AbstractThis paper discusses the main causes of the severe deterioration of prestressed concrete cylinder pipes (PCCPs) used for potable water distribution in northeastern Morocco. A diagnostic study and in situ and laboratory tests were performed to gain some insight into the causes of the deterioration of PCCPs. Overall, it was found that the failure of PCCPs in the region is primarily the result of improper pipe joint installations, which allow water to leak from the pipes, allowing chlorides in the mortar coating to reach the prestressing wires inside the pipes and causing their corrosion. The mortar used to spray the prestressing wires was found to have been contaminated with chlorides during mixing by way of the mixing water, sand, and/or aggregates. The presence of sulfate ions in the mortar coating and the cyclical wetting and drying conditions of the region further accelerated corrosion rates. It was also found that poor bedding of pipes in the region’s marl soil resulted in differential settlement, causing high stress at joints, leading to cracking of the mortar coatings and corrosion of the prestressing wires and cylinders. The soil surrounding the pipes was, however, not found to be aggressive and there was no groundwater (at the buried depth of the PCCPs of approximately 2 m). The overall durability exposure class for the region was identified both as “cyclic wet and dry” and “moderately aggressive chemical environment” according to the Moroccan and European concrete standards.