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Gradation & SIze
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The gradation and size test (Figure 1) is used to determine aggregate particle size distribution. Size distribution is perhaps the single most important aggerate quality associated with the control of HMA mixtures. Aggregate gradation and size affect HMA volumetric properties as well as mixture permeability and workability.
In a gradation and size analysis, a sample of dry aggregate of known weight is separated through a series of sieves with progressively smaller openings. Once separated, the weight of particles retained on each sieve is measured (Figure 2) and compared to the total sample weight. Particle size distribution is then expressed as a percent retained by weight on each sieve size. Results are usually expressed in tabular or graphical format. Graphical displays almost always use the standard 0.45 power gradation graph.
The standard gradation and sieve analysis test is:
