When incorporating a loose stabilizer, which is usually packed in shrink-wrapped bags, extra time is needed for dry mixing the stabilizer with aggregate. A bag of stabilizer is thrown into the pugmill when the filler is being batched, and then an extra period (about 3 seconds) of dry mixing the fibers with the aggregate follows. Because of this, they are released from the bag and evenly distributed in the mixture. The binder is batched onto the dispersed fibers and aggregates, and additional wet stage mixing time follows. Again, one should to remember that too long a dry mixing time could destroy loose fibers.
Figure 9.5 depicts one sequence of the batching of SMA constituents into the pugmill with the use of a loose stabilizer. An example of another batching sequence is shown in Figure 9.6.
The NAPA SMA Guidelines QIS 122 recommend increasing the dry mixing time by 5-15 seconds in comparison with other mixtures without stabilizers. The wet mixing time should be increased by a minimum of 5 seconds when cellulose fibers are used and by not more than 5 seconds when mineral fibers are used.
