Bitumen Extraction Test:
A laboratory method to determine exact bitumen (binder) content in asphalt mixes using solvent extraction (centrifuge / reflux). Also used to recover aggregates for gradation.
| Parameter | Details |
|---|
| Standard | IS 13826 / ASTM D2172 |
| Purpose | Determine bitumen content & recover aggregates for gradation |
| Sample | ~1000 g typical |
1. OBJECTIVE
To determine percentage of binder (bitumen) in a bituminous mix by cold solvent extraction using a centrifugal extractor (ASTM D2172 / IS 13826).
2. APPARATUS
- Centrifugal extraction machine
- Analytical balance (0.1 g)
- Cold solvent (benzene / petrol / trichloroethylene)
- Filter paper (Watt 60)
- Oven, beakers, spatula, glass plate
- PPE: gloves, goggles, extractor ventilation
3. PROCEDURE
- Weigh a representative sample (W1 ≈ 1000 g) and place into the extractor bowl.
- Add sufficient commercial benzene (or specified solvent) to cover the sample and allow to stand up to 1 hour to soften the bitumen.
- Line the bowl with pre-weighed filter paper and assemble the bowl with the paper in place. Place a beaker to collect the solvent/bitumen extract.
- Start the extractor slowly and increase speed gradually up to 3600 rpm. Maintain until solvent flow reduces significantly.
- Stop the machine and add about 200 ml fresh solvent. Repeat extraction cycles at least 3 times or until the extract becomes light straw in colour.
- Remove filter paper with retained fines; dry in air then oven at 115°C to constant weight (record Wf).
- Recover fines in solvent by centrifuging the extract; dry and weigh recovered fines (W3).
- Dry remaining aggregate in oven to constant weight and record as W2.
- Record all weights and proceed to calculation.
4. CALCULATION & EXAMPLE
% Binder Content = [(W1 − (W2 + W3)) / W1] × 100
Where:
- W1 = Original weight of sample (g)
- W2 = Weight of aggregate after extraction (g)
- W3 = Weight of fines recovered from extract (g)
| Parameter | Value (g) |
|---|
| W1 (sample) | 1000.0 |
| W2 (after extraction) | 955.2 |
| W3 (fines) | 6.8 |
| Binder % | 3.80% |
5. MoRTH Binder Content Requirements (Typical)
| Layer | Typical Binder % |
|---|
| DBM (Grade-I) | 3.5 – 4.5% |
| DBM (Grade-II) | 4.0 – 4.5% |
| BC (Grade-I) | 5.0 – 5.4% |
| BC (Grade-II) | 5.2 – 5.6% |
6. NOTES & SAFETY
- Handle solvents in a ventilated area and use PPE.
- Ensure extractor lid seals to avoid solvent loss.
- Dispose used solvent as hazardous waste per local rules.
- Repeat extraction until extract clears; incomplete extraction underestimates binder %.
8. FAQ
Q: Which solvent is used?A: Commercial benzene, trichloroethylene, or petrol—choose as per lab regulations and safety.
Q: How many cycles are needed?A: Typically 3 cycles or until extract becomes light straw in colour.
Q: How to calculate binder %?A: % Binder = [(W1 − (W2 + W3)) / W1] × 100
