Corrosion in soil is a complex phenomenon, but there are some basic concepts that are useful in understanding the process. Underground corrosion is electrochemical in character, and this fact is used to describe the corrosion process in terms of an ordinary dry cell. The differences between corrosion in disturbed and undisturbed soil are discussed, and data are presented to emphasize these differences. The results reveal that soil composition is less important than soil resistivity, but both are subordinate in importance to oxygen availability. Thus, corrosion is negligible in undisturbed soils where oxygen concentration is low.

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The progress on a research program directed at developing a nondestructive method for measuring the corrosion of steel in concrete as related to bridge deck deterioration is reported.Several polarization techniques for measuring the corrosion rate of steel in concrete are correlated to actual weight loss measured gravimetrically. The design of a prototype automated minicomputer system for measuring the corrosion of steel in concrete is also described.Included are the results of a laboratory basic study on the effect of pH, Cl", On, and moisture on initiating and maintaining corrosion in mortar.