No matter the method applied when designing the SMA composition, the first step that must be taken is establishing the maximum particle size in the aggregate mix. The following factors should be taken into account when considering this issue: [23]
6.1.1 In Which Course?
Due to the outstanding performance of SMAs in surface courses, they have also been used in intermediate courses (e. g., in the United States, Australia, and recently Germany). Normally mixtures with larger maximum particle sizes (e. g., 0/19 or 0/22 mm) are selected for that purpose when they are permitted by local regulations. So far, aside from possible economic obstacles (high cost), it has not been stated that SMA is unfit to be used in intermediate courses. Consequently, if one can afford to and knows how to design and execute SMA intermediate courses, why not dare to?
When using SMA as a course on a bridge deck, the gradation should be selected rather conservatively (i. e., it should be finer). The composition of the asphalt mixture should also be designed with great care and mostly with the use of the type of polymer modified binders that increase the fatigue life of an asphalt mix. (See Chapter 13 for further discussion of SMA for bridge decks.)
