SMA mixtures are chiefly laid as wearing courses. Binders for them should therefore have suitable properties for asphalt mixtures applied to that layer.
The majority of SMAs are placed in moderate climates. Therefore the SMA binder is usually an unmodified binder, or sometimes a polymer-modified one, with a penetration between 50 and 100 (0.1 mm) at 25°C. In several countries, multigrade
Requirements for SMA Aggregates (Coarse, Fine, and Filler) in the United States
properties requirement comments
coarse aggregates
<30 There is a suggestion to use additional test
methods like Micro-Deval or SGC degradation test. Despite experiences with aggregates of LA 30-45%, their use is not recommended due to possible grain crushing during compaction both in the laboratory and on the road.
<20 at 3:1, Aggregates that have a high percentage of
<5 at 5:1 flat and elongated particles:
• Tend to break down during compaction
• Have higher voids within the aggregate
Requirements apply to a whole coarse aggregates fraction in SMA but not to individual materials (fractions).
100% one face, Property is important for interlocking of >90% two faces aggregates skeleton.
<2
<15 in sodium Tests show that there is good correlation
sulfate, <20 in between magnesium sulfate soundness and
magnesium sulfate micro-Deval abrasion test.
Fine aggregates
<15 in sodium See Coarse Aggregates.
sulfate, <20 in magnesium sulfate
>45 Indication of interlocking potential of fine
aggregates
<25 The liquid limit is the water content at
which the material passes from a plastic Nonplastic to a liquid state. The plasticity index is
the numerical difference between the liquid limit and the plastic limit; it is the moisture content at which the material is in a plastic state. The goal is to eliminate aggregates with clay or silt particles.
(Continued)
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TABLE 5.5 (CONTINUED) Requirements for SMA Aggregates (Coarse, Fine, and Filler) in the United
Note: AASHTO = American Association of State Highway and Transportation Officials; ASTM = American Society for Testing Materials; LA = Los Angeles; SGC = Superpave Gyratory Compactor; SMA = stone matrix asphalt. |
binders are also used. Under special circumstances, especially in countries with a cold climate, soft binders (with penetration higher than 100 at 25°C) are used. A steady increase in the percentage of polymer-modified binders in SMA mixtures has been observed recently. Considerable research (see Chapter 12) has proved that a polymer-modified binder substantially improves the characteristics of a finished SMA layer.
