Mastic is the second largest component of stone matrix asphalt (SMA); it is approximately 20-25% by weight of the mixture and 30-35% by volume. About 35-40% (v/v) of the compacted coarse aggregates is made up of voids, and after filling the aggregate with mastic, 3% to 5% (v/v) of empty space will be left.
Mastic[9] consists of the following:
• Fine aggregate
• Filler
• Stabilizer (drainage inhibitor) in the form of fibers or other additives
• Bituminous binder
Filler and binder make up mortar. Blends of the fine fraction of the filler with binder act like binders and can be tested as a binder, but blends of the total filler and binder act more like a mixture and can be tested in that manner (e. g., BBR1- stiffness, resilient modulus, and tensile strength) (Brown and Cooley, 1999).
In the preceding chapter we discussed how coarse aggregate particles make up a skeleton. The task of the coarse aggregate skeleton is different from that of the mastic. The functions of mastic are as follows:
• Binding (sticking together) the coarse aggregate skeleton
• Lubricating the coarse grains during compaction and enabling a proper aggregate structure in a compacted surface course
• Sealing the layer, or filling the voids in the compacted aggregate structure to provide it with high durability and resistance to other external factors such as water or deicers
• Withstanding stresses caused by load and temperature
Figure 3.1 shows the close packing of fine (passive) aggregate among coarse (active) grains.
Now let us deal with the mastic components.
