Service Life of Culverts (2015) / Chapter Skim
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8 CHAPTER THREE DEGRADATION MECHANISMS This chapter summarizes the degradation mechanisms that cause deterioration in the serviceability of culvert pipes over time. The environmental, structural, and hydraulic loading conditions that lead to degradation are also addressed.
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9 pH pH is a measure of a solution's acidity or alkalinity. It is a measure of the concentration of hydronium ions in solution, and ranges from 0 to 14.
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10 Resistivity values in excess of 2,000 to 5,000 ohm-cm (depending on the reference guideline) are generally considered to present limited corrosion potential (Table 1)
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11 Microbially Induced Corrosion Corrosion promoted or caused by microorganisms is known by a number of different terms, including; microbially induced corrosion, microbial corrosion, bacterial corrosion, biocorrosion, and microbiologically influenced corrosion. The term microbially induced corrosion (MIC)
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12 paved. Ault and Ellor (2000)
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13 • Table 855.2A: Definitions of abrasion levels and corresponding material recommendations. • Table 855.2B: Bed-material size and estimate of nonscour velocities for different flow depths.
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14 it is zinc or another substance -- is worn away, exposure to lowresistivity or low-pH environments can dramatically shorten a steel culvert's life. Although aluminum culverts are occasionally specified to combat corrosion, plain aluminum is typically not recommended for abrasive environments since tests indicate that aluminum can abrade as much as three times faster than the rate of steel.
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15 tive" modulus of elasticity selected in accordance with the design life of the system (the longer the time period, the lower the modulus)
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16 tion incorporating material performance and test requirements to allow HDPE pipe materials to be given a default 100-year service life. The material requirements take into account the higher ambient temperatures present in Florida, but do not consider freeze-thaw issues and as such are somewhat regionally specific in their applicability and acceptance across North American transportation agencies.
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17 material, and rock fragments that are used to form the side slopes and embankments will frequently roll onto exposed pipe ends or penetrate the pipe's overlying cover or embedment soil. Temperature affects all pipe materials differently.
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18 Pipe–Headwall Connection Issues (Rotation, Settlement, Scour, etc.) Other types of drainage pipe system failures are difficult to predict and can include rotation, settlement or foundation failure of headwalls, and scour at inlet and outlet ends (Figures 17 and 18)
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