Rheological Evaluation of Bitumen Modified With Polyethylene and Crumb Rubber via the Multiple Stress Creep Recovery (MSCR) Test: A Case Study

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Abstract
Conventional polymer modification of bitumen, while enhancing in‐service performance, often leads to increased material costs. Recycled tire‐derived crumb rubber (CR) presents a sustainable and economically viable alternative, offering valuable elastomeric properties and environmental benefits by diverting waste from landfills. However, optimizing CR dosages and balancing its synergy with secondary polymer additives remains a critical challenge, necessitating further research to establish standardized blending ratios that maximize cost‐performance efficiency without compromising viscoelastic properties under diverse climatic and traffic conditions. This study addresses this challenge by investigating the high‐temperature rheological properties of polymer‐modified bitumen (PMB) using the multiple stress creep recovery (MSCR) test. This robust methodology provides crucial insights into the material behavior of PMB, directly supporting the selection and development of sustainable road infrastructure. The investigation assessed the rutting resistance of four bitumen formulations at 64°C: unmodified bitumen, bitumen modified with 3% (by weight of bitumen) polyethylene (PE), 3% CR, and a combined blend of 3% PE + 3% CR. Tests were conducted at two critical stress levels (0.1 and 3.2 kPa). The findings demonstrate that the PMB sample containing both 3% CR and 3% PE exhibits superior elastic recovery and significantly reduced nonrecoverable creep compliance (Jnr) across both stress levels, indicating its enhanced resistance to permanent deformation. MSCR results showed that at 0.1 kPa, recovery increased from 2% in the unmodified binder to 10.5% with PE, 4% with CR, and 22.3% with the combined PE + CR; at 3.2 kPa, the CR + PE blend maintained 5% recovery with a Jnr of 1.63 kPa −1 , outperforming PE (Jnr 5.35 kPa −1 ) and CR (Jnr 2.94 kPa −1 ). This superior performance confirms the stress‐dependent behavior of PMBs, with the combined 3% CR + 3% PE blend showing the greatest improvement in rutting resistance. Statistical analysis indicates that 3% PE is suitable for standard traffic, while the CR + PE blend is preferable for heavy traffic, providing practical recommendations for performance‐grade (PG) specifications.

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