Evaluating the Effect of Crumb Rubber Particle Sizes and Proportions on the Performance of Reclaimed Asphalt Mixture
Volume 12 , Issue 1 , December 2025 , Pages 57-73
Authors
Khazan Baqi Mohammed Salih 1 ; Hardy Kamal Karim Karim 2
1 University of Sulaymaniyah, Civil Engineering Department
2 University of Sulaimani , College of Engineering , Civil Engineering Department
10.17656/sjes.102002
Keywords
Abstract
This study investigated the effects of various sizes and proportions of CR into environmentally friendly asphalt mixtures containing 35% RAP. CR particles retained on sieves #30, #50, #100, #200, and the pan were added at 2%, 4%, and 6% by weight of the binder. Mixture performance was evaluated in terms of rutting (Kim test), moisture sensitivity, fatigue (SCB test), and stripping resistance. Both RAP and virgin aggregates met all specification requirements. Although the RAP binder (PG 70-10) was stiffer and more brittle than the virgin binder (PG 70-22), its properties remained within acceptable limits for new asphalt mixtures. Volumetric analysis showed all CR-modified mixtures met Superpave criteria, with coarser CR increasing binder demand and finer CR yielding denser mixtures. CR on sieve #200 provided the highest rutting resistance, with 2% and 4% significantly reducing rut depths, whereas 6% showed no statistically significant improvement. Coarser (#50) and pan-sized CR generally increased rutting, acting primarily as filler. CR had a minor and mostly insignificant effect on ITS, with most mixtures maintaining ITSR values above 80%, except for 4% and 6% of #50 and #200 CR. In SCB tests, only #50 and #200 CR improved fracture resistance, significantly increasing the strain energy release rate (Jc) at 2–6% dosages. Stripping tests indicated that 4–6% #30 CR and 2–4% pan-sized CR improved moisture resistance, while most other sizes slightly exceeded acceptable limits. Overall, the rutting, moisture, fatigue, and stripping resistance of reclaimed asphalt mixtures were significantly affected by CR size and content.