Sensitivity of Phase Angle to Testing Conditions of Asphalt Concrete

Abstract

The phase angle has been well established to be used as performance indicators for asphalt cement binder. It is the principal measure of visco-elastic behavior and represents the ratio of viscous over elastic behavior. In the present work, asphalt concrete beam specimens were tested for repeated flexural bending under variable microstrain level of (250, 400, and 750), and three testing environments (5, 20, and 30) °C. Specimens were prepared at optimum binder requirement and at 0.5 % binder above and below the optimum value. The sensitivity of the phase angle was evaluated among the above testing variables. It was observed that the phase angle decline from (66 to 56 and 48) ° under microstrain levels of (250, 400, and 750) respectively. The fatigue life increases from (100 to 3000 and 9000) as the testing environment changes from (5 to 20, and 30) ° C respectively at a phase angle of 10°. At low testing temperature of 5° C, lower phase angle and higher flexural stiffness exists. Finally, at a flexural stiffness of 200 MPa, the phase angle declines from (70 to 55 and 45)° as the asphalt binder content increases from (4.4 to 4.9, and 5.4) % respectively. At a fatigue life of 100, the phase angle rises from (10, to 28, and 36) º when the testing temperature rises from (5 to 20, and 30) ° C respectively. It can be concluded that a significant sensitivity of phase angle is detected for variation in binder content, microstrain level, and testing environment.