What is the Bitumen Extraction Test?
The Bitumen Extraction Test is a laboratory test used to determine the percentage of bitumen (binder) present in a bituminous mixture by extracting the binder with a suitable solvent using a centrifugal extractor. The recovered aggregates are subsequently subjected to sieve analysis to verify compliance with the approved Job Mix Formula (JMF), MoRTH Specifications, and project quality requirements.
3. Test Procedure
The Bitumen Extraction Test shall be carried out in accordance with
ASTM D2172. The test should be performed in a well-ventilated laboratory using appropriate
Personal Protective Equipment (PPE), as extraction solvents are volatile and hazardous.
The following procedure is recommended for determining the binder content of a bituminous mix using a centrifugal extractor.
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Collect a representative sample of the hot bituminous mix from the Hot Mix Plant (HMP), paver hopper, or by extracting a pavement core. Allow the sample to cool to ambient temperature. Break the sample gently into smaller pieces without damaging the aggregates. Quarter the sample, if required, to obtain a representative test portion. Weigh approximately 1000–1500 g to the nearest 0.1 g and record the initial mass as W1.
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Transfer the weighed sample into the centrifugal extractor bowl and spread it uniformly to ensure balanced rotation during extraction.
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Add sufficient quantity of approved extraction solvent (Trichloroethylene (TCE) or equivalent) until the sample is fully submerged. Allow the sample to soak for 30–60 minutes to soften and dissolve the bituminous binder.
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Place a clean, dry, pre-weighed filter paper around the rim of the extraction bowl and securely fasten the cover to prevent the loss of fine aggregates during centrifuging.
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Position a clean collection container below the extractor outlet to collect the bitumen-solvent solution. Ensure proper alignment to prevent spillage.
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Start the centrifugal extractor at a low speed and gradually increase it to approximately 3600 rpm. Continue extraction until the solvent flow becomes negligible.
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Stop the machine completely and add approximately 200–250 ml of fresh solvent. Repeat the extraction until the discharged solvent becomes light straw coloured or nearly colourless, indicating complete removal of the bitumen. Normally, 3–5 extraction cycles are required.
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Remove the filter paper containing the recovered mineral filler and fine particles. Dry it in air followed by an oven maintained at 110 ± 5°C until constant mass is achieved. Record the mass as W3.
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Transfer the extracted aggregates to a tray and dry them in an oven at 110 ± 5°C until constant mass is obtained. Cool the aggregates in a desiccator and record the final dry mass as W2.
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If additional mineral filler remains suspended in the solvent, recover it using a laboratory centrifuge or other approved method. Dry it to constant mass and include it in W3, where applicable.
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Calculate the Bitumen Content (%) using the prescribed formula. Compare the result with the approved Job Mix Formula (JMF) and project specifications. The recovered aggregates may subsequently be used for sieve analysis to verify the aggregate gradation.
Quality Control Checks- Ensure the test sample is representative of the bituminous mix collected from the Hot Mix Plant (HMP), paver hopper, or pavement core.
- Verify that the weighing balance, centrifugal extractor, and drying oven are calibrated before testing. Record all masses to the nearest 0.1 g.
- Use only approved extraction solvent, clean extraction equipment, and dry filter paper throughout the test.
- Prevent the loss of aggregates or mineral filler during sample preparation, extraction, transfer, drying, and weighing.
- Continue the extraction until the discharged solvent becomes light straw coloured or nearly colourless, indicating complete removal of the bituminous binder.
- Dry the extracted aggregates and recovered mineral filler at 110 ± 5°C until constant mass is achieved before recording the final weights.
- Ensure the recovered aggregates are free from visible traces of bitumen before carrying out sieve analysis for aggregate gradation.
- Compare the measured bitumen content and recovered aggregate gradation with the approved Job Mix Formula (JMF) and applicable project specifications.
- Carry out the test in a well-ventilated laboratory using appropriate Personal Protective Equipment (PPE). Keep extraction solvents away from heat, sparks, and open flames.
4. Calculation of Bitumen Content
After completion of the Bitumen Extraction Test, determine the bitumen content (%) by calculating the difference between the original mass of the bituminous mixture and the total mass of the recovered aggregates and mineral filler using the following equation:
Bitumen Content (%) =
[(W1 − (W2 + W3)) / W1] × 100
Where
| Symbol | Description |
|---|
| W₁ | Original mass of the bituminous mix sample (g) |
| W₂ | Mass of oven-dried extracted aggregates (g) |
| W₃ | Mass of recovered mineral filler/fines (g), when recovered separately |
Worked Example
| Observation | Value |
|---|
| Original Sample Mass (W₁) | 1000.0 g |
| Recovered Aggregate Mass (W₂) | 955.2 g |
| Recovered Mineral Filler (W₃) | 6.8 g |
| Bitumen Content | Recovered Material = 955.2 + 6.8 = 962.0 g
Bitumen = 1000.0 − 962.0 = 38.0 g
Bitumen Content = (38.0 / 1000.0) × 100 = 3.80% |
Interpretation- Compare the measured bitumen content with the approved Job Mix Formula (JMF) and the permissible tolerance specified in the project specifications.
