Enhancing the performance of grafted polymer-modified binders and Stone Mastic Asphalt (SMA) mixtures: A comprehensive experimental evaluation

The incorporation of polymers into bitumen to enhance the performance and durability of asphalt pavements has received increasing attention in recent years. However, conventional polymers often suffer from phase incompatibility, separation tendencies, and poor dispersion within the bitumen matrix. To overcome these limitations, maleic anhydride-grafted polymers have emerged as promising modifiers for improving bitumen properties. This study investigates the effects of four polymers—polypropylene (PP), linear low-density polyethylene (LLDPE), maleic anhydride-grafted polypropylene (MAH-g-PP), and maleic anhydride-grafted linear low-density polyethylene (MAH-g-LLDPE)—incorporated into base bitumen at four dosage levels (0 %, 3 %, 5 %, and 7 % by weight). The evaluation was conducted at both the binder and mixture levels. Binder performance was assessed through penetration, softening point, rotational viscosity, phase separation, and elastic recovery tests. The performance of Stone Mastic Asphalt (SMA) mixtures was evaluated using resilient modulus, Hamburg wheel tracking, four-point bending fatigue, tensile strength ratio (TSR), and the Illinois Flexibility Index (FI) tests. Statistical analyses were conducted using ANOVA and Pearson correlation in SPSS. The results demonstrated that grafted polymers, especially MAH-g-LLDPE, significantly outperformed conventional polymers. The mixture containing 7 % MAH-g-LLDPE (LLDG7) exhibited the highest elastic recovery (38.9 %), the lowest phase separation, the highest TSR value (87.6 %), a 154 % increase in the flexibility index, and a 21.4 % improvement in fatigue life compared to the control. The statistical results also revealed that the type, content, and structure of the polymer had significant effects on both binder and mixture performance. Moreover, strong correlations were observed between certain binder properties and asphalt mixture performance indices, highlighting the importance of appropriate polymer selection in designing sustainable and high-performance asphalt mixtures.