Cathodic Protection Criteria for Prestressed Concrete Pipe-An Update

Prestressed concrete cylinder pipe is used in water and wastewater systems that serve virtually every major city in North America. Under certain conditions, such as high chloride environments, steel elements can depassivate, leading to corrosion. Under these conditions, cathodic protection (CP) can be used to protect the encased steel elements. This article provides the results of investigations performed during the past decade to determine the effects of CP on the performance of passivated, corroded, and split prestressing wire immersed in an environment to simulate sound mortar and mortar surrounding severely corroded wire. The current densities required to achieve a 100 mV polarization or depolarization shift and the maximum potential criterion to prevent hydrogen embrittlement (HE) were determined. Also determined were the effect of low pH caused by corroding wire, the susceptibility of prestressing wire to HE, and the approximate length of time and potentials to produce HE and eventual wire failure. The effect of discontinuing high levels of CP on the diffusion of hydrogen from wire and the recovery of ductility were evaluated.