Electron Probe Microanalysis Investigation into High-Volume Fly Ash Mortars

High-volume fly ash (HVFA) concrete has been widely investigated because of its lower carbon footprint and higher performance than the conventional portland cement concrete. In this work, a total of 21 HVFA mortar mixtures were fabricated using Class C fly ash, limestone powder, asphalt emulsion, and portland cement following a Box-Wilson central composite design scheme. The compressive strength and spitting tensile strength of these mortar specimens were tested at various ages. Based on the results of mechanical test, three representative mixtures were selected for water sorptivity test, surface resistivity test, and electron probe microanalyzer (EPMA) study. HVFA mortars with higher fly ash replacement and higher water to binder (w/b) ratio exhibited higher water absorptivity and lower surface resistivity. With secondary electron imaging (SEI) and back-scattered electron imaging (BSE), the micrographs of three selected HVFA mortars were examined, while the hydration behavior of fly ash particles in them was elucidated through the element mapping and element ratio mapping enabled by EPMA.