Like OGFC, the stability of SMA is derived from stone-to-stone contact, and asphalt binder films are much thicker than densely graded mixtures.

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Stability in SMA comes primarily from the aggregate skeleton: the stones interlock and carry the load through stone-to-stone contact, while the asphalt binder mainly fills voids and coats the particles. Because SMA uses a high asphalt content to stabilize the mix, the binder forms thicker films around the aggregates than you’d see in a densely graded mixture. This combination gives a strong, load-bearing structure where the skeleton provides most of the stability, with the thicker binder film helping to lock the particles together without relying on lubrication from the binder. Open-graded mixes like OGFC share the idea of relying on aggregate contact for stability, but SMA achieves its stability through the interlock of the stone matrix plus a richer binder coat, which is why the statement is true.