Quantitative Patina Rating Index for Weathering Steel Bridge Girders

Weathering steel is a low maintenance and cost-effective corrosion-resistant material that is widely used in bridge construction. The corrosion rate of weathering steel is known to be lower than carbon steel in a low- and medium-corrosive environment. This is because of the inherent corrosion resistance of the patina layer, which adheres to the substrate and protects the weathering steel from further corrosion. There are multiple guidelines to evaluate the protective performance of the rust layer that mainly emphasize visual inspection of the color and texture of the patina. However, these standards are, in general, qualitative and subject to observer bias. The tape adhesion test is one of the examinations proposed in the past that is less subjective, and it can be used to assess the functionality of patina to ensure the layer protects the underlying steel. The interpretation of the test results still relies on a partially qualitative judgment rather than a limited quantitative analysis. The objective of this research is to develop a reliable framework that can be used alongside visual inspections to increase accuracy in measurements. A Quantitative Patina Rating Index has been introduced in this paper, which was built on image analysis of 444 tape adhesion test samples, obtained from various macro and micro environmental conditions. The rating accounts for the size and the areal density of rust particles recorded on the tape samples and classifies patina in different categories. This classification will aid bridge owners and stakeholders in making more informed maintenance and inspection decisions.