Characterization of steel corrosion in alkali-activated mortars using advanced techniques

Alkali-activated materials have emerged as a promising substitute for ordinary Portland cement (OPC) in various applications. This study explores the use of different monitoring techniques for assessing the long-term corrosion behavior of steel in alkali-activated mortars, which remains relatively understudied. Three types of alkali-activated mortars (AAMs) were prepared, based on fly ash, slag, or metakaolin as the precursor material. The corrosion of embedded steel was investigated under wetting and drying cycles with chloride-containing solution for up to one year. Two unconventional techniques were used to monitor corrosion: coupled multi-electrode array sensors (CMEA) to measure partial currents, and electrical resistance (ER) sensors to track thickness reduction. The ER sensors enabled evaluation of general corrosion rates over time, while CMEA provided insight into corrosion initiation and its spatiotemporal distribution. In addition, the corrosion damage on the embedded steel and sensors was evaluated using X-ray computed microtomography (microCT). Distinct corrosion patterns were observed depending on the precursor material: severe corrosion in metakaolin-based AAMs, localized pitting in slag-based AAMs, and moderate damage in fly ash-based AAMs. The study demonstrates the complementary value of CMEA and ER sensors and highlights the challenges of characterizing the long-term corrosion processes in these alternative binder systems • ER sensors monitored general corrosion rates of steel in AAMs over time. • CMEA detected corrosion initiation and spatiotemporal corrosion distribution. • Corrosion: severe in MK, pitting in slag, and moderate in FA-based AAMs.