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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structures. Laboratory tests have proven that these corrosion inhibitors migrate through the concrete to protect the rebar against corrosion even in the presence of up to 2.20% chlorides. 9 Experimental Procedure This study focused on the usefulness of inhibitors based on amino carboxylate chemistry and their means of application. Six concrete samples were cast (dimensions 280 by 110 by 150 mm) per ASTM G109 12-13 using commercial-grade silica sand, Port- land cement, fly ash, and limestone (con- crete mixture ratio: 1 cement/2 fine aggre- gate/4 coarse aggregate). The reinforced concrete samples included one control, one with soda ash, and four with corrosion inhib- itor admixtures. Two inhibitors, A and B (both amine carboxylate-based), were added to the concrete mix per the ASTM G109 sam- ple preparation method, with reinforcement rebar placed at 20-mm concrete coverage. These samples were prepared with a 0.55 water/cement ratio. All samples contained three electrodes (class 60 steel rebar with dimensions of 300 mm length, 12.5 mm diameter). Concrete compressive strengths were roughly 26 MPa after 28 days of curing. The ASTM G180 14 test method involving steel and concrete admixtures was used to verify effectiveness of the corrosion inhibi- tors. The concrete samples were immersed in 3.5% sodium chloride (NaCl) at ambient temperatures and tested for a period of 150 days. The corrosion behavior of the steel rebar was monitored using electrochemical impedance spectroscopy (EIS). The experi- ments were conducted using commercially available systems for EIS and direct current corrosion tests. Bode plots were created from the data obtained using the potentio- static technique. By comparing the Bode plots, changes in the slopes of the curves were monitored as a means of establishing a trend in the resistance polarization (Rp) value over time. To verify this analysis, the Rp values were also estimated by using a curve-fitting algorithm on the Nyquist and Bode plots. In these plots, the Rp and RΩ combined values are displayed in the low frequency range of the Bode plot and the RΩ value can be seen in the high frequency FIGURE 1 Polarization resistance measurements of steel rebar in 3.5% NaCl solution. FIGURE 2 Comparison of the EIS Bode plots of steel rebar in different concrete mixes after 150 days of immersion testing. FIGURE 3 Polarization resistance measurements of steel rebar in concrete using EIS show an increasing trend (lowered corrosion rate) for the inhibitor, while control and soda ash samples have a decreasing trend (increased corrosion rate). 21 CORTEC SUPPLEMENT TO MP MATERIALS PERFORMANCE JUNE 2018

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