Fat spots in wheel paths appear at the time of SMA pavement trafficking. They are located in the paths of vehicle wheels and can run up to several hundred meters (possibly including the whole SMA wearing course of a road) (Figure 11.34).
We have to go back to the chapter on designing an SMA mixture and the volume relations taking place in it to explain causes of the appearance of such “sweating offs” of mastic in the wheel paths. Recall that some air voids for mastic are intentionally left in a compacted and interlocked coarse aggregate skeleton. Additional compaction of a course under tires causes a closer arrangement of the coarse aggregate grains during trafficking. This reduces the volume of free space designed for mastic, and consequently the mastic is squeezed-out onto the surface. In some cases, this phenomenon confirms the Dutch idea about the enlarging effect and the need to design SMA with a bit higher void content (see Chapter 7).
Another reason for the occurrence of such a phenomenon is opening the pavement to traffic too early. Loads on an SMA that is still warm can destroy this mixture in a short time.
