Semnan University Press Journal of Rehabilitation in Civil Engineering 2345-4415 14 3 2026 08 01 Optimizing the Amount of Multicomponent Polymer Fibers in RAP Mixtures Based on the BMD Criteria 10334 10.22075/jrce.2025.2361 EN Mahmoud Reza Keymanesh Associate Professor, North Tehran Branch, Payam Noor University Amin Jafari Department of Civil Engineering, Payame Noor University, Tehran, Iran Journal Article 2025 06 04 As the final part of a pavement, asphalt mixtures are aimed to ensure the road users’ safety and comfort and any defect in them can disturb the users. They usually consist of bitumen, aggregates and air (as main components) plus a wide range of additives, among which fibers are more important and attract the attention of researchers because they overcome the tensile weakness of asphalt mixtures and improve their performance features. This research has used multicomponent fibers to modify the properties of asphalt mixtures containing reclaimed asphalt pavement overhauled by waste, engine-oil rejuvenator, and applied the balanced mix-design method to optimize the materials. The dynamic creep test, Illinois Flexibility Index (IFI), indirect tensile strength (ITS), and tensile strength ratio (TSR) were utilized to evaluate the mixtures’ performance. The findings revealed that the incorporation of multi-component polymer fibers improved the rutting resistance of asphalt mixtures by up to 70%, whereas the addition of waste oil decreased rutting resistance by up to 1.5%. Furthermore, the highest IFI values were recorded for the specimens containing waste oil. However, the rejuvenator exhibited a negligible effect on the TSR values. Considering the Balanced Mix Design (BMD) criteria, two mixtures containing 40% reclaimed asphalt pavement (RAP), 0.75% rejuvenator, and 0.8% or 1.2% multi-component fibers were identified as the optimum mixtures in this study. https://civiljournal.semnan.ac.ir/article_10334_83995950a21a150dbcf0120ec0c9acca.pdf