Citation: Nciri, N.; Kim, N. Upcycling Discarded Shoe Polish into High Value-Added Asphalt Fluxing Agent for Use in Hot Mix Paving Applications. Materials 2022, 15, 6454. https://doi.org/10.3390/ma15186454 Academic Editor: Grzegorz Mazurek Received: 2 August 2022 Accepted: 14 September 2022 Published: 17 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Upcycling Discarded Shoe Polish into High Value-Added Asphalt Fluxing Agent for Use in Hot Mix Paving Applications Nader Nciri 1,2 and Namho Kim 1, * 1 School of Industrial Design & Architectural Engineering, Korea University of Technology & Education, 1600 Chungjeol-ro, Byeongcheon-myeon, Dongnam-gu, Cheonan 31253, Chungnam, Korea 2 School of Energy, Materials & Chemical Engineering, Korea University of Technology & Education, 1600 Chungjeol-ro, Byeongcheon-myeon, Dongnam-gu, Cheonan 31253, Chungnam, Korea * Correspondence: nhkim@koreatech.ac.kr; Tel.: +82-41-560-1332 Abstract: This research effort is geared towards revealing the latent potential of discarded shoe polish that might be repurposed as an asphalt fluxing agent for the construction of durable and sustainable road surfaces. To drive this creative invention, the effect of various proportions of waste shoe polish (e.g., 5, 10 and 15 wt. % WSP) on the performance of base AP-5 bitumen was inspected in great detail. A meticulous investigation of the chemical, physical, and rheological properties of the resultant combinations was carried out using a variety of state-of-the-art laboratory techniques, specifically: thin-layer chromatography-flame ionization detection (TLC-FID), Fourier transform-infrared spectroscopy (FT-IR), needle penetration, ring-and-ball softening point, Brookfield viscometer, ductility, flash/fire points, dynamic shear rheometer (DSR), multiple stress-creep recovery (MSCR), and bending beam rheometer (BBR) tests. The Iatroscan data disclosed that the continuous feeding of binder with WSP had a minor impact on SARA fractional distribution, regardless of aging. According to the FT-IR scan, the stepwise addition of WSP to the binder did not result in any significant chemical alterations in the blends. The combined outcomes of the DSR/BBR/empirical test methods forecasted that the partly bio-sourced additive would greatly improve the mixing– compaction temperatures, workability, and coating–adhesion properties of bituminous mixtures while imparting them with outstanding anti-aging/cracking attributes. In short, the utilization of waste shoe polish as a fluxing agent for hot asphalt mix production and application is not only safe, feasible, and affordable, but it has the potential to abate the pollution caused by the shoe-care market while simultaneously enhancing the overall performance of the pavement and extending its service lifespan. Keywords: hot mix asphalt; discarded shoe polish; fluxing agent; TLC-FID; FT-IR; empirical tests; flash point; DSR; MSCR; BBR 1. Introduction The lifespan of paved roadways is chiefly dependent upon certain definite factors; some of them are external and some others are internal. The external factors that may affect the performance of a given pavement cover mechanical (i.e., traffic loading) and climatic factors such as air, sunlight, heat, water, and others, whereas the internal factors entail the composition of the entire block constituting the road pavement, such as rocky aggregates (e.g., crushed gravel/stone, 85 wt. %), gummy binder (i.e., glue, 10 wt. %), and voids (5 wt. %), etc. [1]. Owing to its vital role that it plays in sustaining the entire structure and function of bi- tuminous concrete surfaces, asphalt cement is regarded as one of the main key components that governs both the bearing capacity and durability of a given roadway. Over time, the binder steadily ages and loses its engineering assets, resulting in several dramatic issues ranging from permanent deformation (e.g., corrugations, rutting, shoving) to cracking (e.g., reflective, thermal, fatigue), etc. [2]. Materials 2022, 15, 6454. https://doi.org/10.3390/ma15186454 https://www.mdpi.com/journal/materials