The binder extraction test determines the bitumen content of an asphalt mixture — the core QC check that plant-produced mix matches the job mix formula (JMF), with the recovered aggregate then available for gradation testing.
What the Test Measures
A weighed sample of loose or broken-down mix is washed with solvent in a centrifuge extractor until the binder dissolves and drains. Binder content is the mass loss corrected for fines carried into the extract, expressed as a percentage of mix or aggregate mass.
Apparatus Required
- Centrifuge extractor (typically 1500 g or 3000 g bowl) with filter rings
- Approved solvent (trichloroethylene or n-propyl bromide alternatives; follow local HSE rules)
- Balance (0.1 g), oven, and ashing furnace or centrifuge for fines correction of the extract
- Sample splitter and heating tray to break down the mix
Test Procedure
- Warm the mix just enough to separate; weigh about 1–1.5 kg into the extractor bowl.
- Cover with solvent, soak up to 1 h, fit the filter ring and lid.
- Spin at increasing speed, draining the extract; add fresh solvent and repeat until the effluent runs light straw colour (usually 3–6 washes).
- Dry and weigh the extracted aggregate and filter ring; determine fines in the total extract and add back.
Calculation & Reporting
Binder content % = (initial mass − aggregate mass − extract fines) / initial mass × 100. Report with moisture correction if the mix was sampled hot from the plant, and attach the recovered-aggregate grading.
Acceptance Criteria
Plant mix normally must sit within ±0.3% of the JMF binder content; recovered grading within JMF tolerances per sieve (commonly ±4–5% mid sieves, ±2% on 75 µm). Repeated low binder results indicate plant metering drift — flag immediately.
Frequently Asked Questions
Ignition oven or solvent extraction?
The ignition method (ASTM D6307) avoids solvents and is faster, but needs a mix-specific correction factor and alters some aggregates. Solvent extraction remains the referee method and preserves aggregate for grading.
How is the fines correction determined?
Either ash a measured aliquot of the extract or centrifuge the full extract and weigh the recovered mineral matter. Skipping this correction understates aggregate mass and overstates binder content.
Recommended Apparatus
NL Scientific manufactures the ECO-SMARTZ Centrifuge Extractor Apparatus for this method. Browse the full Bitumen & Asphalt Testing Equipment range or request a quotation from our engineers.
