A novel approach to reduce acid value of waste edible oil using nano calcium oxide and its effect on asphalt moisture susceptibility
Mohammad Hossein Hassanjani, Mahyar Arabani, Fereidoon Moghadas Nejad, Mousa Andarz Jadehkenari
Abstract
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.