Effects of Fly Ash and Simulation of the Natural Hot and Dry Climate of the Moroccan Desert Region on the Durability of Prestressed Concrete Cylinder Pipes

The National Office of Water (ONEE) in Morocco reports that a many of the prestressed reinforced concrete pipes (PCCP) used to supply potable water in the semiarid region of the country have been deteriorating due to the corrosion of the prestressed wires. Moreover, in some cases, the PCCP degradation occurs within 1 year, which is typically less than their durability expectancy. This rapid development of corrosion in PCCP is due to the aggressiveness of the soil and also partly as a result of the cyclical wetting and drying exposure conditions in the region. In this study, the beneficial effects of fly ash (FA) incorporated in the mortar coatings of PCCP exposed to simulated aggressive soil (Errachidia soil) are evaluated. Two mortar coating mixes, F1 (0% of FA) and F2 (17% of FA), have been studied. The reinforced specimens were evaluated over a prolonged period of aggressive soil attack under 16 wetting drying cycles in the laboratory oven. The electrochemical techniques open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) made it possible to assess the protective capacity of the two mortar coatings. In addition, scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) analyses were performed to examine the microstructure of mortar coating. The results indicate that the incorporation of FA in the mortar coating under wet/dry cycling increases their resistance. This is confirmed by the stability of the OCP in the area of uncertain corrosion probability and the increase in resistance of the mortar (Rm) and charge transfer resistance (Rdl), approximately 82% and 90%, respectively. Meanwhile, the control mortar Rm increased only by 27% and the Rdl declined by 62% from 0 cycles to 16 cycles. In addition, the results of SEM-EDS analysis, chloride ion penetration depth, and visual inspection were in agreement with the electrochemical results.