Analysis of relaxation time spectra of asphalt mixtures

The relaxation time spectra of three asphalt mixtures, SMA13 with modified binder, Superpave20 with modified binder, and Superpave25 with neat binder, were determined using complex modulus test at various temperatures and loading frequencies. A combination of multiple lognormal distributions was used to represent the relaxation time spectrum function and the parameters were determined using genetic algorithm. The results show that the storage modulus of asphalt mixture increases with increasing loading frequency and decreasing temperature. At intermediate and high temperatures, the loss modulus of asphalt mixture increases as loading frequency increases, while at low temperature the situation is opposite. Accurate storage modulus and loss modulus can be predicted from relaxation time spectrum when a combination of 2 or more lognormal distributions are used. Viscoelastic parameters of asphalt mixture defined at wide loading time ranges can be determined using relaxation time spectra and time-temperature superposition principle, which provides a simple and effective way for analyzing viscoelastic responses of asphalt mixture and pavement structure.