Effect of RAP Fractionation on Stiffness Behavior of Cold Asphalt Mix

This study investigates the impact of fractionating Reclaimed Asphalt Pavement (RAP) on the stiffness properties of cold asphalt mix (CAM). The RAP material was divided into fine (passing through 2.36 mm) and coarse (ranging from 19 mm to 2.36 mm) fractions, along with an unfractionated type. For each type of fractionation, four RAP dosage levels (25, 50, 75, 100%) were evaluated. CAM was prepared with the optimal emulsion content at an air void of 10 ± 1% for all 13 mix combinations. The Indirect Tensile Stiffness Modulus (ITSM) was conducted at three temperatures (15 ℃, 25 ℃, and 35 ℃) for all 13 mix combinations. The Indirect Tensile Strength (ITS) and Resilient Modulus (RM) tests were also conducted at 25℃. Based on the findings, ITSM of CAM dropped with temperature for all fractionations. Regardless of temperature, the ITSM increased with the dosage of RAP for all fractionations. Compared to coarse and unfractionated mixes, fine fractionated mixes showed a 31% and 30% reduction in stiffness, respectively. Tensile strength improved by 53% for the coarse fraction (at 100% RAP) and by 38% for the unfractionated mix (at 50% RAP), but there was no appreciable change when fine RAP was added up to 50%. The RM values improved by 24, 83, and 92% for fine, coarse, and unfractionated mixes at increasing RAP doses. This study recommends using coarse fractionation over unfractionated and fine-fractionation of RAP in CAM for better tensile strength and stiffness characteristics.