The term filler means an aggregate that mostly passes through a specified sieve (0.063 mm in Europe, 0.075 mm in the United States). It should be emphasized that the material just discussed, which is generally called filler, denotes all the grains—that is, both those coming from the added filler and those occurring on fine and coarse aggregate grains in the form of dust. Thus if we want to know the behavior of a filler fraction in a given mixture, then all the grains below a specified sieve size in a final mineral blend should be separated, regardless of their source. All that material should be tested. If we only test the added filler, the results do not show the influence of the entire filler fraction on the properties of the mix.
The significant influence of filler on asphalt mixtures may be defined in the following way (Anderson et al., 1982; Kandhal et al., 1998; Druschner, 2006): [11]
One could say that filler is the most underestimated component of SMA. After all, it constitutes from 8% to 12% of a mixture, which actually is a significant amount.
Next we will turn our attention to two concepts used in explaining the behavior of filler—the specific area of a filler and the content of voids in a compacted filler. These concepts can help describe various phenomena occurring in mixes.
