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Aggregate Testing



Aggregate properties of concern in Superpave mix design are generally physical in nature and can be divided up into three major categories:

  • Gradation and size. Particle size distribution.
  • Consensus requirements. Properties associated with physical shape and contamination measurements that can at least partially be controlled during production.
  • Source properties. Properties inherent in the rock source for the aggregate

 

 

 

Gradation & Size

 

The gradation and size test is used to determine aggregate particle size distribution. Size distribution is perhaps the most important aggregate quality associated with the control of HMA mixtures. Aggregate gradation and size affect HMA volumetric properties as well as mixture permeability and workability.
The standard gradation and sieve analysis test is:

  • AASHTO T 27 and ASTM C 136: Sieve Analysis of Fine and Coarse Aggregates

 

Coarse Aggregate Angularity

 

The coarse aggregate angularity test is a method of determining the angularity of coarse aggregate  Coarse aggregate angularity is important to ensure adequate aggregate interlock and prevent excessive HMA deformation under load (rutting).
The standard coarse aggregate angularity tests are:

  • AASHTO TP 61: Determining the Percentage of Fracture in Coarse Aggregate
  • ASTM D 5821: Determining the Percentage of Fractured Particles in Coarse Aggregate
 


 

Flat & Elongated Particles


The flat and elongated particle test is used to determine the dimensional ratios for aggregate particles of specific sieve sizes. This characterization is used in the Superpave specification to identify aggregate that may have a tendency to impede compaction or have difficulty meeting VMA specifications due to aggregate degradation
The standard flat and elongated particles in coarse aggregate test is:

  • ASTM D 4791: Flat Particles, Elongated Particles, or Flat and Elongated Particles in Coarse Aggregates

 

Los Angeles Abrasion

The Los Angeles (L.A.) abrasion test is a common test method used to indicate aggregate toughness and abrasion characteristics. Aggregate abrasion characteristics are important because the constituent aggregate in HMA must resist crushing, degradation and disintegration in order to produce a high quality HMA. The standard L.A. abrasion test subjects a coarse aggregate sample to abrasion, impact, and grinding in a rotating steel drum containing a specified number of steel spheres.
The standard Los Angeles abrasion test is:

  • AASHTO T 96 or ASTM C 131: Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine
 



 

 

 

Fine Aggregate Specific Gravity


The fine aggregate specific gravity test is used to calculate the specific gravity of a fine aggregate sample by determining the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water. It is similar in nature to the coarse aggregate specific gravity test.
The standard fine aggregate specific gravity and absorption test is:

  • AASHTO T 84 and ASTM C 128: Specific Gravity and Absorption of Fine Aggregate

 

 

Coarse Aggregate Specific Gravity


 

The coarse aggregate specific gravity test is used to calculate the specific gravity of a coarse aggregate sample by determining the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water. It is similar in nature to the fine aggregate specific gravity test.
The standard coarse aggregate specific gravity and absorption test is:

  • AASHTO T 85 and ASTM C 127: Specific Gravity and Absorption of Coarse Aggregate