Physical Hardening in Asphalt Mixtures

This paper documents and discusses the physical hardening phenomenon in asphalt mixtures and the implications for pavement performance. Physical hardening can broadly be defined as the gradual stiffening of a material during isothermal storage at low temperatures brought about by changes in structure (wax crystallization, asphaltene aggregation, volume relaxation) rather than chemical composition (volatilization, exudation, oxidation). Seven asphalt mixtures from an eastern Ontario trial on Highway 417 were tested in single-edge-notched tension (SENT) configuration at -22°C after one hour, 24 hours, and 72 hours of conditioning at -10°C. Decreases in the crack mouth opening displacement at peak load (CMODp) were used to quantify the reduction in strain tolerance in the presence of severe constraint (notches). Increases in the crosshead displacement at peak load (CDp) were used to assess global damage (microcracking) during conditioning and subsequent testing. After 72 hours of conditioning at -10°C, the changes in CMODp ranged from -16% to -56%, whereas changes in CDp varied from +23% to +223%. The absolute CMODp correlated well with performance for this trial, with three poor-performing mixtures showing significant and early cracking in service. These results provide evidence that isothermal conditioning can induce microcracking with simultaneous losses in strain tolerance in the presence of severe constraint (notches), which likely contributes to thermal cracking in service.

並列關鍵字

Asphalt cement ； Physical hardening ； Specification grading ； Thermal cracking

國際替代計量

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