Time-temperature-aging-depth shift functions for dynamic modulus master curves of asphalt mixtures

Oxidative aging is one of the significant environmental effects on asphalt pavement performance. This study aims to characterize the aging viscoelastic property of asphalt mixtures such as dynamic modulus at different aging times and pavement depths, then develops two aging shift functions to account for the effects of long-term aging and non-uniform field aging in the pavement depth. Tensile creep test and direct tension test are conducted on 12 laboratory-mixed-laboratory-compacted (LMLC) asphalt mixtures with three laboratory aging times and 16 field-aged asphalt mixtures with four field aging times, respectively. The dynamic modulus of LMLC mixtures is determined from the tensile creep test and the elastic-viscoelastic correspondence principle is utilized to obtain the dynamic modulus of field-aged asphalt mixtures from the direct tension test. The dynamic modulus master curves of the asphalt mixtures at different aging times and pavement depths are constructed using the modified Christensen-Anderson-Marasteanu (CAM) model. It is shown that both of the rheological index and glassy modulus increase with aging time and the crossover frequency decreases with aging time. The long-term aging shift function is determined as a function of aging time, acceleration factor, activation energy, and aging temperature. The depth shift function is determined as a function of pavement depth. With the aid of the two aging shift functions, it becomes possible to construct a single dynamic modulus master curve after taking into account the effects of temperature, long-term aging, and non-uniform aging with pavement depth below the surface.