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Effect of long-term ageing on RAP mixtures: laboratory evaluation of plant-produced mixtures

As the use of reclaimed asphalt pavement (RAP) in asphalt concrete mixtures increases, it is important to understand how the addition of already aged asphalt binders affects the overall properties and performance of the mixture. In this study, four plant-produced mixtures containing 0%, 20%, 30%, and 40% RAP were long-term oven aged in the laboratory to three levels. Mixture testing included uniaxial complex modulus and fatigue. Recovered binder testing included performance grading (PG) and rheological characterisation. The mixture testing showed that the RAP mixtures stiffen due to laboratory ageing at a slower rate than virgin mixtures and that the impact of the presence of RAP on material properties decreases with ageing time. The relative fatigue performance of the mixtures changes dramatically in stress versus strain control, indicating the importance of linking mixture and pavement design. The recovered binder properties show increase in the high continuous PG, minimal impact at the intermediate continuous PG and a slight increase in the low continuous PG with ageing time. The complex shear modulus shows an increase in stiffness and a decrease in phase angle with ageing. The binder and mixture properties generally show the same qualitative trends with respect to RAP content and ageing level; quantitative comparisons of several parameters show some correlation, indicating that binder properties may be used to evaluate the expected mixture properties measured in the lab.