistivity taken during the construction of rail structures are presented to clarify the as-built condition. Taking into account the effect of stray currents on the chloride threshold for corrosion initiation, methods are recommended to achieve durability requirements for the least lifecycle cost to asset owners.