Almost every working road laboratory has conducted many series of draindown tests. The results of companion tests on a wide variety of stabilizers are seldom published. However, the following interesting conclusions can be drawn from large — scale research conducted in the United States (Brown and Mallick, 1994):
• SMA binder draindown was seen to be a time-progressive process; the fastest run-off occurred within the first 30 minutes of hot mix storage, then it continued over 2 hours during testing. Therefore one can conclude that the major part of the draindown process takes place during the 1st hour after SMA production.
• The most effective stabilizers tested were cellulose and mineral fibers.
• Differences between binder-absorbing stabilizers and viscosity-enhancing stablizers were observed.
• Lack of a stabilizer caused as much as 4% (m/m) mastic drain-off in a 0/19 mm coarse-graded SMA.
During the course of a season of roadwork, we decide, for various reasons, to change the supplier of stabilizers, but we do not always have enough time to check the SMA draindown with the new product (after all, it looks more or less the same). At that time, we have to take into account some unexpected problems and be prepared to react quickly—for example, to increase the quantity of stabilizer, if needed.
JMF — Job Mix Formula — recipe of the mixture.
