Impact of sustainable modifications on the rheological properties of bitumen

The growing emphasis on sustainability and performance in modern asphalt pavements arises from durability challenges and environmental concerns. This study explores the rheological, mechanical, and thermal characteristics of 40/50 penetration-grade bitumen modified with SBS, WCO, and ABA additives in proportions of 4-5% SBS, 3-4-5% WCO, and 4-5-6% ABA. Comprehensive performance evaluations utilized advanced rheological tests, including the G-R Index, Storage and Loss Modulus, Complex Viscosity, Loss Factor (tan δ), Phase Angle, Complex Shear Modulus (G*), Cole-Cole Plot, Linear Amplitude Sweep (LAS), and VECD models. The G-R Index revealed that SBS and ABA significantly bolstered resistance to high temperatures, with G*/sin δ peaking at 5.306 kPa for 5% SBS and 3.655 kPa for 4% ABA at 76°C. Conversely, WCO increased flexibility but compromised rutting resistance, showing a peak G*/sin δ of 13.300 kPa at 52°C for 3% WCO. Storage modulus (G′) analysis highlighted superior stiffness in SBS-modified bitumen (3,428 Pa at 5% SBS) and moderate improvements with ABA, whereas WCO improved ductility but reduced stiffness. Optimal complex viscosity was achieved with SBS and ABA modifications, particularly at 5% SBS and 6% ABA. WCO-modified bitumen showed reduced viscosity, which favored flexibility. Supporting these results, tan δ values for SBS-modified samples indicated enhanced viscoelasticity (0.12 for 5% SBS), while WCO showed higher viscous behavior (>0.3). Phase angle (δ) analysis reflected elastic properties in SBS and ABA samples, with WCO exhibiting more viscous responses. The complex shear modulus (G*) peaked at 6.87 MPa for 5% SBS and was moderate for ABA (3 MPa), while WCO exhibited lower stiffness. LAS and VECD testing confirmed superior fatigue resistance and delayed damage progression for SBS and ABA, though WCO samples showed limited durability. Cole-Cole plots demonstrated greater homogeneity in SBS and ABA samples, while WCO emphasized flexibility and performance at low temperatures. In conclusion, 5% SBS and 6% ABA formulations delivered optimal stiffness, elasticity, and fatigue resistance under high-stress conditions. In contrast, 3% WCO provided superior flexibility for applications in low-temperature environments. These findings underscore the potential of eco-friendly, balanced bitumen designs for enhanced pavement performance across varied conditions.