---
title: "Bulk and maximum specific gravity of mix"
subject: "Transportation Engineering I"
chapter: 6
key: "semester_6/transportation_engineering_i:bulk-max-specific-gravity"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/bulk-max-specific-gravity
site: BCT Engineering
---

# Bulk and maximum specific gravity of mix

Transportation Engineering I · Chapter 6: Highway Materials

- Asked in: 2081 Ashwin, 2 marks
- Video: [Max. Theoretical Specific Gravity of Bituminous Paving Mixture |ASTM D2041 |All About Civil Engineer](https://www.youtube.com/watch?v=A5XK4_y1tFk) — All About Civil Engineer
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/bulk-max-specific-gravity
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-6

## Question

What are the bulk specific gravity and maximum specific gravity of bituminous mix?

## Short answer

Bulk specific gravity (Gmb) of compacted mix is weight in air divided by (SSD weight − weight in water). Maximum specific gravity (Gmm) is for voidless mix, measured by Rice test or calculated from component specific gravities. Air voids = (Gmm − Gmb)/Gmm × 100%.

## Answer

#### 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Bulk specific gravity Gmb is found as
   A. Wa/Ww
   B. Wssd/Wa
   C. (Wa - Ww)/Wssd
   D. Wa/(Wssd - Ww) on the compacted specimen including air voids
   Answer: D. It includes voids. (Key point: Bulk)

2. Gmm is the specific gravity of
   A. The loose mix with no air voids (Rice test)
   B. The compacted specimen with voids
   C. Water
   D. The aggregate only
   Answer: A. Measured by vacuum pycnometer. (Key point: Maximum)

3. Air voids Vv =
   A. (Gmb - Gmm)/Gmb x 100
   B. (Gmm - Gmb)/Gmm x 100
   C. Gmm x Gmb
   D. Gmb/Gmm
   Answer: B. Gmb is always less than Gmm. (Key point: Voids)

## Related in Transportation Engineering I

- [Percentage air void in bituminous mix](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3An-80c-air-void) — Transportation Engineering I, chapter 6
- [Marshall method of bituminous mix design](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Amarshall-mix-design) — Transportation Engineering I, chapter 6, asked 9×

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