Examining ΔT _c : Variability Factors and Relationships with Other Rheological Shape Parameters

The Illinois Department of Transportation implemented a minimum ΔT c specification requirement of −5°C after 40 h of pressure aging vessel (PAV) aging for neat asphalt binders in 2023. Unfamiliarity with the ΔT c parameter and unknowns with regard to variability from extended PAV aging created an opportunity for multiple interlaboratory studies to quantify variability and identify any potential bias within the Illinois asphalt binder testing community. Additionally, a small-scale experiment was conducted to directly compare the impact on ΔT c results after multiple extended PAV aging conditions: two 20-h PAV aging cycles and one continuous 40-h PAV cycle. Various rheological shape parameter results after standard 20-h PAV aging were evaluated to determine correlation with ΔT c results after extended PAV aging. Findings show that variability in ΔT c is primarily driven by bending beam rheometer stiffness, but m-value d2s% values more often exceeded allowable ranges in AASHTO T 313. Estimated creep stiffness, S, had higher d2s% magnitude, but more often fell within the allowable range, whereas m-value had a lower d2s% magnitude, but fell out of the allowable range more frequently. The control sample results indicated that PAV aging is a minimal factor in reproducibility. Two 20-h PAV cycles showed slightly more aging than the continuous 40-h PAV aging, but the difference was not statistically significant. It was found that the PG58-28 samples were more sensitive to the two 20-h PAV cycles than the PG64-22 samples. The R-value after 20 h of PAV aging was shown to be the most reliable indicator of ΔT c after extended aging for binders studied.