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<br />i ' <br /> <br /> <br />~ ' j <br /> <br /> <br />, . <br /> <br />, <br /> <br />Exhibit 30. Reinforcing steel exposed in concrete pipe <br />due to concrete deterioration. <br /> <br />b. Abrasion --Abrasion is the process of wearing down or grinding away the <br />surface material of culverts as water laden with sand, gravel, or stones flows <br />through a culvert. Abrasive forces increase as the velocity of the water <br />flowing through a culvert increases; for example, doubling the velocity of a <br />stream flow can cause the abrasive power to become approximately four-fold. <br /> <br />Often corrosion and abrasion operate together to produce far greater <br />deterioration jointly than would result from either alone. Abrasion can <br />accelerate corrosion by removing protective coatings and allowing water-borne <br />chemicals to come into contact with corrodible culvert materials. <br /> <br />3-4.1 Aggressive Soil and Water Conditions. <br /> <br />Certain soil and water conditions have been found to have a strong <br />relationship to accelerated culvert deterioration. These conditions are <br />referred to as "aggressive" or "hostile." The most significant conditions of <br />this type are: <br /> <br />a. pH Extremes--pH is a measure of the relative acidity or alkalinity of <br />water. A pH of 7.0 is neutral, values of less than 7.0 are acid, and values <br />of more than 7.0 are alkaline. For culvert purposes, soils or water having a <br />pH of 5.5 or less are strongly acid and those of B.5 or more are strongly <br />alkaline. <br /> <br />41 <br />