If porous spots are not visible around the fat spot, this is not a case of classic segregation. We may suppose that the fat spot appeared because of an excess of mastic volume (an error of design). It may also have been caused by too much energy applied during compaction (improperly adjusted or unskillfully applied vibration); this will lead to the crushing of the coarse aggregate skeleton and the squeezing out of the mastic. Then the surface with the bleeding mastic will make up a major part of the surface (which, simply put, is any area where bad compaction was applied). A related problem, described in Section 11.5, describes an SMA surface that is too closed or tight.
Small fat spots with a circular shape of approximately 3-20 cm in diameter may appear on a laid SMA course, randomly scattered without any visible order of occurrence (Figures 11.4 and 11.5). This type of fat spot hardly ever appears. As usual, their composition should be checked. Most often, mastic and stabilizer (especially loose fibers) can be found in them. They are most often caused by insufficient mixing of the SMA components (i. e., insufficient wet-mixing time at the mixing plant).
