Replacing Thermal Sprayed Zinc Anodes on Cathodically Protected Steel Reinforced Concrete Bridges

摘要

This research aimed to address questions underlying the replacement of arc-sprayed zinc anodes on cathodically protected steel reinforced concrete bridges and to develop a protocol to prepare the concrete surface for the new anode, through a combination of literature review, practitioner surveys, laboratory studies, and field investigation (Pier 9 of the Yaquina Bay Bridge, Oregon). Concrete with an equivalent electrochemical age of 5 to 45 years was found to have a reaction layer of approx. 1 mm. To achieve strong initial bond strength of new zinc to the profiled concrete surface, the current ODOT sandblasting operating configuration (No. 8 nozzle with high sand volume) is too aggressive and should be changed to No. 6 nozzle with low sand volume to achieve target RMS macro-roughness of 1.2-2.1 centi-inches and micro-roughness of 3.5-5 Em. It is recommended to adjust the anode removal and surface profiling based on the electrochemical age of the existing concrete. Wherever possible, large aggregates (e.g., diameters . in. and bigger) should be avoided for exposure by surface profiling. For non-electrochemically aged concrete, the surface should be profiled to achieve a RMS macro-roughness of 1.1-1.8 centi-inches and 5-36% exposed aggregates. For existing concrete with relatively high electrochemical age (14 yrs), the surface should be profiled to achieve a RMS macro-roughness of 1.1-1.5 centi-inches and 44-55% exposed aggregates. The following recommendations were made for old anode removal and surface preparation before new anode application: use a reasonably low air pressure and a reasonably hard and dense abrasive material for sandblasting; have a reasonably thin coating per pass during arc-spray operations; and have a slightly thinner overall Zn coating layer (15-17 mils vs. the currently used 17 mils).