Evaluation of cracking performance for polymer-modified asphalt mixtures with high RAP content

Fourteen reclaimed asphalt pavement (RAP) mixtures designed with different combinations of RAP sources, contents (up to 40%) and mixture conditioning levels were evaluated to determine the maximum allowable amount of RAP material in surface courses without jeopardising pavement cracking performance. Extracted RAP binder was blended with virgin polymer-modified asphalt (PMA) binder at various RAP binder replacement ratios. All blends behaved effectively as PMA binder as they met the multiple stress creep recovery (MSCR) % recovery requirement, and in addition they had satisfactory binder fracture energy density values. RAP gradation was found to significantly affect the fracture properties of RAP mixtures as it controls the distribution of RAP binder and potentially the degree of blending between virgin and RAP binder. Increased RAP content resulted in stronger (i.e. higher tensile strength) but more brittle (i.e. lower failure strain and lower mixture fracture energy) mixtures. However, after long-term oven ageing (LTOA) plus cyclic pore pressure conditioning (CPPC) which was used to simulate long-term field ageing conditioning, all RAP mixtures still exhibited dissipated creep strain energy to failure (DCSEf) values above 0.75 kJ/m(3) and energy ratio (ER) values well above 1.0, indicating acceptable cracking performance. It must be emphasised that all RAP mixtures had good gradation characteristics as they all met Superpave design criteria and dominant aggregate size range and the interstitial component (DASR-IC) requirements. Therefore, satisfactory inclusion of up to 40% RAP was acceptable for well-designed PMA mixtures.