A novel approach to reduce acid value of waste edible oil using nano calcium oxide and its effect on asphalt moisture susceptibility

Moisture-induced damage remains a critical challenge for asphalt pavements, particularly when bio-oils with inherently high acid values are utilized as sustainable modifiers. Conventional chemical routes for acid value reduction, while effective, are often time-consuming and have complexity for performing in real-scale scenarios, leaving a significant research gap for practical, efficient, and scalable alternatives. This study proposes a novel approach to simultaneously rejuvenate long-term aged asphalt binder (LTAB) with waste edible oil (WEO) and mitigate its acidity using nano-calcium oxide (nano-CaO), aiming to enhance binder–aggregate adhesion and moisture resistance. An optimum dosage of 6.7% WEO was determined based on penetration and softening point tests. Subsequently, nano-CaO was incorporated at 1%, 3%, and 5% dosages through two methods, including pre-mixing with WEO and post-mixing with bio-binder. Chemical analyses showed that pre-mixing nano-CaO reduced the acid value of WEO by up to 78%. WEO alone decreased asphaltenes by 23%, while pre-mixing with nano-CaO achieved a cumulative reduction of 35% relative to LTAB. High-molecular-weight species declined by up to 18%, oxidative indices by ~22%, and colloidal instability index (CII) by 37% (from 1.41 to 0.88, entering stable sol regime <0.9), confirming effective acid neutralization and colloidal stabilization. Performance evaluation revealed substantial improvements: the Moisture-Induced Shear-Thinning Index values increased by 25-35% in pre-mixed samples, while Hamburg wheel tracking tests confirmed a reduction in proportional rut depth percentage (from 30.1% to 4.9%) and more than 71.9% extension of the stripping inflection point, highlighting superior rutting and stripping resistance. Pre-mixing yielded better results than post-mixing, owing to more efficient neutralization and nanoparticle dispersion. These findings establish nano-CaO-assisted bio-oil modification as a cost-effective and sustainable pathway to reduce moisture susceptibility in asphalt binders and mixtures.