Assessment of Strength and Stability in Cold Asphalt Mixtures Reinforced with 0.20% and 0.25% Polypropylene Microfibers

Introduction. The incorporation of new materials and technologies has opened avenues for research in asphalt mixtures. Various studies have focused on modifying conventional manufacturing methods by replacing or enhancing traditional components. Among these, synthetic polypropylene microfibers have been investigated as partial substitutes for mineral aggregates. Objectives. This study aimed to evaluate the indirect tensile strength and stability of cold asphalt mixtures reinforced with 0.20% and 0.25% polypropylene microfibers. Materials and Methods. A reference cold asphalt mixture (sand-asphalt) was prepared following the Hubbard-Field method. Two modified mixtures were produced by replacing a proportion of the aggregate with 0.20% and 0.25% microfibers by volume. The index properties of the modified mixtures were assessed and compared to the reference mixture. Indirect tensile strength tests were also conducted. Results. The incorporation of polypropylene microfibers increased stability under ambient conditions by up to 21% and improved indirect tensile strength by approximately 100% compared to the reference mixture. Compatibility and reduction of air voids were also enhanced. However, swelling increased notably at 0.25% microfiber content, exceeding specification limits, while water absorption remained within acceptable ranges. Conclusions. Reinforcing cold asphalt mixtures with polypropylene microfibers resulted in significant improvements in stability, compaction, and tensile strength without compromising essential performance criteria.