Asphalt binder, a byproduct of oil refining, needs further treatment to improve its characteristics for paving purposes. This research focuses on the formulation of modified asphalt binders using locally obtained additives, evaluating their characteristics via standardized testing, and verifying adherence to paving specifications. The study investigated the use of crumb rubber derived from automobile tires as an addition in 40–50 grade asphalt cement. Three distinct concentrations of crumb rubber (5%, 10%, and 15%) were included, with the mixture being constantly agitated and heated at 180 ℃ for 90 min to assess its performance. Asphalt binder obtained from the Al-Sahil Refinery in northern Iraq was chosen for modification and characterization. The altered samples were subjected to testing to evaluate physical parameters including penetration, ductility, softening point, and rotational viscosity before to and after the incorporation of modifiers. The results shown that penetration values decreased by 25.5%, 39.5%, and 53.4% with the incorporation of crumb rubber at 5%, 10%, and 15%, respectively. Ductility values decreased by 21.3%, 32.0%, and 37.8%. In contrast, the softening point elevated by 9.4%, 16.9%, and 26.4%, whereas rotational viscosity increased at all examined amounts at 135 ℃.