- Lower binder content may indicate inadequate binder dosage, incorrect plant calibration, binder leakage, excessive absorption by aggregates, or improper mixing.
- Higher binder content may indicate over-dosing of binder, faulty plant calibration, or batching errors.
- If the measured value falls outside the specified tolerance, identify the cause, rectify the deficiency, and verify compliance before continuing production.
- The recovered aggregates should subsequently be subjected to sieve analysis to verify compliance with the approved aggregate gradation.
5. Precautions, Quality Control Checks & Safety Measures
The accuracy of the Bitumen Extraction Test depends on proper sampling, complete extraction of the bituminous binder, accurate weighing, and safe handling of extraction solvents. The following precautions shall be observed during testing.
- Collect a representative sample from the Hot Mix Plant (HMP), paver hopper, or pavement core.
- Verify that the centrifugal extractor, weighing balance, and drying oven are calibrated and in good working condition before testing.
- Use only approved extraction solvent (such as Trichloroethylene (TCE) or an equivalent solvent) in accordance with laboratory procedures.
- Ensure the extractor cover and filter paper are properly fitted to prevent leakage of solvent and loss of fine aggregates during centrifuging.
- Increase the extractor speed gradually to approximately 3600 rpm. Sudden acceleration may damage the filter paper or result in material loss.
- Repeat the extraction until the discharged solvent becomes light straw coloured or nearly colourless, indicating complete removal of the bituminous binder.
- Dry the recovered aggregates and mineral filler at 110 ± 5°C until constant mass is achieved before recording the final weights.
- Avoid the loss of aggregates or mineral filler during sample preparation, extraction, transfer, drying, and weighing.
- Allow oven-dried materials to cool in a desiccator before weighing to obtain accurate results.
- Carry out the test in a well-ventilated laboratory or under a suitable fume extraction system.
- Wear appropriate Personal Protective Equipment (PPE), including solvent-resistant gloves, safety goggles, laboratory coat, and safety shoes.
- Keep extraction solvents away from heat sources, sparks, open flames, and smoking materials, as they are highly flammable.
- Dispose of used solvents, contaminated filter papers, and other laboratory waste in accordance with applicable environmental and safety regulations.
- Compare the measured bitumen content and recovered aggregate gradation with the approved Job Mix Formula (JMF) before accepting the asphalt mix.
QA/QC Best Practice
For routine production quality control, the Bitumen Extraction Test should always be followed by sieve analysis of the recovered aggregates. Both the bitumen content and aggregate gradation shall comply with the approved Job Mix Formula (JMF) and applicable project specifications before the asphalt mix is accepted.
7. Download Excel Format
Download our ready-to-use Bitumen Extraction Test Excel format designed for laboratory engineers, highway consultants, contractors, and quality control laboratories. The format includes automatic calculations, observation sheets, binder content calculations, and professional reporting.
📥 Download Bitumen Extraction Test Excel Format8. Frequently Asked Questions (FAQs)
- 1. What is the purpose of the Bitumen Extraction Test?
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The test is used to determine the percentage of bitumen present in a bituminous mixture and to recover aggregates for sieve analysis to verify compliance with the approved Job Mix Formula (JMF).
- 2. Which standards cover the Bitumen Extraction Test?
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The test is generally performed in accordance with IS 13826 (Part 1), ASTM D2172, and relevant MoRTH Specifications.
- 3. Which solvent is commonly used?
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Trichloroethylene (TCE) is the most commonly used solvent. Other approved solvents may also be used depending on laboratory procedures and applicable standards.
- 4. Why is aggregate recovered after extraction?
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Recovered aggregates are subjected to sieve analysis to verify whether the aggregate grading complies with the approved Job Mix Formula.
- 5. Why is complete extraction important?
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Incomplete extraction leaves residual bitumen on the aggregates, resulting in an underestimation of the actual binder content.
- 6. How many extraction cycles are normally required?
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Normally three to five extraction cycles are required, depending on the type of asphalt mix and binder content. Extraction should continue until the discharged solvent becomes almost colourless.
- 7. What is the formula for calculating bitumen content?
- Bitumen Content (%) = [(W₁ − (W₂ + W₃)) ÷ W₁] × 100
- 8. What factors can affect the accuracy of the test?
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Improper sampling, incomplete extraction, inaccurate weighing, loss of fine aggregates, damaged filter paper, and incorrect drying procedures can all affect test accuracy.
- 9. Is the Bitumen Extraction Test mandatory in highway projects?
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Yes. It is one of the most important quality control tests for Hot Mix Asphalt and is routinely performed during production and pavement construction.
- 10. Can the recovered aggregates be reused for testing?
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Yes. The recovered aggregates are normally used for gradation analysis and comparison with the approved Job Mix Formula (JMF).
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