3.2.4.1 Commercially Produced Fillers (Added Fillers)
According to European terminology,! added fillers are made by crushing stone to produce fillers aimed at use in highway engineering. For a long time, the most popular of these has been, and is likely to remain, limestone filler. Limestone filler is distinguished by its affinity with binder, which is one of its strong points. Therefore in Europe limestone filler is most often used for SMA.
The other important feature of industrially manufactured fillers is their repeatability and uniformity of parameters. Finally it is worth observing their constant and repeatable mineralogical composition.
The use of fly ashes as fillers for SMA is uncommon. Their disadvantages include large specific area (fly ashes are very fine) and the spherical shape of the grains. So fly ashes have only been used to a limited extent and always need an engineering assessment before use.
The density of fly ashes is lower than that of crushed rocks or baghouse fines and fluctuates between 2.0 and 2.6 g/cm3. To obtain a similar volume share in a mineral
blend, ashes are metered in at a lower weight than a standard filler. The modified Rigden void content is usually less than 50% (Report FHWA-IF-03-019, 2003).
