Critical assessment of the Multiple Stress Creep Recovery (MSCR) test on bitumen performance: a comparative experimental study

Conventional DSR high-temperature performance grading uses G*/sin delta to characterise small-strain oscillatory binder response but does not directly quantify residual strain after repeated loading. This study presents a same-formulation comparison of DSR grading and multiple stress creep recovery (MSCR) response for 60/70 penetration-grade bitumen modified with 6% linear styrene-butadiene-styrene (SBS) and 1.5% Sasobit. The available laboratory record comprised a DSR temperature sweep assessed using the original-binder criterion G*/sin delta ≥ 1.0 kPa and MSCR testing at 76°C under 0.1 and 3.2kPa. Instrument outputs for percent recovery (%R_3.2), non-recoverable creep compliance (J_nr3.2) and stress sensitivity (J_nr-diff) were extracted and interpreted against AASHTO M 332 thresholds. The DSR continuous pass/fail temperature was 95.6°C. Recovery decreased from 93.61% at 0.1kPa to 59.55% at 3.2kPa, while J_nr3.2 increased from 0.0524 to 0.4852kPa⁻¹. Although J_nr3.2 was below the commonly used 0.5kPa⁻¹ threshold for an E traffic suffix, J_nr-diff was 825.38%, indicating pronounced stress sensitivity. The paper’s contribution is to show, for the same modified binder, that a favourable DSR grade and low J_nr3.2 can coexist with a stress-sensitivity concern that would be missed if either result were interpreted alone. The findings do not establish mixture or field rutting performance. Since only one formulation and no replicate-level data were available, Malaysian specification use requires documented preparation and ageing, replicate testing, justified test temperature, mixture-level validation and field monitoring.