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Testing
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Aggregate Tests

An introduction to key tests used to determine the material characteristics and properties of aggregate materials for use in pavement construction. Test results are an important part of mix design and can help predict pavement quality.

Figure 1: Stacked sieves used for a gradation and size test.

Gradation Test

Overview The gradation and size test (Figure 1) is used to determine aggregate particle size distribution. Size distribution is perhaps the single 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. In a gradation and size analysis, a … Read more »

Figure 1: Pouring the aggregate sample into the sieve stack.

Sieve

A sieve is a mechanical device used to separate samples of different sizes. Sieve sizes typically used for Superpave mix design are 1½ in, 1.0 in, ¾ in, ½ in, 3/8 in, No. 4, No. 8, No. 16, No. 30, No. 50, No. 100 and No. 200 (37.5, 25.0, 19.0, 12.5, 9.5, 4.75, 2.36, 1.18, … Read more »

Figure 7: Soaking the sample.

Coarse Aggregate Specific Gravity

Overview The coarse aggregate specific gravity test (Figure 1) 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. … Read more »

Figure 2: Examples of angular and non-angular aggregate.

Coarse Aggregate Angularity

Overview The coarse aggregate angularity (CAA) test is a method of determining the angularity of coarse aggregate (Figure 1). Coarse aggregate angularity is important to ensure adequate aggregate interlock and prevent excessive HMA deformation under load (rutting). The CAA test estimates coarse aggregate angularity by visually inspecting a small sample of coarse aggregate and separating … Read more »

Sand Equivalent_FI

Sand Equivalent

Overview The sand equivalent test (Figure 1) is a rapid field test to show the relative proportions of fine dust or clay-like materials in fine aggregate (or granular soils). The term “sand equivalent” expresses the concept that most fine aggregates are mixtures of desirable coarse particles (e.g., sand) and generally undesirable clay or plastic fines … Read more »

Figure 1: Flat particles (left) and elongated particles (right).

Flat and Elongated Particles

Overview 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. Flat or elongated particles (Figure … Read more »

Figure 1: L.A. abrasion testing equipment.

Los Angeles Abrasion

Overview The Los Angeles (L.A.) abrasion test (Figure 1) 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 … Read more »

Figure 2: More angular (left) vs. more rounded (right) fine aggregate.

Fine Aggregate Angularity

Overview The fine aggregate angularity (FAA) test (Figure 1) is an indirect method of assessing the angularity of fine aggregate. Fine aggregate angularity is important because an excess of rounded fine aggregate (often in the form of natural sand) can lead to HMA rutting. The FAA test estimates fine aggregate angularity by measuring the loose … Read more »

Figure 1: Fine aggregate specific gravity sample and pychnometer.

Fine Aggregate Specific Gravity

Overview The fine aggregate specific gravity test (Figure 1) 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. … Read more »

Figure 1: Triaxial specimen setup.

Triaxial Test

In a triaxial resilient modulus test a repeated axial cyclic stress of fixed magnitude, load duration and cyclic duration is applied to a cylindrical test specimen. While the specimen is subjected to this dynamic cyclic stress, it is also subjected to a static confining stress provided by a triaxial pressure chamber. The total resilient (recoverable) … Read more »

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