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Acceleration of Fe Corrosion in Cement Paste and Mortar By Enhancing Oxygen Supply

Monday, 2 October 2017: 08:50
Camellia 2 (Gaylord National Resort and Convention Center)
K. Doi, S. Hiromoto (National Institute for Materials Science), and E. Akiyama (Tohoku University)
Generally, in concrete, alkalinity of the environment is maintained and reinforcing steels exhibit superior corrosion resistance owing to passive film. Therefore, it is difficult to demonstrate Fe corrosion in concrete in the laboratory in a short time. A new method for acceleration of Fe corrosion is necessary.

Recently, some researchers tried to accelerate the Fe corrosion in concrete. They accelerated Fe corrosion by anodic polarization and cyclic corrosion test. In this study, an accelerated corrosion test method with enhancing oxygen supply was developed to enhance oxygen reduction on Fe surface and Fe corrosion in concrete. The effect of amount of oxygen supply on Fe corrosion in cement paste and mortar will be discussed in our presentation.

The sample was 99.5% Fe sheet with 7×7 mm2and 1 mm thickness. The Fe sample was embedded in cement paste or mortar with 5 mm cover thickness and cured for 28 days. In order to prompt breakdown of passive film on the Fe sample, 2.06 M NaCl solution was mixed to the cement paste and mortar. Fig. 1 shows the schematic image of Hyperbaric-oxygen accelerated corrosion test we developed. In the gas pressure chamber, Fe in cement and Fe in mortar were immersed in 2.06 M NaCl solution under the pressured oxygen of 0.5 or 2.0 MPa for 14 days. For comparison, corrosion of Fe in cement and Fe in mortar immersed in the NaCl solution under ambient air was also discussed. After finishing the immersion under pressured oxygen or ambient air, surface and cross section of Fe sample were observed using an optical microscope and SEM. In addition, composition of the rust on Fe sample was analyzed using Raman spectroscopy measurement.

Corrosion of the Fe in cement and Fe in mortar was obviously accelerated under the pressured oxygen of 0.5 MPa, and the corrosion of Fe in mortar was further enhanced than that of Fe in cement. Composition of the rust formed under the pressured oxygen of 0.5 MPa was similar to those formed in the real environment. It is thus demonstrated that the enhancement of oxygen supply is beneficial and effective to validly accelerate Fe corrosion in concrete.

Corrosion of the Fe in cement and Fe in mortar was suppressed under the pressured oxygen of 2.0 MPa compared to corrosion under the pressured oxygen of 0.5 MPa. It is considered that corrosion of Fe in cement and Fe in mortar is dominated by oxygen reduction reaction under the pressured oxygen of 0.5 MPa, while the excess oxygen makes passive films more protective and corrosion of Fe is suppressed under the pressured oxygen of 2.0 MPa.