Long‑term phase changes in cathodically protected marine reinforced concrete bridge

Abstract

The application of cathodic protection (CP) gains increasing interest for maintaining the structural integrity of coastal concrete bridges facing premature degradation due to reinforcement corrosion. The present investigation was undertaken to obtain field experience on the long-term performance of impressed current cathodic protection (ICCP) installed on a Norwegian marine concrete bridge. Cores with and without anode ribbons from five protection zones were extracted 16–17 years after installation of ICCP. The cores were investigated by visual inspection and using µ-XRF for elemental distribution. µ-XRF measurements showed decreased intensities for calcium and sulfur around anode ribbons in some samples. Chloride accumulation at anode ribbons was observed in three of five cores, leading to lower ingress depth in the concrete but also a higher maximum chloride content near the anode compared to the cores without anode ribbons. The anode ribbons appeared intact. Phase changes around the anode ribbon were investigated with XRD, TGA and pH measurement. The ICCP had induced neutralization (pH 7) of the overlay mortar in the vicinity of some of the anode ribbons, resulting in the decomposition of hydration products like portlandite and the formation of gypsum, leading to a weaker material.