Effect of fly ash particle packing on performance of OPC-activated GGBS slag

An important way to produce concrete with a lowered CO2 embodiment is to use high levels of supplemental cementitious materials (SCMs), such as slag and fly ash, in place of Portland cement. This paper is focused on the influence of fly ash on Portland cement (OPC)-activated GGBS cement, a very low OPC formulation. The study examined the effect of particle packing as well as the effect of fly ash on strength development. First the influence of fly ash on strength development on mortars with optimized particle size distribution and packing was conducted. Then, keeping the levels of the cementitious materials the same, mortars with non-ideal particle packing were studied. The mortar packing was optimized following the modified Andreassen model, demonstrated to have a significant impact on the mechanical properties, both at early and late compressive strengths of OPC-activated slag, compared with the non-packing compositions. Substitution of fly ash for fine aggregates significantly affected the mechanical properties depending on the class and particle shapes of the fly ash.