Evaluate the fracture and fatigue resistances of hot mix asphalt containing high percentage reclaimed asphalt pavement (RAP) materials at low and intermediate temperatures

摘要

When applying recycled asphalt technology in a flexible pavement project, most of the concerns are related to low-temperature fracture and fatigue cracking, since the stiffness of hot mix asphalt (HMA) mixtures could dramatically increase through adding a high percentage of reclaimed asphalt pavement (RAP) materials. Therefore, the purpose of this research was to evaluate fracture and fatigue resistance of asphalt mixtures in relationship to various proportions of reclaimed asphalt pavement materials, and two RAP addition methods (Traditional and Fractionated Methods) at different temperatures (-10, -20, and -30°C for fracture resistance assessment, and 20°C for examination to fatigue resistance). Fracture and fatigue experiments, separately, utilized two types of RAP from different resources. Asphalt mixture samples for both facture and fatigue tests were prepared with RAP using the as is gradation (Traditional) and splitting of the RAP into coarse and fine fractions (Fractionated) methods with three RAP binder content replacement percentages (30, 40, and 50%).Based on the findings and experimental observations on the fracture energy test results, which underestimate fracture resistance at certain testing temperatures, this research was extended to critically investigate the suitability for the semi-circular bend (SCB) test protocol to evaluate the fracture resistance of asphalt mixtures. By applying fracture mechanistic theories, some test procedures were modified to ensure measurement is the toughness, which better represents fracture resistance of the material. Fracture toughness tests performed on asphalt mixtures containing 30, 40, and 50% RAP reveal their fracture resistance changes with varying temperatures. None of the asphalt mixtures evaluated in this research preserves its own advantage for the entire temperature range from -30 to -10°C. The toughness of traditionally batched mixtures is generally larger than the fractionated prepared mixtures. However, a statistically significant difference is not detected.Moreover, asphalt mixture beam fatigue and binder fatigue tests (time-sweep test) were performed as well. The RAP materials evaluated in beam fatigue and binder fatigue tests were different from the RAP materials utilized in the fracture experiments. Beam fatigue samples also underwent free-thaw cycling treatments for evaluation. Rather than based solely on S-Nf curves to illustrate the fatigue performance, the beam fatigue test data were analyzed through a dissipated energy approach. Basically, the 40% RAP materials were weaker than those with 30 and 50% RAP. Furthermore, traditional RAP mixes exhibit better fatigue resistance than the fractionated mixes. From the morphology aspects, the binder\u27s phase separation and physical hardening effects could explain the faster fatigue degradation of the 40% RAP binder and beam mixture subjected to the repeated loading.