In the majority of worldwide regulations for SMA, the content of particles passing through the smallest sieve (0.075 or 0.063 mm ) generally ranges between 8% to 13% (m/m). However, adopting extreme quantities may be a risky business—that is, 8% can lead to building too little mastic. On the other hand, a large quantity of filler (e. g., approximately 13%) may generate too high a content of mastic, making it susceptible to overstiffening or increasing the risk of forming fat spots.
It has been discussed in Chapter 3 that the optimum relationship between quantities of filler and binder is best illustrated by the filler-to-binder ratio (by weight or volume). This means that each quantity of filler corresponds to a certain optimum amount of binder. The details behind this assumption are inexact, resulting perhaps from experience with a run-of-the-mill filler in a given country. After reading Chapter 3, it should be clear that there are all sorts of fillers and the differences between them do not lie only in one specific area (e. g., gradation, degree of grinding) but also in the different content of voids in the compacted filler (determined using Rigden’s method).
