Evaluation of permanent deformation of unmodified and SBS modified asphalt mixtures using dynamic creep test

Recent researches show that there is a serious need for more accurate methods to evaluate polymer modified asphalt mixtures. In this research, dynamic creep test was conducted on unmodified and SBS modified samples, using UTM25 machine to this end. During this work it was attempted to compare the permanent deformation potential of the coarse graded mixtures with dense graded mixtures. Having determined the type of gradation with lower permanent deformation, the amount of polymer to improve the mechanical behavior of the samples made with this type of gradation was investigated. Finally the creep behavior of the samples was estimated by the Zhou three-stage creep model. Based on the obtained results, dense graded mixtures had higher permanent deformation susceptibility than coarse graded mixtures. Moreover, 5% of SBS polymer had better effect on improvement of permanent deformation resistance than 4% and 6%. The mathematical models of creep curves showed that lower stress levels in dynamic creep test can not show the real behavior of asphalt mixtures and particularly the modified mixtures.