Response Surface Modelling and Multi-Objective Optimisation of Asphalt Binder and Mixture Properties Modified with Reclaimed Automotive Lubricants and Waste Glass Bottle Powder

Abstract

Large volumes of reclaimed automotive lubricant (RAL) and waste glass bottle powder (WGBP) are disposed of inappropriately, causing serious environmental concerns. Furthermore, the paradigm shift towards sustainability in the pavement industry has prompted academics to investigate alternatives to conventional materials. As a result, one possible approach is to use these waste products as alternative materials in the asphalt pavement sector. This study investigated the combined use of RAL and WGBP as complementary modifiers, extending beyond the conventional single-modifier approaches reported in previous studies. Thus, in this study, response surface methodology (RSM) was utilised to optimise and predict the synergistic effects of RAL as an asphalt binder replacement (0–10%) and WGBP (0–4%) as sustainable modifiers incorporated into 60/70 penetration grade asphalt binders. The responses evaluated were the binder's penetration, softening point, and specific gravity. Additionally, the mixture performance indicators include Marshall stability, flow, indirect tensile strength, the indirect tensile strength ratio, and Cantabro loss. The results demonstrate that the synergy of RAL and WGBP improves both conventional asphalt binder properties and asphalt mixture performance properties. The RSM developed statistically significant models, with key responses exhibiting high coefficients of determination (R2 > 0.93), indicating strong predictive capability and low variance. Additionally, the RSM multi-objective optimisation revealed that the contents for performance improvement and optimal workability were 1.39% RAL and 3.6% WGBP. This shows the feasibility of using both liquid and solid wastes as complementary modifiers and providing a statistically sustainable developed asphalt pavement.