Bulk and maximum specific gravity of mix

Bulk specific gravity ($G_{mb}$)

The bulk specific gravity of a compacted bituminous mix is the ratio of the weight in air of a given volume of the compacted mix (including the air voids) to the weight of an equal volume of water at the same temperature. It is found by weighing the specimen in air ($W_a$), in water ($W_w$) and SSD ($W_{ssd}$):

$$G_{mb} = \frac{W_a}{W_{ssd} - W_w}$$

It is used to find the unit weight and the voids (air voids, VMA, VFB) of the compacted mix.

Maximum (theoretical) specific gravity ($G_{mm}$)

The maximum specific gravity is the specific gravity of the loose mix with no air voids: the ratio of the weight of the voidless mix (aggregate + binder) to the weight of an equal volume of water. It is measured on the loose mix in the vacuum-pycnometer (Rice) test, or calculated:

$$G_{mm} = \frac{100}{\dfrac{W_s}{G_{se}} + \dfrac{W_b}{G_b}}$$

where $W_s$ and $W_b$ are the percentages by weight of aggregate and binder, $G_{se}$ the effective specific gravity of the aggregate, and $G_b$ the specific gravity of the binder.

Use

$$V_v = \frac{G_{mm} - G_{mb}}{G_{mm}}\times 100\%$$

$G_{mb}$ is always less than $G_{mm}$ because of the air voids.