Tracking Degree of Blending Between Recycled and Virgin Binder Through Asphalt Mix Phase Angle

Performance of Reclaimed Asphalt Pavement (RAP) in a new mix depends on the degree of blending between the aged asphalt binder of the RAP and the new virgin binder. The extent of blending determines the homogeneity of the new mix and thus its performance. A recent study by ExxonMobil and University of Waterloo has indicated that silo storage improves homogeneity of RAP-containing mixes post manufacturing. Samples were collected at selected silo storage durations. Resistance to rutting, fatigue and low temperature cracking exhibited improvement. However, the complex modulus mastercurves exhibited a reduction in |E*| values at lower frequencies up to 12 h of storage, which was unexpected. In addition to lower |E*| values, the slopes of mastercurves were changing with silo storage time. Literature suggests that the slope of a log-log plot of |E*| versus frequency is an estimate of the phase angle of the material. Therefore, deriving phase angle from the mix mastercurves, the evolution of blending between RAP and virgin binder could also be tracked. Data suggests that the derived phase angle is also sensitive enough to detect the aging that would happen as a result of a prolonged silo storage or incompatible binder chemistry.