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<br />maintainability, durability, and total costs. Some of the design features <br />which can increase durability are: <br /> <br />a. Selection of Culvert Materia1s--some materials can be expected to <br />perform better than others under any given set of conditions. Each agency <br />should carefully investigate the soil and water conditions that affect culvert <br />durability in its jurisdiction and develop meaningful guidelines to aid in the <br />selection of culvert materials. <br /> <br />Special attention should also be given to standards and specifications used at <br />the time of the culvert's installation,. Changes in gauge thickness and <br />chemical composition of metal pipes, or cement content and steel reinforcement <br />for concrete pipes, may affect the durability of the pipe. The following <br />guidelines reflect common durability characteristics observed on culverts <br />installed prior to 19B3. <br /> <br />(1) Galvanized Steel. Bare, uncoated, galvanized steel pipe generally <br />performs well when the pH of the soil immediately adjacent to the <br />pipe and the pH of the flow which the pipe will carry are between <br />6 and 10 and when the electrical resistivity of the soil is 3,000 <br />ohm-cm or greater. Bare galvanized steel pipe should not be used in <br />salt or brackish environments. <br /> <br />(2) Aluminum. Bare, uncoated, aluminum alloy pipe generally performs <br />adequately well when the pH of the soil immediately adjacent to the <br />pipe and the pH of the flow which the pipe will carry are between 4 <br />and 9, and when the electrical resistivity of the flow and the <br />minimum electrical resistivity of the soil are 500 ohm-cm or <br />greater. When backfilled with a clean, granular, well-draining soil, <br />aluminum pipe has shown excellent resistance to corrosion even when <br />exposed to seawater and tidal flow. Aluminum may not perform well in <br />very acid or heavy metal (copper, iron, etc.) environments. <br /> <br />(3) Concrete. Concrete of good quality is resistant to many corrosive <br />agents. When the effluent has a pH of 5.0 or less, protective <br />measures are generally required. <br /> <br />(4) Other Materials. Very aggressive environments may require special <br />pipe materials such as vitrified clay, stainless steel, and plastic. <br />These materials are generally used in culvert applications only when <br />detailed analysis indicates the potential for serious durability <br />problems. <br /> <br />b. pipe Protective Measuresn-lhere are severa) <br />be taken to increase the durability of culverts. <br />measures are: <br /> <br />protective measures that can <br />The more commonly used <br /> <br />(1) Extra Thickness. For some aggressive environments, it may be <br />economical to provide extra thicknesses of concrete or metal. <br /> <br />43 <br />