Durability assessment of cellulose nanocrystal-modified hot mix asphalt under oxidative aging and freeze–thaw conditioning: mechanical and FTIR-based evaluation

This study investigates the durability of cellulose nanocrystal (CNC)-modified hot mix asphalt (HMA) subjected to oxidative aging and freeze–thaw (F–T) conditioning through an integrated chemical and mechanical evaluation. The research aims to clarify the influence of CNC on asphalt binder oxidation and the low-temperature performance of asphalt mixtures under combined environmental deterioration. Fourier transform infrared spectroscopy (FTIR) was employed to quantify oxidative aging using carbonyl and sulfoxide functional group indices, while fracture energy (G f ) and fracture toughness (K IC /K IIC ) were determined using semi-circular bend (SCB) tests conducted at 0, − 10, and − 20 °C under Mode I and Mode II loading. In addition, empirical predictive models were developed to estimate fracture properties as functions of CNC dosage, temperature, loading mode, aging condition, and F–T exposure. FTIR analysis demonstrated that oxidative aging substantially increased the carbonyl and sulfoxide indices of the unmodified asphalt binder, whereas CNC modification effectively suppressed oxidation, resulting in a 66% reduction in carbonyl index development relative to the control binder. Mechanical evaluation showed that CNC significantly enhanced the low-temperature resistance of HMA to crack initiation and propagation, with mixtures containing 1% CNC exhibiting the most balanced overall performance. Although the applied F–T conditioning reduced fracture energy and fracture toughness for most mixtures, CNC-modified mixtures generally exhibited improved retention of these properties, indicating greater resistance to the initial effects of freeze–thaw conditioning under the investigated laboratory conditions. Under combined aging and F–T conditioning, aged mixtures exhibited higher fracture energy but lower fracture toughness, suggesting different responses of energy absorption capacity and crack initiation resistance after environmental conditioning. The proposed empirical models provided satisfactory prediction of fracture energy and fracture toughness within the investigated experimental conditions, with average prediction errors of approximately 18% and 5%, respectively. Overall, the findings demonstrate that cellulose nanocrystals enhance the chemical stability of hot mix asphalt and improve its resistance to the investigated environmental conditioning, including oxidative aging and the initial effects of freeze–thaw exposure. The combined chemical–mechanical evaluation presented in this study provides a comprehensive framework for assessing the long-term durability of sustainable asphalt mixtures intended for cold and moisture-susceptible environments.