Reviewed by Er. Inderjit Sharma (Retd.), Punjab PWD
What is specific gravity of bitumen? It tells you how heavy bitumen is compared with the same volume of water at 27 °C. Paving bitumen is usually just a little heavier than water, around 1.01–1.05.
Why it matters: it’s needed to work out the volumes in bituminous mix design (air voids, VMA, VFB), to convert bitumen litres into kilograms, and as a quick check for contamination.
This guide follows IS 1202.
The Specific Gravity Bottle
The Four Weighings
Apparatus Required
Specific gravity bottle
50 ml, with capillary stopper; wide-mouth type for thick binders.
Water bath (27 ± 0.1 °C)
Deeper than the bottle; keeps an exact temperature.
Balance (0.01 g)
Weighs the bottle at each stage.
Hot plate & funnel
Warm bitumen gently; pour without touching the neck.
Boiled distilled water
Boiled and cooled to remove dissolved air.
Procedure
- Clean, dry and weigh the empty bottle with its stopper: A.
- Fill it with freshly boiled and cooled distilled water, insert the stopper, and keep it in the water bath at 27 ± 0.1 °C for at least 30 minutes. Wipe it dry and weigh: B.
- Empty and dry the bottle. Heat the bitumen gently until it flows (don’t overheat; avoid loss by evaporation).
- Warm the bottle and pour bitumen in until it is about half full, using a small funnel. Keep bitumen off the neck and avoid air bubbles.
- Let it stand for about 30 minutes so air escapes, cool it to 27 °C, and weigh with the stopper: C.
- Fill the rest of the bottle with boiled, cooled distilled water, with no air bubbles. Insert the stopper.
- Keep it in the bath at 27 ± 0.1 °C for at least 30 minutes, wipe dry and weigh: D.
- Do two tests and report the mean.
Calculation
What each part means
C − A = weight of bitumen
B − A = weight of water filling the bottle
D − C = weight of water filling the rest
(B − A) − (D − C) = weight of water with the same volume as the bitumen
📝 Worked example
A = 30.00, B = 80.00, C = 55.60, D = 80.20 g
Bitumen = 25.60 g
Equal-volume water = 50.00 − 24.60 = 25.40 g
SG = 25.60 ÷ 25.40 = 1.01
Try It: Specific Gravity Calculator
Enter the four weights (g). The values filled in are the worked example.
Bonus: litres ↔ kilograms of bitumen
Precautions
💧 Boiled distilled water
Use freshly boiled and cooled distilled water so no dissolved air forms bubbles in the bottle.
🌡️ Exactly 27 °C
Keep the bath at 27 ± 0.1 °C and weigh quickly after taking the bottle out; temperature changes the volume.
🫧 No air bubbles
Let the bitumen stand so air escapes, and top up with water slowly. Bubbles give a wrong result.
🔥 Don’t overheat bitumen
Heat only until it flows; overheating hardens it and causes loss of light oils. Wear gloves.
Practical Tips for Site Engineers
1. Typical Values
| Binder | Typical specific gravity at 27 °C |
|---|---|
| Paving bitumen (VG-10, VG-30, VG-40) | 1.00–1.05 |
| Polymer modified bitumen (PMB) | about 1.00–1.04 |
| Bitumen emulsion | about 0.99–1.02 |
Typical ranges only; use the tested value for calculations.
2. Good Site Habits
- Use it in mix design: Marshall or Superpave volumetrics need the specific gravity of the actual binder. Using a guessed value gives wrong air voids and VMA.
- Check tanker deliveries: convert litres to tonnes using the tested specific gravity, and correct for temperature, before accepting quantities.
- Spot contamination: a value much lower than usual may mean the bitumen was mixed with diesel or a lighter oil; a much higher value may point to contamination. Investigate before use.
- Test every source and grade: keep the result with the other bitumen test records (penetration, softening point, viscosity, ductility).
- Sample correctly: take samples from the tanker or drum as per the standard, in clean, labelled tins.
Key Takeaways
- Specific gravity of bitumen is about 1.01–1.05 at 27 °C.
- Weigh the bottle empty (A), full of water (B), half full of bitumen (C), and bitumen + water (D).
- SG = (C − A) ÷ [(B − A) − (D − C)]; keep everything at 27 ± 0.1 °C.
- Use boiled, cooled distilled water; avoid air bubbles and overheating.
- On site: use the tested value in mix design and tanker conversions; unusual values can point to contamination.
References: IS 1202: Methods for Testing Tar and Bituminous Materials – Determination of Specific Gravity; IS 73: Paving Bitumen – Specification; MS-2 / MoRTH Specifications (Section 500) for mix design.