Comparative analysis of low-temperature cracking resistance in Uzbekistan bitumens using bending beam rheometry

Abstrak

Low-temperature thermal cracking is a primary distress mechanism in asphalt pavements exposed to extreme continental climates. This study conducts a comparative rheological evaluation of standard and modified bituminous binders to assess their low-temperature fracture resistance within the context of Uzbekistan’s pavement infrastructure. Four binder formulations were investigated: a conventional unmodified petroleum bitumen (BND), a polymer-modified bitumen (PMB), a crumb rubber-modified bitumen (CRMB), and a sulfur-modified bitumen (SMB). To replicate in-service thermo-oxidative degradation, all binders underwent sequential short-term and long-term aging via the Rolling Thin Film Oven Test (RTFOT) and Pressure Aging Vessel (PAV), respectively. Low-temperature viscoelastic behavior was quantified using a Bending Beam Rheometer (BBR) at isothermal test temperatures of [-12°C, -18°C, and -24°C]. The critical rheological parameters—creep stiffness, S(60), and the stress relaxation rate, m(60)—were analyzed to establish the continuous low-temperature Performance Grade (PG) limits for each binder. Experimental results reveal that the modifier type fundamentally dictates the thermo-rheological susceptibility of the binders post-aging. Specifically, the PMB and CRMB formulations exhibited enhanced resistance to thermal embrittlement, maintaining lower stiffness gradients and superior stress relaxation capacities relative to the unmodified BND. Ultimately, these findings offer a fundamental mechanistic basis for optimizing binder selection in Central Asia, facilitating the regional transition from empirical grading specifications toward advanced performance-based methodologies.