Surface treatment of waste tire rubber via oxidation and alkalization for enhanced compatibility with bitumen

The accumulation of waste tires poses critical environmental and engineering challenges. Incorporating waste crumb rubber (WCR) into asphalt pavements enhances recycling and pavement performance, yet limited compatibility between WCR and bitumen remains a constraint. This study explores surface treatments using hydrogen peroxide (H 2 O 2 ) and sodium hydroxide (NaOH) under varying intensities. Microscopic analysis (scanning electron microscopy (SEM), specific surface area (SSA), contact angle, and Fourier transform infrared (FTIR) spectroscopy) and macroscopic evaluations (striping rates by modified boiling test) on coarse WCR, and storage stability test on rubberized binders reveal that both treatments enhance interfacial adhesion and compatibility through surface etching and polar group incorporation. Within 2 mol/L, H 2 O 2 treatment becomes increasingly effective with higher concentration and temperature, whereas NaOH solutions exceeding 15 % at elevated temperatures cause excessive corrosion without further interfacial improvement. Unexpectedly, both treatments may induce the micro-swelling effect, modifying WCR viscoelasticity, with NaOH exhibiting a more pronounced impact. Overall effects of H 2 O 2 and NaOH treatments on WCR (schematic) • H 2 O 2 and NaOH treatments enhance compatibility and adhesion between bitumen and waste rubber. • Surface morphology and polarity of waste rubber are improved, resembling an etching effect. • Macro-micro analyses confirm chemical changes and enhanced interfacial bonding. • Treatment intensities are systematically compared to evaluate performance and side effects.