Acid Corrosion of Reinforced Concrete Pipes - The Buried Facts
Annual Conference
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Acid corrosion of concrete pipes is a well documented degradation mechanism for this product which is used as a vital component of New Zealand’s infrastructure. This paper will review and update the various acid attack mechanisms that are common to the industry and outline design solutions accordingly. All acid attack mechanisms are not equal and are often confused in this regard with the provision of sulfate resistance. The paper will clarify these issues.
The mechanism of biogenic sulphuric acid attack, which may occur in concrete sewer pipes, will be reviewed, and the work carried out in the USA to understand the significant factors outlined. American EPA had published a design manual involves various equations that allow a design prediction of rate of sulphide built up in pipe networks, and estimation of concrete pipe wall attack rates. Simplified Excel modeling spreadsheet based on this design approach has been developed. Design examples presented in this paper indicate that well designed and maintained concrete pipelines could safely last for their nominated life; on the other hand, examples of some limited severe cases, indicate that protecting with inert PVC or PE lining, or active measures to reduce sulphide concentration may be needed.
New Zealand laboratory mineral sulphuric acid attack tests have been completed by various agencies and companies on pipe samples with different SCM. While positive laboratory results were achieved, site performance did not always meet the expectation. European research in this area has found that biogenic sulphuric acid attack has a different mechanism to mineral acid attack, therefore; laboratory and field behavior is quite different. Attempts in Europe to develop a field representative, bench-top, biogenic acid attack test will be presented.
Australian pipe companies, through the Australasian industry body, CPAA; have researched acid attack on pipes due to acidic soils and dissolved CO2 and developed methods to predict depth of attack for various acid concentrations and pipe age. Examples of utilizing the CPAA methods to provide design solutions to achieve 100 years design life in aggressive acidic soil and groundwater situations of major highway projects in NZ, will be presented.
Future solutions and methodologies to support the industry in this particular range of aggressive concrete pipe environments will complete the presentation.