The ability of mineral fiber to act as a reinforcement and viscosity regulator is mainly dependent upon the fiber's diameter, length and amount added to the bitumen. Experience has shown that diameters of 4-6 microns and lengths of about 500 microns seem to be optimal with mineral fibers. Very thin fibers break easily and will result in very short fibers. Very short fibers give less increase in viscosity. Very thick fibers require an increase in the amount of fibers used and very long fibers tend to cause mixing problems. Fiberand mineral fibers have a mean diameter of 5 microns and this diameter remains constant irrespective of handling. The average fiber length will be shortened during handling in asphalt mix production. Fiberand thus supplies fibers of greater length than above mentioned in order to insure enough length to achieve the expected viscosity increase once the fibers are incorporated into the bitumen.

Mineral fibers contain certain amounts of unfiberized, coarse material (shot). The shot content thus influences the amount of fibers which are actually added to the asphalt mix.

The suitability of a mineral fiber for use in road asphalt is thus dependent on three criteria:

1. average fiber diameter
2. average fiber length
3. average shot content

These properties are controlled by the supplier and are part of the product specifications for Fiberand Mineral Road Fibers.