The amount of aggregate in asphalt concrete mixtures is generally 90 to 95 percent by weight and 75 to 85 percent by volume. Aggregates are primarily responsible for the load supporting capacity of pavement. A few important characteristics of asphalt aggregate, along with a brief discussion of the characteristics, is presented below:
Size and Grading
The maximum size of an aggregate designates the smallest sieve size through which 100 percent of the material will pass. Grading of an aggregate is determined by sieve analysis. Maximum size and grading are controlled by specifications that prescribe the distribution of particle sizes to be used for a particular aggregate material for asphalt mixtures. The distribution of the particle sizes determines the stability and density of the asphalt mixture.
Some aggregates contain foreign or deleterious substances that make them undesirable for asphalt concrete mixtures. (Example: clay lumps, shale, organic material, etc.) The sand-equivalent test, is a method of determining the relative proportion of detrimental fine dust or clay-like materials in the portion of aggregate passing the No. 4 (4.75 mm) sieve.
Aggregates are subjected to additional crushing and abrasive wear during manufacture, placing, and compaction of asphalt concrete mixtures. Aggregates are also subjected to abrasion under traffic loads. They must exhibit an ability to resist crushing, degradation, and disintegration. The Los Angeles Abrasion test measures wear abrasion resistance of aggregates.
Aggregates for asphalt concrete paving should be durable. They should not deteriorate or disintegrate under the action of weather. Items for consideration under weathering action are freezing, thawing, variations in moisture content, and temperature changes. The soundness test is an indication of the resistance to weathering of fine and coarse aggregates.
Asphalt aggregates in Southern California are typically crushed aggregate, having a specified number of fractured faces. All of our asphalt aggregates are tested on a regular basis on-site, with independent testing performed as required. Please contact us if you need any specific test data, or if we can answer any questions relating to asphalt aggregates.