# ASPHALT MIX DESIGN Combined Bulk Specific Gravity (Gsb) and Absorption of Aggregate Blend

### Combined Bulk Specific Gravity (Gsb) and Absorption of Aggregate Blend

Reference Asphalt Institute MS 2

Bulk Specific Gravity (Gsb) of aggregates is the ratio of the oven-dry mass of a unit volume of aggregate (including both the impermeable and water-permeable void volumes) to the mass of the same volume of water; determined as per AASHTO T 84 and T 85 or ASTM C 127 and C 128.

Detailed descriptions of the tests and calculation tools can be accessed through the following links;

## Absorption

The increase in the mass of aggregate due to water in the pores of the material, but not including water adhering to the outside surface of the particles, expressed as a percentage of the dry mass. The aggregate is considered “dry” when it has been maintained at a temperature of 110 ± 5°C for sufficient time to remove all uncombined water by reaching a constant mass.

## Specific Gravity

The ratio of the mass (or weight in air) of a unit volume of a material to the mass of the same volume of gas-free distilled water at stated temperatures. Values are dimensionless.

## Apparent Specific Gravity

The ratio of the weight in air of a unit volume of the impermeable portion of aggregate at a stated temperature to the weight in air of an equal volume of gas-free distilled water at a stated temperature.

## Bulk Specific Gravity

The ratio of the weight in air of a unit volume of aggregate (including the permeable and impermeable voids in the particles, but not including the voids between particles) at a stated temperature to the weight in air of an equal volume of gas-free distilled water at a stated temperature.

## Bulk Specific Gravity (SSD)

The ratio of the mass in air of a unit volume of aggregate, including the mass of water within the voids filled to the extent achieved by submerging in water for 15–19 h (but not including the voids between particles) at a stated temperature, compared to the weight in air of an equal volume of gas-free distilled water at a stated temperature.

# Calculation:

1. Combined Bulk Specific Gravity for the total aggregate blend is calculated based on the following formula.

$G s b = P 1 + P 2 + ... + P n P 1 G 1 + P 2 G 2 + ... + P n G n$

2. Average Total Absorption for the total aggregate blend is calculated based on the following formula.

$A = P 1 × A 1 + P 2 × A 2 + ... + P n × A n 100$ where:
Gsb = Bulk (Dry) Specific Gravity of the Aggregate
P1, P2 ... Pn = Percentages by weight of aggregates 1,2 .... n.
G1, G2 ... Gn = Bulk (Dry) Specific Gravity of aggregates 1,2 .... n.
A = Average Absorption for the total aggregate blend.
A1, A2 ... An = Absorption of aggregates 1,2 .... n.

Combined (Weighted Harmonic Mean) Specific Gravity and Absorption of Aggregate Blend

Sample Id/Name Specific Gravity (G) Absorption (A) Mass Percentage (P)

Average Specific Gravity and Absorption

Average Specific Gravity:

Average Absorption:

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