ABSTRACT

One of the methods of corrosion protection of metal reinforcement in concrete is cathodic protection. This protection can be achieved by different arrangements including sacrificial coatings. Several companies have made an attempt to create such a product, including NASA, and others. The goal of this study was to evaluate one existing formulation and optimize the corrosion protection by adjusting powders, resins, and installation techniques. A number of electrochemical techniques were utilized for measuring parameters of the galvanic coating. These laboratory and field techniques include electrochemical potential, electric resistance, corrosion current, and others.

INTRODUCTION

Corrosion is a problem in the US that costs billions. The latest study by the Federal Highway Administration estimated the direct costs of corrosion to be $276 billion-approximately 3.1% of the nation?s Gross Domestic Product (GDP). Based on the National Bridge Inventory Database, there are 586,000 bridges in the United States. Of this total, 435,000 bridges are made from steel and conventional reinforced concrete, 108,000 bridges are constructed using pre-stressed concrete, and the balance is made using other materials of construction. Approximately 15 percent of the bridges are structurally deficient, primarily due to corrosion of steel and steel reinforcement. The dollar impact of corrosion on highway bridges is considerable. The annual direct cost of corrosion for highway bridges is estimated to be $8.3 billion, consisting of $3.8 billion for the annual cost to replace structurally deficient bridges over the next 10 years, $2.0 billion for maintenance and cost of capital for concrete bridge decks, $2.0 billion for maintenance and cost of capital for concrete substructures (minus decks), and $0.5 billion for maintenance painting of steel bridges. Life-cycle analysis estimates indirect costs to the user due to traffic delays and lost productivity at more than 10 times the direct cost of corrosion.1 Cathodic protection is an electrochemical method of the corrosion control in which the oxidation reaction in a galvanic cell is concentrated at the anode to suppress corrosion of the cathode at the same cell. In cathodic protection the anode is often "sacrificed" to corrosion in order to protect the cathode. In practice, cathodic protection is primarily used for the protection of carbon steel. Commercial sacrificial anodes include magnesium, zinc and aluminum alloys.

Historically several criteria have been used to verify performance of cathodic protection from corrosion:

  • A uniform potential on the structure, which would eliminate galvanic cells between different regions.

  • A shift of the potential, from native or unprotected potential to a more negative, protected potential (-50mV to -300mV).

  • A shift of the structure potential to a potential at which current will flow into the structure instead of away from it. Later, a -850mV or -950mV vs. Cu/CuSO4 electrode was accepted and widely used for its simplicity and convenience for evaluation. An "instant off" of -850mV and a -100mV shift in potential are also in use as criteria.2

Concrete structures normally rely on the concrete cover to provide protection that prevents the corrosion of embedded steel. Over time, this protection can be lost due to moisture and/or chloride ingress.

This content is only available via PDF.
You can access this article if you purchase or spend a download.