Corrosion protection of steel reinforcement in concrete structures by cathodic protection (CP) is a cost effective, reliable, and widely accepted method to stop and prevent the corrosion of the steel reinforcement. The efficiency of CP is usually monitored by the ''24 h, 100 mV depolarization criterion,'' a purely empirical criterion whose implementation is cost and labor intensive and that does not allow online control of CP. Within an extended research project on CP applied to concrete members of a highway bridge exposed to penetrating moisture, three sets of macrocells (MC), each composed of five MC sensors, were installed in conjunction with concrete resistance sensors and silver/silver chloride reference cells. Chloride profiles were determined from the cored or drilled powder originating from the installation of sensors and from drilling cores. Corrosion currents, steel potentials, and concrete resistance were monitored over a period of 1 year before, after installing the CP systems (which remained switched off for half a year for evaluating the effect of the conductive coating), and after startup of the CP systems. The CP systems applied consist of a moisture resistant conductive coating. As expected CP has a pronounced effect on local MC currents: Anodic MC currents were reduced or changed into cathodic currents, whereas cathodic currents were only weakly influenced. By adjusting the applied protection current all anodic MC currents may be changed into cathodic MC currents. Results indicate that the 100 mV depolarization criterion is a conservative criterion in atmospherically exposed concrete; it is not reliable in strongly wetted concrete. There was no consistent correlation between the CP induced changes in the local MC currents and 24 h depolarization values indicating that large potential shifts induced by CP do not necessarily imply overprotection. Results show that monitoring MC currents before, during, and after CP operation allows to demonstrate in a transparent way the effect of CP on the corrosion of the steel reinforcement. Online monitoring of MC currents is proposed as a viable and comprehensible method to monitor and control the efficiency of CP.
A galvanic zinc anode system, composed of a zinc mesh embedded into a proprietary solid matrix with ion exchange properties, was developed by CAS. The solid matrix of the embedded zinc anode system (EZA) is based on a tecto-alumosilicate-binder containing additives that prevent passivation of the zinc anode, assure high and durable galvanic activity of the zinc anode and high and durable adhesion towards the concrete overlay. The efficiency of the EZA, applied to concrete members of four types of civil structures – abutment of a road bridge in the Styrian Alps in Austria (2007), support-beams for the bearings of four viaducts in Den Hague in the Netherlands (2009) and a parking deck in Saas Fee in Switzerland (2011), was monitored with embedded reference cells and macro cell sensors. Data collected over a period of up to 10 years show that the EZA protects the steel reinforcement efficiently and reliably. An advanced EZA system – based on the novel shrinkage controlled EZA binder (SEZAC) covered with a novel water vapor permeable epoxy/PU membrane was installed July 2017 at the tunnel entrance of a federal road in the Styrian Alps. The EZA exposed to harsh weathering conditions proves to be efficient in protecting the steel reinforcement from corrosion.
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