Experimental evaluation of asphalt binder with lignin-rich black liquor and waste engine oil additives

Abstract

Conventional binders used in flexible pavements often suffer from rutting at high temperatures and cracking under ageing. Polymer modifiers can improve performance but are costly and environmentally demanding. To address these limitations, this study investigates the combined use of black liquor (BL), a lignin-rich by-product of the pulp industry and waste engine oil (WEO) as waste derived modifiers for VG 30 bitumen. In this work, VG 30 was modified with 10–30% BL and 3–12% WEO, and tested for physical, chemical and rheological performance. BL increased binder stiffness and thermal stability, while WEO improved flexibility and reduced brittleness; their combined use produced a balanced viscoelastic response, with blends containing 20–30% BL and 6–9% WEO showing optimal rutting resistance and elasticity. The 30% BL + 9% WEO blend achieved a high-temperature grade of PG 76 and exhibited lower non-recoverable creep compliance (J_nr) than neat VG 30 when tested at the same temperature, indicating improved rutting resistance, while maintaining 55% elastic recovery. FTIR analysis confirmed that modification occurs primarily through physical blending. A TOPSIS-based multi-criteria decision analysis (MCDA) identified 30% BL + 9% WEO as the most suitable formulation for hot, heavy-traffic conditions, and 20% BL + 9% WEO for moderate climates. A screening-level cradle-to-gate life cycle assessment indicated that partial replacement of bitumen with BL and WEO can reduce greenhouse gas emissions and energy demand. Overall, BL–WEO modification provides a low-cost and environmentally favorable alternative to polymer-modified binders while maintaining strong high-temperature performance.

Graphical abstract

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