Sensitivity of Superpave mixtures for development of performance-related specifications

A study was conducted to evaluate the sensitivity of asphalt and dust contents to laboratory predicted top down cracking performance. An attempt was also made to determine whether the present composite pay factor reflects the actual loss in performance. To meet this objective, six mixtures were selected from actual field mixtures that have been placed on interstates and state highways in the State of Florida. All of these mixtures were designed according to the Superpave mix design criteria. Eighteen additional mixtures were reproduced by varying the dust content and/or the asphalt content from the job mix formula (JMF). A thorough analysis was also conducted to ensure that the changes made on the control mixtures were consistent with field observations in variability from actual construction projects.;All of the mixtures were subjected to long-term oven aging according to AASHTO procedures. To evaluate cracking performance, Superpave IDT including resilient modulus tests, creep tests, and strength tests at 10°C were performed. The sensitivity of the accepted variances on properties such as Creep Rate, Fracture Energy, Failure Strain, Dissipated Creep Energy, and Energy Ratio were evaluated.;Based on the analysis conducted, it was found that the current pay factor did not reflect the actual expected loss in performance. Variation in dust content and/or asphalt content that were perfectly accepted under the current practice produced significant loss or unacceptable cracking performance. A conceptual framework for an improved specification was developed that encourages state agencies, contractors, and mix designers to include additional testing at the design level to create quality mixtures that would not be negatively affected by the acceptable variability.