Aggregates, or stone, used in asphalt mixtures (hot mix asphalt, cold mix asphalt, surface treatments) comprise approximately 95 percent of the mixture by mass and roughly 80 percent by volume, the aggregate material(s) used in asphalt concrete have a giant influence on the properties and performance of the mixture. This is a listing of the more important properties for aggregates that are used in asphalt paving mixes:

  • Gradation – the size distribution of the aggregate particles should be a combination of sizes that results in the optimum balance of voids (density) and pavement strength.
  • Particle Shape – aggregate particles should be angular or cubical in shape to minimize surface area. Flat or elongated particles should be avoided.
  • Particle Texture – particles should have a rough rather than smooth texture to minimize the stripping of asphalt cement.
  • Particle Strength – particles should be of sufficient strength to resist degradation or breakdown under compaction or traffic.
  • Durability – particles must be durable enough to remain intact under variable climatic conditions and/or chemical exposure.
  • Specific Gravity – the specific gravity of an aggregate is needed in order to properly design and proportion an asphalt mix.
  • Absorption – the absorption of an aggregate refers to the amount of void spaces within a particle that may be filled with asphalt binder (or air or water), and is a measure of the tendency of an aggregate to absorb asphalt. The higher the absorption, the more asphalt cement will be needed.
  • Unit Weight – the unit weight of an aggregate is an indicator of the compacted density of an asphalt paving mix containing this aggregate and the pavement yield (the volume of pavement that will be required for a given pavement mass).
  • Volume Stability – certain aggregates may undergo volumetric expansion following prolonged exposure to moisture, deicing salts, etc., which may contribute to popouts, ravelling, and random cracking in asphalt pavements.
  • Deleterious Components – some aggregates may contain harmful amounts of potentially reactive components (shale, chert, sulfates, alkalis, expansive silicates, etc.), which may contribute to popouts, ravelling, and cracking in pavements.
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