Effect of particle packing and fly ash on performance of ordinary Portland cement/anhydrite-activated ground-granulated blast-furnace slag

A common practice 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, which is an economical and low-cost procedure. However, problems with activation arise that lead to low strength development, especially at an early age. This paper is focused on the influence of optimizing particle packing, which would decrease the cement/aggregate ratio while optimizing the space in the cement matrix; and on the effect of different fly ashes on the strength development of ordinary portland cement (OPC)/anhydrite-activated ground-granulated blast-furnace slag (GGBFS) cement. The optimized particle packing demonstrated to have a significant impact on the mechanical properties, both at early and late compressive strengths, compared with the nonpacking compositions. Substitution of fly ash for ultrafine aggregates significantly affected the mechanical properties, as well as the hydrates formed during the hydration process, depending on the fly ash properties.