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GEOTECHNICAL PROFESSIONALS, INC.August 15,1997 <br />MJS&A #97246 Page 2 <br />SOIL CORROSIVITY <br />A major factor in determining soil corrosivity is electrical resistivity. The electrical resistivity of a <br />soil is a measure of its resistance to the flow of electrical current. Corrosion of buried metal is an <br />electrochemical process in which the amount of metal loss due to corrosion is directly proportional <br />to the flow of electrical current (DC) from the metal into the soil. Corrosion currents, following <br />Ohm's Law, are inversely proportional to soil resistivity. Lower electrical resistivities result from <br />higher moisture and chemical contents and indicate corrosive soil. <br />A correlation between electrical resistivity and corrosivity toward ferrous metals is: <br />Soil Resistivity <br />in ohm-centimeters Corrosivity Category <br />over 10,000 mildly corrosive <br />2,000 to 10,000 moderately corrosive <br />1,000 to 2,000 corrosive <br />below 1,000 severely conosive <br />Other soil characteristics that may influence corrosivity towards metals are pH, chemical content, <br />soil types, aeration, anaerobic conditions, and site drainage. <br />Electrical resistivities were in corrosive and severely corrosive categories with as-received moisture <br />and at saturation. Some as-received resistivities were at or near their saturated values. <br />Soil pH values varied from 7.3 to 7.6. This range is neutral to mildy alkaline and does not <br />particularly increase soil corrosivity. <br />The chemical content was very high in the sample B-1 @ 25' and less in the others. Sodium sulfate- <br />was the predominant compound. The level of sulfate exposure in the deep soil is severe per the <br />Uniform Building Code (UBC) or American Concrete Institute (ACI-318). This probably applies <br />to all soil below the water table and possibly above. The 2 foot deep soil has a moderate sulfate <br />exposure. <br />Sulfide, which is aggressive to copper and ferrous metals, showed no reaction in a qualitative test. <br />The positive redox potential indicates oxidizing conditions in which anaerobic, sulfide producing <br />bacteria are inactive. <br />This soil is classified as severely corrosive to ferrous metals, and deleterious to concrete.