Nanoindentation and SEM/EDX characterization of the geopolymer-to-steel interfacial transition zone for a reactive porcelain enamel coating

The increasing use of alternative cementitious materials such as geopolymers as an environmentally-friendly alternative to traditional cements requires an improved understanding of the interfacial transition zone (ITZ) between the matrix and reinforcing steels. In this study, nanoindentation measurements were spatially coupled to images with scanning electron microscopy and chemical composition using energy dispersive X-ray microanalysis. The study focused on the microstructure and chemical composition of the interfacial transition zone (ITZ) for reinforcing steel embedded in a geopolymer mortar. The ITZ was analyzed for uncoated steel and steel coated with a reactive porcelain enamel that improves bonding and corrosion resistance. Results indicate that a more gradual transition of mechanical properties and chemical composition for the coated steel coupled with improved integration to the mortar correlates to increased bond strength measured in macroscale experiments.