Finely ground mineral powders are often used to replace cement in the binder phase.Such fillers, are known to accelerate cement hydration rates.This "filler effect" has been often attributed to the effects of dilution (i.e., w/c increase as the cement content is reduced), or the provision of additional surface area by fine filler powders.The surface area increase is speculated to provide additional nucleation sites for hydration products, thereby accelerating reactions.This study examines the influence of filler content, surface area, and mineral type (i.e.quartz or limestone) on cement reaction rates using both experimental and computational techniques.Original simulations carried out within a phase boundary nucleation and growth (BNG) model indicate that the extent of acceleration is linked to the magnitude of surface area increase, and the capacity of the fillers surface to offer favorable nucleation sites for hydration products.Simulations using a kinetic cellular automaton model (HydratiCA) indicate that the acceleration is linked to a fillers interfacial properties, which increase or decrease its tendency to serve as a nucleant, as well as to the composition of the filler, particularly relating to the ability of its ionic constituents to participate in ion-exchange reactions with the calcium-silicate-hydrate (C-S-H) phase.Observations from isothermal calorimetry are correlated with simulations, demonstrating that limestone is a superior filler to quartz at equivalent surface areas due to its preferred interfacial properties and its ability to participate in ion exchange reactions.This research provides a new basis for more comprehensive evaluations of filler agents, with the goal of increasing filler contents to reduce cement use, without compromising mechanical property development.