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Technical Tip steel tie. The steel tie portion of the anode is subjected to corrosion, as well; therefore, using a corrosion-resistant material such as galvanized steel for the tie-downs is important. If the ties corrode prematurely, the anode is no longer attached to the reinforcing bar and protection will not occur. Eventually the anodes require replacement. However, this replacement lasts approximately two to three times longer than conventional con- crete before it would need to be repaired, and the replacement is, for the most part, easier than a standard repair (as long as the replacement takes place before corrosion is able to reach the rein- forcing bar). There are various testing procedures used to determine when the anodes need to be replaced. Once this testing indicates that it is time to replace, the area around the anode is saw cut and chipped away to reveal the reinforcing bar and a new anode is attached. Repair material Fig. 4: Sentinel install comprised of similar material to the original chloride movement is slowed to the point that the structure is recommended to maintain the same protective coverage range of the anodes is spacing criteria. reduced significantly. For this reason, the spacing The use of shotcrete as a base material, as of the anodes is reduced to ensure protection of well as a repair process, is continually growing the steel. Determination of the resistivity is rec- in popularity. The use of cathodic anodes as a ommended in all projects and is essential in method of corrosion protection is also popular shotcrete projects. Determining the mixture with historical success. The combination of the resistivity, as stated earlier, is fairly simple and two materials is an obvious good fit. Initial time, inexpensive. The Florida DOT has done extensive labor, and material costs are overcome by the testing and published the data and results. This savings that are experienced by extended repair paper is available on the Florida DOT website. time cycle. The type of anodes themselves plays a large Reference role in the protection. Typically, the contact area “Cathodic Protection Systems—Use of Sacrificial or between the anode and reinforcing steel should Galvanic Anodes on In-Service Bridges,” NYSDOT Office be stable and insulated to contact only at the ends of Operations, Transportation Maintenance Division, Bridge to prevent “dumping of current” onto the rein- Maintenance, 2008, 24 pp. forcing bar. This current dumping can lead to overloading the cathodic protection system and cause premature failure of the anodes. Also, the Jesse Osborne is currently the amount of sacrificial material that is used (zinc, Mining and Tunneling Segment in most cases) will play a significant role in the Manager for The Euclid Chem- amount of protection and the life span of the ical Company, based in Cleve- anode. Using more zinc in the anodes is essential land, OH. He has been with in high-chloride environments. Increasing the Euclid Chemical for over 10 service of the anodes prolongs the time interval years and has over 30 years of for anode replacement, which obviously saves experience in the concrete and more money. The anodes need to be attached to cement construction industry with positions the reinforcing bar in a manner that will secure ranging from research and development to them as snugly as possible. They are usually product and segment marketing. He is a member attached to the reinforcement with some type of of SME and NPCA. 68 Shotcrete • Winter 2015


2015WinterShotcreteEMag
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