Various methods for testing the tendency for binder to draindown in a particular SMA are presented in Chapter 8. The original Schellenberg’s method and other techniques according to AASHTO and EN 12697-18 standards are also described there.
In most countries, Schellenberg’s or a similar method for determining the quantity of stabilizer in a mix has been applied. The maximum allowable mass of drained-off material is essentially the same almost everywhere and is equal to 0.3%. A recommended, safer limit is 0.2%.
Factors influencing a mixture’s susceptibility to binder draindown are presented in Table 4.1.
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TABLE 4.1 Summary of Factors influencing draindown potential in smA effect on draindown potential
Note: SMA = stone mastic asphalt. |
From the point of view of an SMA mix producer, stabilization efficiency is a decisive factor. But there is one more, equally important point: the quality of a stabilizer must be constant over the whole season of use. What does it matter, exactly, if a product is best at the moment of testing? If the quality varies, we may find ourselves wondering, “What happened? This cellulose is not as good as it used to be.” This variable quality often results in fat spots on the compacted SMA surface.
