STP1041

    The Role of Asphalts in Rational Mix Design and Pavement Performance

    Published: Jan 1989


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    Abstract

    Conceptually, a rational mix design procedure should provide test parameters for input into mechanistic pavement design methods and analytical procedures to predict high and low-temperature pavement performance. It is suggested that high-temperature evaluation be performed to design asphalt concrete mixtures using a gyratory testing machine (GTM) to simulate (1) field compaction at conventional mix temperatures, and (2) traffic densification at 60°C. This would provide a better indication of mixture behavior and sensitivity to changes in aggregate blend and asphalt content than current mix design methods. The major advantage of this approach is that the changes in the shear response of the mix can be evaluated easily over the range from as-compacted to highly densified. Conventional mix design procedures are essentially one-point tests that do not provide information rate of densification or changes in stability when the mix density changes.

    Tentative recommendations are presented for quality control and acceptance testing using gyratory testing of plant-produced hot mix. Advantages of this procedure are its sensitivity to combined changes in gradation and asphalt content, simplicity, and potential for more intensive testing of produced hot mix.

    The low temperature (<25°C) properties and behavior of asphalt concrete paving mixtures are controlled by the Theological properties of the asphalt concrete. Therefore, it is essential that specifications for asphalts or mixtures or both be established to minimize the potential for excessive age hardening and pavement cracking. Research investigations have found cracking to be related to thermal contraction, thermal gradients that produce pavement rippling, vehicular loads, and the viscosity of the asphalt binder during cooling of the pavement. A stress analysis is presented to illustrate the combined effect of asphalt concrete moduli, underlying pavement support, and heavy wheel loading on the maximum pavement stresses developed at designated low temperatures.

    A brief discussion on the selection of asphalts and polymer modification is presented to illustrate the major deficiencies in current test methods and specifications. Most asphalt specifications require only tests at 25°C and higher that neglect behavior at low temperatures. Low-temperature viscosity tests should be incorporated in all asphalt specifications. A comprehensive model asphalt specification is presented that includes viscosity tests at 15 and 25°C. An example is given to demonstrate how the viscosity-temperature relationships enhance our ability to interpret asphalt, polymer modified asphalt, and mix behavior at low temperature.

    Keywords:

    mix design, asphalt specifications, gyratory testing machine, viscosity, low temperatures, stress analysis, pavement performance, thermal contraction, thermal rippling, polymers, asphalt concrete


    Author Information:

    Ruth, BE
    Professors and doctoral candidate, University of Florida, Gainesville, FL

    Tia, M
    Professors and doctoral candidate, University of Florida, Gainesville, FL

    Badu-Tweneboah, K
    Professors and doctoral candidate, University of Florida, Gainesville, FL


    Paper ID: STP20069S

    Committee/Subcommittee: D04.40

    DOI: 10.1520/STP20069S


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