Case Study of the Performance of Prestressed Concrete Cylinder Pipes in the Greater Agadir of Morocco

Abstract

Prestressed concrete cylinder pipes (PCCPs) are widely used for water mains and wastewater lines that serve almost every major city in Morocco. By all accounts, PCCPs have performed relatively well over the years. However, in 2016, the Agadir Authority found failures due to widespread corrosion of the prestressing wires and water hammer damage. The failure rates were particularly severe in the case of the water transmission pipeline P3. Therefore, the objective of this study is to establish the main causes of the severe deterioration of the PCCPs used for the P3 pipeline project. To achieve this objective, a diagnostic study, both in situ and laboratory tests, were carried out to locate and visually inspect the damaged areas as well as to characterize the damaged PCCPs and the soil. The findings indicate that chloride-induced corrosion of the prestressing wires is the main cause of the PCCP failures. The high concentration of chloride ions in the mortar coating capillary system is found to originate from the soil and contamination of the PCCP mortar coatings. It is also found that the cyclical wetting and drying conditions coupled with the presence of high sulfate ions in the soil played a significant role in increasing the rate of corrosion. The low soil resistivity in areas between SP2 and Bouargane tanks tends to confirm that the PCCPs were damaged by the water hammer effect. Manufacturing defects (such as irregular mortar coating thickness, inconsistent prestressing wire spacing, and low quality of mortar) also significantly affect the performance of PCCPs. Based on the results obtained, the durability exposure class for the Greater Agadir was identified both as XA2 (i.e., moderately aggressive chemical environment) and XD3 (i.e., corrosion induced by chlorides other than from seawater) based on NM 10.1.008 and EN 206-1. In such exposure conditions, it is essential to use chloride or sulfate-resisting cement. However, the mortar coatings evaluated were neither sulfate resistant nor chloride resistant, therefore, the study concludes that the PCCPs installed were not adequately designed for the hazardous exposure conditions in the Greater Agadir region.