Development of a sustainable acid resistant mortar for back-filling of impressed current cathodic protection (ICCP) anodes

Abstract

Reinforced concrete (RC) structures in marine environments are highly susceptible to chloride-induced corrosion, for which impressed current cathodic protection (ICCP) is widely applied. The performance of ICCP systems is governed by the durability and electrochemical behaviour of the anode back-fill mortar. Field observations from New South Wales, Australia, show that conventional Portland cement-based mortars can degrade due to electrochemically induced acidification at the anode interface, highlighting the need for more stable and compatible materials.

This thesis investigates ICCP-induced acidification through field sampling, laboratory characterisation, and electrochemical testing. Analyses of mortars retrieved from operational marine bridges show that anodic reactions generate acidic species that dissolve calcium-rich phases, promote gypsum formation, and degrade the binder, resulting in non-uniform deterioration. These mechanisms were reproduced under accelerated laboratory conditions.

Based on this understanding, hybrid geopolymer mortars incorporating supplementary cementitious materials (SCMs) were developed as acid resistant alternatives. Laboratory results show improved resistance to acidic exposure, reduced mass loss, and enhanced microstructural stability. Field implementation confirmed material integrity and compatibility with electrochemical requirements under marine exposure.

Transport properties were also assessed. While higher SCM content improved durability, it increased resistivity, highlighting a trade-off between durability and electrochemical performance. Ionic conductivity governed polarisation behaviour, and its optimisation improved performance in atmospheric zones, while conductive additives were unnecessary in submerged conditions.

Overall, this research establishes an exposure-specific framework for designing ICCP back-fill mortars that balance durability and electrochemical functionality in marine environments.