Rutting Resistance of Asphalt Concrete Mixtures that Contain Recycled Asphalt Pavement

This study evaluated the rutting resistance of plant-produced asphalt concrete (AC) mixtures in the laboratory. Nineteen plant-produced AC mixtures were used; these mixtures contained reclaimed asphalt pavement (RAP) amounts that ranged from 0% to 25%. Tests on the mixtures included the dynamic modulus (|E*|) test at multiple temperatures and the flow number (FN) test at 54°C to characterize stiffness and rutting resistance, respectively. Mixtures that contained no RAP showed |E*| values comparable to those that contained 25% RAP in most cases. For most of the 19 mixtures tested, mixtures with lower FNs either contained no RAP, contained 25% RAP, or had PG 64-22 as the design binder grade. Mixtures that contained moderate amounts of RAP (10% and 15%), regardless of design binder grade, had higher FNs than mixtures with either high or low RAP amounts. Statistical analysis showed that the RAP amount was the most significant factor to affect rutting resistance in the mixtures studied. A linear inverse relationship between RAP and FN appeared to describe the data well. As the RAP amount increased, a downward trend occurred in both effective binder content (Pbe) and rutting parameter (G*/sin δ). The effect of RAP on FN was unexpected, because it showed the rutting resistance to decrease with increased RAP. Possible reasons might have been the use of softer asphalt binder in mixtures with higher RAP and the observed decrease in both Pbe and G*/sin δ with increased RAP amounts. More rutting-related mechanistic studies are needed of AC mixtures that contain RAP.