Civil infrastructure immersed in natural waters is subjected to physical, chemical and biological interactions with the environment that can result in material degradation. Corrosion is of particular concern due to its adverse effects on the mechanical integrity of steel structural elements, but other natural interactions of steel in the marine environment such as marine fouling can intersect, creating complex systems exacerbating material degradation. Cathodic protection (CP) can be applied, but complications arise in the marine environment. Shielding of current due separation of the steel surface from the bulk solution can develop with the presence of uniform fouling encrustations. The objective of this research here was to provide field data on the total currents provided by a galvanic CP system to steel immersed in bridge environments that support macro- and micro- fouling. Field testing incorporated steel arrays submerged in two Florida natural water bodies that could sustain typical fouling. Bulk zinc anodes provided beneficial cathodic polarization of the steel array (<-1000 mVSCE and >10mA) that significantly decreased the overall corrosion rate, but localized corrosion still developed below fouling encrustations. Smaller local CP currents were measured where uniform and compact fouling and calcareous deposits formed. Testing indicating that the barrier provided by the fouling layers and surface deposits do not provide overall corrosion protection but fouling layers can reduce the available surface area to support cathodic reactions.
