Epoxy-resin coating and galvanization are direct methods for preventing the corrosion of reinforcing steel bar as for reinforcing-steel concrete structures. However, these methods costs more than regular reinforcing steels; therefore, reasonable, simple and highly effective anticorrosion methods are being developed.

One method to prevent the corrosion of precious metals and highly reactive metals is to confer water repellency by surface modification of reinforcing steel bar using self-assembled monolayers (SAMs). Surface modification using SAMs is a simple method in which metals are just immersed in a solution containing functional molecules. Therefore, such surface modification come to be great advantage for civil structures that use a lot of reinforcing steel. In this study, we aimed to apply SAM-based anticorrosion techniques to reinforcing steels.

To confirm the anticorrosion performance of SAMs on reinforcing steel bar, we evaluated the following anticorrosion properties: 1) corrosion protection performance confirmed through accelerated deterioration tests that replicate alkaline environments and salt-damage environments, and 2) corrosion protection performance confirmed through electrochemical measurements.

Figure 1 shows the results of accelerated deterioration tests involving a cycle of dry and humid conditions. The test specimens with SAM-modified surfaces showed no corrosion in the alkaline environment, but showed corrosion at the first cycle in the salt-damage environment.

Based on measurements of corrosion speed of the test specimens immersed in seawater (Figure 2), we investigated the effects of SAM on corrosion speed. The results showed that corrosion is faster in the following order: no SAM > SAM No. 1 > SAM No. 2 > SAM No. 3 > SAM No. 4. Therefore, we found that corrosion is slower than with no SAM when surfaces are treated with SAMs in the presence of corrosion. Accordingly, these results indicated that surface modification with SAM can reduce corrosion speed compared with regular reinforcing steels.

In future studies, we need to investigate the durability of SAMs and actual anticorrosion effects by burying test specimens with SAM-modified surfaces in concrete.