Marine environments can be very aggressive and present significant challenges in maintaining key infrastructure from the effects of corrosion. In Florida, thousands of bridges are in coastal areas and are continually, or periodically exposed to saltwater conditions. A clear majority of these bridges were constructed using steel reinforced concrete and are supported by precast pilings situated in saltwater, so for this reason, cathodic protection is a necessary strategy for controlling the effects of saltwater induced corrosion.
Toward the early 1980s, the Florida Department of Transportation (FDOT) began the evaluation of different approaches to control saltwater induced corrosion. Some of these included the use of integral pile jackets, specialty materials for concrete repairs, surface applied coatings and other innovative approaches utilizing galvanic anode technology. One such system was jointly developed with industry partners and sponsored by the Federal Highway Administration (FHWA) using integral pile jackets lined with expanded zinc mesh anodes to apply cathodic protection. This innovative approach provides for the problem of concrete repair while at the same time stopping the on-going process of corrosion both combined in one application. Both laboratory and field trials validated the benefits to this approach and confirmed that the system can mitigate corrosion and extend the useful service life of pilings by more than 20 years.
This paper will present the findings and evaluation of two decommissioned pilings from the Veterans Memorial Bridge in Florida that had been protected using zinc mesh cathodic protection jackets for 21+ years.
Most metals are found in nature as ores or oxides. Only gold, silver and sometimes copper remain elementally stable when extracted from the ground. In the case of steel, iron ore is extracted from the earth, separated, refined, melted and alloyed to produce the end-product of steel. This process utilizes energy in the form of heat and mechanical processing to convert the iron ore into steel. That energy remains stored in the manufactured material until the energy is released by an electrochemical reaction between the metal and its environment. The natural tendency of a metal to react with the environment, or corrode, is an electrochemical process, which consists of four components: an anode, where oxidation occurs; a cathode where reduction occurs; a metallic path, where current flows; and an electrolyte, where ion transfer occurs. If any one of the four elements of the electrochemical cell are eliminated, corrosion cannot occur.