Annually a large number of costs are spent for construction, repair and maintenance of flexible pavements across the country. Investigation of durability and behavior of bitumen can play a critical role in increasing lifetime and reducing the cost of repair and maintenance of pavements. In this regard, many studies have been conducted related to bitumen rheological behavior, often using dynamic analysis methods by the dynamic shear rheometer test. In connection with the bitumen durability, extensive research is carried out, in which entirely durability is invetigated through parameters such as weight loss, penetration grade and softening point (penetration index), and moisture susceptibility in an indirect way. In the present study, rheological behavior and durability of neat bitumen was analyzed by using a different method which enables us to define the parameter of durability as lifetime, so that it can be used in the evaluation and even design of flexible pavements. Many factors affect the durability of bitumen; among these factors, temperature and ultraviolet radiation were selected as the dominant factors affecting aging in this study. Neat 60/70 bitumen produced by Jay Sepahan Oil Refinery was naturally aged in two different thicknesses under the effect of these two factors. Then dumbbell-shaped specimens of unaged and aged bitumen were prepared according toASTM D6723. Limited uniaxial tensile test (creep test) was performed on all samples. Cosequently, viscoelastic constants and creep equations were obtained by analyzing the creep test data and by using the successive residual method for unaged and aged bitumen to discover the effect of aging on creep behavior of neat bitumen. Finally, lifetime relationships of neat bitumen were obtained by the creep test data at two temperatures 25°C and 15°C. These relationships coordinate with the durabiltiy general equation form presented by Zhurkov for viscoelastic materials. This study revealed that creep – time equations of neat bitumen follow the Bürgers model. For neat 60/70 bitumen, instantaneous elastic modulus increased both by the decrease in temperature and by the increase in aging, but applied stress approximately has no effect on the instantaneous elastic modulus which verifies the linear behavior of neat bitumen. Furthermore, relaxation time decreased both by the decrease in the temperature and by the increase in aging, and applied stress causes the relaxation time to augment. Key Words: Creep behavior, durability of bitumen, lifetime, limited uniaxial tensile test, successive residual method, elastic modulus, instantaneous relaxation time
