1- Department of civil and environmental engineering, Amirkabir university of technology (Tehran Polytechnic), Tehran, Iran
2- Department of civil and environmental engineering, Amirkabir university of technology (Tehran Polytechnic), Tehran, Iran , phajikarimi@aut.ac.ir
Abstract: (1106 Views)
Asphalt mixtures and bitumens are faced with different traffic loading and thermal stresses during their lifetime. Due to their viscoelastic behavior, these materials exhibit different mechanical properties at different temperatures and traffic loading. Viscoelastic properties of bitumens are commonly expressed using the master curves of complex shear modulus (G*) and phase angle (δ) generally created by the horizontal shifting of the frequency sweep test results using shift factors. There are several methods for evaluating temperature shift factors, such as Williams, Landel, and Ferry (WLF) equation, modified Kaelble method, Log-Linear approach, and LCPC method. The LCPC method, developed using the Kramers-Kronig relationship, can be used to accurately evaluate the shift factor of bitumens, mastics, and asphalt mixtures. This study investigated the possibility of generating the master curves of bitumen based on temperature sweep test results rather than frequency sweep test results. Two types of bitumens were investigated in this study, neat bitumen with an 85-100 penetration grade (PG 58-22 performance grade) and SEPS modified asphalt binder with SEPS polymer content of 2, 4, and 6% by weight of the total binder. Temperature sweep tests were performed on all types of bitumens in a range of temperatures between 30 and 90 °C and the frequency of 1.59 Hz. Also, frequency sweep tests were performed on all kinds of bitumens in a range of temperature between 10 and 60 °C and a range of frequency between 0.1 and 100 Hz. The LCPC method was also investigated to calculate the shift factors for the master curves of complex shear modulus and phase angle, and the master curves of viscoelastic properties for all bitumen types are made based on temperature sweep and frequency sweep test results. The results indicated that the SEPS polymer could effectively increase the complex shear modulus and reduce the magnitude of phase angle. So, this polymer improved the rutting resistance of SEPS polymer-modified binders and led to better high-temperature performance of binders. In addition, the LCPC method effectively produced a valid and accurate form of the master curve using temperature sweep test results similar to the master curve using frequency sweep test results. Furthermore, the master curves of complex shear modulus (G*) and phase angle (δ) derived from temperature and frequency sweep test results exhibited comparable patterns and values. By plotting the value of complex shear modulus and phase angle obtained from the temperature sweep master curves versus the complex shear modulus and phase angle obtained from the frequency sweep master curves at the same reduced frequency, it was observed that all points were scattered in the vicinity of the y=x line. It was indicated that the master curves created based on temperature sweep test results have an acceptable approximation and accuracy with the master curves created based on frequency sweep test results. As a consequence, it may be preferable to generate the master curve of viscoelastic characteristics of bitumens using the results of the temperature sweep test, which is faster and more accurate in some conditions, compared to the results of the frequency sweep test.
Article Type:
Original Research |
Subject:
Roads and Transportation Received: 2022/06/24 | Accepted: 2022/12/14 | Published: 2023/05/31