Investigating the Relationship between the Fatigue Cracking Resistance and Thermal Characteristics of Asphalt Binders Extracted from Field Mixes Containing Recycled Materials

Asphalt components have a significant contribution to the fatigue cracking resistance of asphalt mixes. Softer asphalt binders, characterized through the Superpave grading system, resist fatigue cracking more than stiffer binders. During the long-term aging, the binders’ components changed from lower- to higher-molecular-weight constituents that increased binders’ stiffnesses. Using recycled materials in the mixes increases the stiffnesses of the binders inside these mixes by altering the binders’ components. The binders were extracted and recovered (E & R) from field mixes containing different percentages of recycled materials [reclaimed asphalt pavement (RAP) and recycled asphalt shingles] and binders’ performance grades. The fatigue resistance of the E & R binders was evaluated using the Superpave fatigue cracking parameter and the number of load repetitions to failure. Thermal characterization of the E & R binders reflected the binders’ thermal degradation based on their components. The Fourier transform infrared (FTIR) indices were investigated to confirm the changes in the fatigue resistance and thermal characterization results between different binders. The binders E & R from the newest mixes and contained softer binder showed the highest resistance to fatigue cracking and the lowest onset temperatures. However, these mixes contained 30% asphalt binder replacement by RAP. The derivative of thermograph for these binders presented more than one peak; this indicated the existence of the low-molecular-weight fractions that were responsible for enhancing the fatigue resistance. These binders presented the lowest aging condition by showing the lowest aromatics, carbonyl, the highest aliphatics, and sulfoxide FTIR indices