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39 NACE INTERNATIONAL: VOL. 55, NO. 10 MATERIALS PERFORMANCE OCTOBER 2016 tion, t ini , can be estimated for the two con- cretes. In the reference concrete, corrosion initiated at approximately eight to nine years of exposure. In the concrete contain- ing the corrosion-inhibiting admixture, 18 years of exposure may be considered a con- servative estimate for the time to corrosion initiation. The chloride content at the reinforcing steel mat's cover depth (15 mm) at t ini is de- fined as the critical chloride content C crit . 15 For the reference concrete, C crit is estimated at 0.10% chloride by weight of concrete (~0.7% by weight of cement); and for the concrete with inhibitor, C crit is estimated at 0.11% chloride by weight of concrete (~0.8% by weight of cement). Thus, the difference in C crit for the concrete with and without the corrosion-inhibiting admixture is sur- prisingly small. The present results allow only a conservative estimate of C crit for the case of inhi bitor -c ontaining c oncret e, which is 10% higher than the reference con- crete. Figure 4 show s that in order to achieve a chloride concentration that ex- ceeds C crit , considerably longer exposure time would be required for the inhibited concrete to initiate corrosion than the ref- erence concrete, and that delay is primarily associated with a reduction of the chloride diffusion rate. Having in mind that some tiny spots of corrosion were observed on th e reinforcin g st eel in th e inhi bitor - containing concrete after 18 years, it is un- likely that t ini will be much higher. Figure 4 also shows a first-hand, esti- mated extrapolation of the present results for cover depths greater than the present 15 mm. For instance, t ini becomes 40 years in the reference concrete and 80 years in the inhibitor-containing concrete with a cover depth of 25 mm . In short, t ini i s roughly doubled in the inhibitor-contain- ing concrete compared to the reference concrete. This beneficial effect is attrib- uted to the combination of the influences on chloride transport properties and on C crit . While both effects are relatively small, their combination appears to significantly prolong the service life in the presence of the corrosion-inhibiting admixture. Both investigated concretes performed well. When extrapolated to realistic cover depths in the range of 35 to 55 mm, t ini for the reference concrete is estimated to be close to or >100 years (Figure 4). A likely ex- planation for this desirable behavior may be the special care that was taken during execution (casting, compaction, curing, etc.) and the resulting good-quality con- crete. This highlights the importance of workmanship and careful execution on site for the durability performance of rein- forced concrete structures. Conclusions In the present long-term field trial, the studied organic corrosion-inhibiting ad- mixture (dosage 12 kg/m 3 ) was sufficient to significantly delay corrosion initiation in conditions with exposure to chloride- containing splash water. While corrosion initiated at a cover depth of 15 mm after approximately eight to nine years of expo- sure in the reference concrete, the concrete with the corrosion-inhibiting admixture was, after 18 years, still essentially corro- sion free. A chloride ingress model was used to extrapolate the results after 18 years of ex- posure for both deeper cover depths and longer exposure times. As a rule of thumb, under the studied conditions, the inhibitor delayed the time to corrosion initiation by a factor of two, which illustrates the poten- tial of this corrosion-inhibiting admixture to prolong the ser vice life of reinforced concrete. References 1 C.L. Page, V.T. Ngala, M.M. Page, "Corrosion Inhibitors in Concret e Repair Syst ems," Magazine of Concrete Research 52 (2000): pp. 25-37. 2 B. Elsener, U. Angst, Corrosion Inhibitors for Reinforced Concrete (Cambridge, U.K.: Wood- head Publishing, 2016). 3 T.A. Söylev, M.G. Richardson, "Corrosion Inhibitors for Steel in Concrete: State-of-the- Art Report," Construction and Building Mate- rials 22 (2008): pp. 609-622. 4 B. Elsener, M. Büchler, F. Stalder, H. Böhni, "Migrating Corrosion Inhibitor Blend for Reinforced Concrete: Part 1—Prevention of Corrosion," Corrosion 55 (1999): pp. 1,155- 1,163. 5 H . E . Ja m i l , M . F. Mo n t e m o r, R . B o u l i f , A. Shriri, M.G.S. Ferreira, "An Electrochemi- cal and Analytical Approach to the Inhibition Mechanism of an Amino-Alcohol-Based Cor- rosion Inhibitor for Reinforced Concrete," Electrochim. Acta 48 (2003): pp. 3,509-3,518. FIGURE 4 Projected chloride content in the concrete over time for (a) the reference concrete and (b) the concrete with the corrosion-inhibiting admixture. Different cover depths—15, 25, 35, 45, and 55 mm as indicated by the numbers on the lines—are plotted. The dashed blue lines represent the estimated chloride threshold values. Continued on page 40 Long-Term Field Performance of an Organic Corrosion Inhibitor for Reinforced Concrete