What is a "filler" in asphalt mixtures?

The concept of "filler" in asphalt mixtures primarily refers to a fine material added to fill voids within the mixture. This addition serves several purposes, including improving the workability and stability of the asphalt mix. Fillers can enhance the overall mechanical properties, such as stiffness and durability, by optimizing the particle packing and reducing air voids, which can lead to increased resistance to deformation and improved performance under loading conditions.

Additionally, fillers can affect the rheological properties of the asphalt binder, which enhances the performance of the asphalt mix over its lifespan. Common filler materials can include mineral powders such as limestone, silica fume, or fly ash, which contribute to the overall quality and performance of the final asphalt product. This role distinguishes fillers from other components such as aggregates, binding agents, or specific additives that serve different functions in the mixture.