Aggregate Weight-Volume Relationships and Terms

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Basic aggregate weight-volume relationships are important to understand aggregate structure and properties. Fundamentally, aggregate volume properties are desired, but since mass measurements are typically much easier, masses are typically taken then converted to volume by using specific gravities. The following is a brief discussion of the more important mass-volume relationships of aggregates.

**Figure 1.** Aggregate volume schematic (from Roberts et al., 1996).

**Table 1.**
G_(sa)	equals	Apparent specific gravity of the aggregate	W_s	equals	Oven-dry weight of aggregate
G_b	equals	Asphalt binder specific gravity	V_S	equals	volume of the solids
G_(sb)	equals	Bulk specific gravity of the aggregate	V_(pp)	equals	volume of water permeable pores
G_(se)	equals	Effective specific gravity of the aggregate	V_(ap)	equals	volume of pores absorbing asphalt
G_(mb)	equals	Bulk specific gravity of the compacted mixture	P_b	equals	Asphalt content by weight of mix (percent)
G_(mm)	equals	Maximum theoretical specific gravity of the HMA mixture	P_s	equals	Aggregate content by weight of mix (percent)
G₁	equals	Coarse aggregate specific gravity (retained on the 4.75 mm (No. 4) sieve)	P₁	equals	Coarse aggregate fraction (retained on the 4.75 mm (No. 4) sieve)
G2	equals	Fine aggregate specific gravity (between the 4.75 mm (No. 4) and 0.075 mm (No. 200) sieve)	P₂	equals	Fine aggregate fraction (between the 4.75 mm (No. 4) and 0.075 mm (No. 200) sieve)
G₃	equals	Mineral filler specific gravity (passing the 0.075 mm (No. 200) sieve)	P₃	equals	Mineral filler fraction (passing the 0.075 mm (No. 200) sieve)
γW	equals	Unit weight of water	V_(pp) – V_(ap)	equals	volume of water permeable pores not absorbing asphalt

Specific Gravities

Apparent Specific Gravity ( $G_{sa}$ )

Includes only the volume of the aggregate particle. It does not include the void volume that becomes filled with water during the test soak period. Ideally, it would not include any void volume but in reality some voids may not become entirely filled with water during the test soak period. The void volume that does not become filled with water is thus counted with the solid volume. Since it is intended to only measure the specific gravity of the solid volume, it will be the highest of the three aggregate specific gravities.

Standard apparent specific gravity tests are:

AASHTO T 84 and ASTM C 127: Specific Gravity and Absorption of Fine Aggregate
AASHTO T 85 and ASTM C 128: Specific Gravity and Absorption of Coarse Aggregate

Bulk Specific Gravity ( $G_{sb}$ or BSG)

Includes the volume of the aggregate particle plus the void volume that becomes filled with water during the test soak period. Since it includes the void volume, bulk specific gravity will be less than apparent specific gravity. It is very important to measure $G_{sb}$ as accurately as possible. Since it is used to convert weight measurements to volumes, any small errors in $G_{sb}$ will be reflected in significant volume errors, which may go undetected.

Standard bulk specific gravity tests are:

AASHTO T 84 and ASTM C 127: Specific Gravity and Absorption of Fine Aggregate
AASHTO T 85 and ASTM C 128: Specific Gravity and Absorption of Coarse Aggregate

Effective Specific Gravity ( $G_{se}$ )

Typically used with HMA. The ratio of the mass in air of a unit volume of a permeable material (excluding voids permeable to asphalt) at a stated temperature to the mass in air (of equal density) of an equal volume of gas-free distilled water at a stated temperature. $G_{se}$ includes the volume of the aggregate particle plus the void volume that becomes filled with water during the test soak period minus the volume of the voids that absorb asphalt. Effective specific gravity lies between apparent and bulk specific gravity.

The standard effective specific gravity calculation is contained in:

AASHTO PP 19: Standard Practice for Volumetric Analysis of Compacted Hot-Mix Asphalt (HMA)

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Aggregate unit weight and voids

AASHTO T 19

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Pavement Interactive. (2018, September 5). Aggregate weight-volume relationships and terms. HeadLight. Retrieved [the date you read it], from https://pavementinteractive.org/reference-desk/materials/aggregate/aggregate-weight-volume-relationships-and-terms/

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Pavement Interactive. (2018). “Aggregate Weight-Volume Relationships and Terms.” HeadLight, <https://pavementinteractive.org/reference-desk/materials/aggregate/aggregate-weight-volume-relationships-and-terms/> ([the date you read it]).

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@misc{pavint-aggregate-weight-volume-relationships-and-terms,
  author = {{Pavement Interactive}},
  title = {Aggregate Weight-Volume Relationships and Terms},
  year = {2018},
  publisher = {HeadLight},
  howpublished = {\url{https://pavementinteractive.org/reference-desk/materials/aggregate/aggregate-weight-volume-relationships-and-terms/}},
  note = {Accessed [date]}
}

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