A study of potential methods for controlling macro-cell corrosion of buried steel pipes in concrete/Soil systems by the addition of uric acid as a concrete admixtures

Severe localized corrosion of steel pipes, buried in concrete/soil systems (known as macro-cell corrosion), is induced by cathodic reactions on those steel surfaces that are located in the concrete, accompanied by anodic reactions (i.e., corrosion) on those surfaces that are located in the soil. The addition of cathodic inhibitors to the concrete, in the form of cement admixtures, is therefore expected to be an effective means of suppressing this phenomenon. Concrete test specimens (ordinary Portland cement; water/cement ratio: 61%), containing uric acid as the inhibitor have been formulated and the inhibitory effect of uric acid on the macro-cell corrosion has been examined by the measurement, over 862 days, of the currents flowing between the steel (SGP) pipes embedded in the concrete test specimens and those buried in soil. Dry mixing of 10% uric acid by weight was shown to decrease the currents, which indicates that macro-cell corrosion can be effectively controlled by uric acid. Addition of 0.3 or 3% uric acid was ineffective. This tendency was also supported by the results of weight-loss measurements of steel pipes buried in soil. The inhibitory effect becomes more predominant as the measurement time increases (inhibition efficiencies: 64% for 0-862 days, 78-91% for 297-862days).