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2017SummerShotcreteEMag

corrosion-inhibiting admixtures have been certified to meet ANSI/NSF 61 requirements for safe use in structures containing potable water. Recent testing indicates that certain migrating corrosion inhibitor technologies are also compatible with CP systems, in some cases reducing the current requirement.4 CORROSION-INHIBITING PERFORMANCE The use of migrating corrosion inhibitor admixtures can double or triple the time to corrosion initiation and, once corrosion starts, reduce corrosion rates by five to 15 times compared to a control.1 Compared to other admixtures, such as CNI or amine esters, they do exceptionally well under modified ASTM G109 testing (refer to Fig. 3). This testing introduces cracks into the concrete test specimens, making it easier for corrosive elements to reach the surface of the reinforcing bar. In one example of this, corrosion rates for samples treated with a migrating corrosion inhibitor admixture stayed significantly lower than those of CNI and amine-ester treated concrete during 20 cycles of saltwater ponding.5 USES OF MIGRATING CORROSION INHIBITOR IN SHOTCRETE Migrating corrosion inhibitor technology has more than 30 years of historical use in reinforced concrete, and more than 15 years of use with shotcrete applications. As far back as 2001, a repair project using migrating corrosion inhibitors won an ICRI Award of Excellence for the Transportation category. The project involved repairing the Crib Point Jetty in Western Port Bay, Victoria, Australia. The jetty had experienced substantial spalling, cracking, and degradation caused by corrosion in the harsh concrete environment. The degraded concrete and steel reinforcement was removed from any of the deteriorating concrete piers and beams, and new reinforcement was added as needed. The repair was completed by applying shotcrete repair mortar that contained migrating corrosion inhibitors to reduce further corrosion in the structure.6 Tunnels and Bridges In the state of Pennsylvania, District 11 has used a migrating corrosion inhibitor in its wet- and dry-mix shotcrete for over 8 years. In patched areas, PENN DOT has included an anode system for extra protection. One of these projects was the repair of the Liberty Tunnel in Pittsburgh (refer to Fig. 4 and 5). Teams removed the surface layer of damaged concrete and then shotcreted the replacement concrete containing migrating corrosion inhibitors. This helps protect against the insipient ring anode effect, where the addition of new concrete can counter and productively encourage the spread of corrosion to adjacent concrete. District 11 also used shotcrete with a migrating corrosion inhibiting admixture on some of the supports of the Fig. 3: A normal set version (version used with shotcrete) of an amine carboxylate migrating corrosion inhibitor admixture (ACCI) showed significantly higher corrosion protection under modified ASTM G109 cracked beam testing, an accelerated but more intense version of ASTM G109 saltwater ponding Image courtesy of Cortec Corporation Fig. 4: Liberty Tunnel before repair Photo by Dennis Bittner Rankin Bridge in Pittsburgh. The crew repaired damaged areas with shotcrete and applied a finish coat to the entire Fig. 5: Liberty Tunnel finished section Photo by Dennis Bittner www.shotcrete.org Summer 2017 | Shotcrete 13


2017SummerShotcreteEMag
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