Fillers in cement and concrete are fine particles used to enhance the properties of the concrete mix. These can include materials such as fly ash, silica fume, slag, limestone, and other mineral powders. Fillers primarily function by occupying the spaces between the coarser aggregates, thus reducing the void content and enhancing the particle packing density of the mix. This improvement in particle packing contributes to a reduction in water demand, increased density, and enhanced strength. Additionally, some fillers, such as fly ash and silica fume, participate in the hydration process, forming additional cementitious materials that can further improve the strength and durability of concrete.