Granulated products (Figure 4.6a and b) are produced by coating fibers with a binder or other binder-soluble agents. A binder coating enables control of the forces on fibers during granulation and separation of individual fibers, which is necessary for distributing them evenly in an SMA mix.
The granulated form of these products makes dosage at production easy. The fiber granules are supplied in big-bags or autotankers and are stored in the bags or silos. Automatic loading with screw-pneumatic feeders is also possible.
Special attention should be paid during the preparation of laboratory samples. Due to compression of the granules during production, a higher shear force is needed to distribute the fibers; therefore one should use a mechanical mixer. If samples must be mixed by hand, it is recommended to warm the granulated product in an oven to a temperature above the softening point of the coating agent. Otherwise the stabilizer will not work effectively in laboratory samples, possibly leading to unrealistically high-binder draindown.
Granulated products are the best options for SMA production at medium and large-capacity asphalt plants because of the ease of handling.
4.2.1.1 Granulated Cellulose Fibers with Additives
Several mixtures of cellulose fibers and various modifiers are also available. These types of compounds have been produced with two goals in mind—binder stabilization and a change in the specific characteristics of a mix (e. g., workability or durability). These compositions enable the simultaneous feeding of mixtures with fibers and additive. The effectiveness of such products should be tested in the laboratory to confirm the final properties of the asphalt mixture.
