Waste soybean oil as eco-rejuvenator for aged asphalt: VOC emission suppression, rheological regeneration and colloidal microstructure mechanism

Recycling waste asphalt is increasingly important amid growing highway maintenance demands and environmental concerns, yet volatile organic compound (VOC) emissions during recovery remain poorly understood. This study investigates how waste soybean oil (WSO) affects VOC emissions and regeneration properties of aged 70# asphalt. WSO was blended at 4%, 6%, 8%, and 10% concentrations and characterized by way of gas chromatography–mass spectrometry, Fourier transform infrared (FTIR), and gel permeation chromatography. Rheological performance was evaluated using a dynamic shear rheometer (high-temperature) and bending beam rheometer (low-temperature), with microstructure observed by atomic force microscopy (AFM). Results show WSO significantly reduces VOC emissions – 8% WSO achieves a 33.23% reduction against unmodified asphalt, with notable decreases in toxic aromatics and sulfur-containing compounds. Molecular analysis revealed WSO replenishes light and aromatic components, restoring colloidal stability to 92% of unaged asphalt while inhibiting oxygen- and sulfur-containing compound formation. Performance tests showed that 8% WSO provides high-temperature rutting resistance comparable to new asphalt and reduces low-temperature creep stiffness to 46.9% of aged asphalt, improving crack resistance. AFM confirmed that WSO alleviates asphalt aggregation and optimizes colloid structure. Therefore, 8% WSO is the optimal dosage, achieving the best balance between VOC inhibition and regeneration performance.