In general, most regulations and guidelines do not permit manually placing SMA mixtures; however, there are places where there is no other option but to place the mixture manually (e. g., small and irregular pieces of a roadway) (Figure 10.10). In such cases one should remember not to scatter the mixture with shovels but to carry and lay it down. Compaction should be carried out immediately after laying and alignment. Unfortunately such surfaces will differ in structure from adjacent areas spread mechanically, and usually they will be more porous and permeable.
Bearing in mind the unique philosophy of designing an SMA aggregate skeleton (see Chapters 2 and 6), SMA compaction may be regarded as the process of forming a structure made up of appropriately arranged and interlocked grains filled with mastic. While rolling, the mixture volume is reduced by the tighter arrangement of particles and a decrease in the content of air voids. The binder makes compacting easier. It plays the role of a lubricant, easing the movement of aggregate at that stage of an SMA’s performance.
10.4.1
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Types and Number of Rollers
The fact remains that SMA is a difficult mixture to compact, therefore the appropriate selection of both the number and type of rollers is of real significance.
