Materials Performance Supplements

CORTEC 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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MIGRATING CORROSION INHIBITORS range of the Bode plot. The diameter of the Nyquist plot is a measure of the Rp value. During this investigation, changes in the Rp and the corrosion potential of the rebar were monitored to ascertain the degree of effectiveness for these admixture products. The samples were tested on a weekly basis and the data were collected for analysis. Post experiment, visual obser vation scannin g el e ctron mi cro sc opy ( SE M)/ energy dispersive spectroscopy (EDS) anal- yses were conducted on the steel rebars. A large area surface x-ray photoelectron spec- troscopy (XPS) analysis was performed on several steel rebars removed from different concrete samples using XPS in electrostatic lens mode with a resolution pass energy of 80 eV and an aluminum monochromator anode. The depth profiles were conducted using argon ions at 4.0 kV. Results and Discussion Polarization resistance measurements of steel rebar in a 3.5% NaCl solution are shown in Figure 1. The amine carboxyl- ate-based MCIs increased the Rp from 2,300 Ω.cm 2 to 31,000 Ω.cm 2 . There was successful corrosion inhibition of the steel rebar even in the presence of chloride when the admix- tures were added to the concrete. The con- trol sample and the sample with soda ash had decreasing polarization resistance. The steel rebars were not protected from corro- sion attack. EIS Bode plots for the steel rebar from the different concrete samples after 150 days immersion in 3.5% NaCl are shown in Figures 2 and 3. Polarization resistance measurements show an increasing trend (reduced corro- sion rate) for the samples with inhibitor, while the control and soda ash samples have an increasing corrosion rate. Inhibi- tor-protected samples showed an average c orrosion rat e of 0.28 µA/cm 2 (with a decreasing trend) compared to the EIS Bode plot results for untreated samples showing a rate of 5.5 µA/cm 2 . This reduc- tion of the corrosion rate translates to an increase in the life expectancy by more than 50 to 60 years (Table 1). The steel rebar sur- face conditions after 150 days of testing are shown in Figure 4. XPS analysis confirmed the presence of the amine carboxylate-based inhibitor on the steel rebar surface. Depth profiling showed a 50-nm layer of amine-rich com- pounds and chloride ions on the rebar sur- face. Neutralizing effects of the inhibitor assured satisfactory corrosion resistance and the ability to passivate the steel rebar even in the presence of corrosive chloride ions. The XPS results established that both the admixtures and corrosive species (chlo- ride 1.60-2.20%) were present on the rebar surfaces (Figures 5 and 6). The corrosion inhibitors managed to coat the surface and neutralize the corrosive species (chloride ions) to protect the steel rebar. Conclusions Amino carboxylate-based corrosion inhibitors (admixtures) successfully demon- strated corrosion inhibition of rebar and can prolong the life of reinforced concrete struc- tures. Rp increased from 2,300 Ω.cm 2 to 31,000 Ω.cm 2 when admixtures were added to con- crete. The addition of soda ash to the con- crete mixture showed better corrosion pro- tection than for the untreated concrete sample; however, inferior results occurred to those of the concrete samples with corrosion inhibitors. Inhibitor -protected samples showed an average corrosion rate of 0.28 µA/ cm 2 (with a reduced trend) compared to untreated samples that measured 5.5 µA/cm 2 (based on EIS test results). This reduction in the corrosion rate will increase life expec- tancy by more than 50 to 60 years. Depth pro- filing showed a 50-nm layer of amine-rich compound and chloride ions on the rebar surface. XPS analysis confirmed the presence of the amino carboxylate-based inhibitor on the steel rebar surface. Neutralizing effects of the inhibitor assured satisfactory corrosion resistance even in the presence of 1.6-2.2% chloride ions. TABLE 1. LIFE EXPECTANCY PREDICTION BASED ON THE CORROSION OF THE STEEL REBAR IN CONCRETE Sample Rp (Ω.cm 2 ) Corrosion Rate (uA/cm 2 ) Life Expectancy (Years) Inhibitor A 39,400 0.28 >50 Inhibitor B 28,800 0.39 >50 Soda Ash 7,180 1.56 ~10-12 Control 2,030 5.51 ~5-6 FIGURE 4 Comparison of corrosion behavior for the steel rebar from different concrete samples after 150 days immersed in 3.5% NaCl solution shows localized corrosion attack and red rust for- mation on the control and soda ash samples. 22 JUNE 2018 MATERIALS PERFORMANCE CORTEC SUPPLEMENT TO MP

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