The Marshall stability test is the classic method for designing and checking asphalt (bituminous) mixtures, measuring the maximum load a compacted specimen carries and its deformation at failure.
What the Test Measures
Stability is the peak load a 101.6 mm Marshall specimen resists at 60°C; flow is the deformation at that peak. Together with density and air-void analysis they define the optimum bitumen content of an asphalt mix.
Apparatus Required
- Marshall stability testing machine with breaking head and loading at 50 mm/min
- Water bath at 60°C
- Marshall compaction hammer and moulds
- Load and flow measurement (proving ring/load cell and flow meter)
NL Scientific manufactures the Digimatic Marshall Stability Compression Tester 50kN and the full bitumen & asphalt testing range, built to ASTM, EN, BS and AASHTO requirements with ISO/IEC 17025 accredited calibration.
Test Procedure
- Compact specimens to the required number of blows and determine bulk density.
- Condition specimens in the 60°C water bath for 30–40 minutes.
- Place the specimen in the breaking head and seat it in the machine.
- Apply load at 50 mm/min until the maximum load is reached.
- Record the peak load (stability) and the corresponding flow.
Calculation & Reporting
Report stability (kN, corrected for specimen thickness) and flow (mm or 0.25 mm units). Plot stability, flow, density and voids against bitumen content to select the optimum binder content.
Acceptance Criteria
Minimum stability and a flow range are set by the specification (for example, minimum stability values for heavy traffic with flow typically 2–4 mm). Refer to the governing asphalt mix-design specification.
Frequently Asked Questions
What does a high flow value indicate?
Excessive flow indicates a mix that is too soft or over-bitumen, prone to rutting. Low flow with low stability suggests a brittle mix.
Is Marshall still used with Superpave available?
Yes. Marshall mix design remains widely specified, especially outside North America, and is valuable for routine QC of asphalt plants.
Need the right equipment for your laboratory? Contact NL Scientific for a quotation — Asia’s leading manufacturer of civil engineering and material testing equipment, shipping worldwide.
