A novel self-curing active cold patch asphalt mixture: Performance evaluation and mechanism analysis

Cold patch asphalt mixtures (CPAMs) are increasingly favored for pothole repairs in asphalt pavements due to their environmental benefits and ease of construction. However, their low strength and durability have hindered broader application, necessitating the development of CPAMs with enhanced engineering performance. To address these challenges, this study proposes a novel self-curing active CPAM incorporating solvent naphtha (SN) as a diluent and polymerized methylene diphenyl diisocyanate (PMDI) as a polymer modifier. Various SN-to-PMDI ratios and SN-PMDI contents relative to virgin bitumen (VB) were evaluated to produce cold patch asphalt liquid (CPAL) and the corresponding CPAMs. Viscosity tests confirmed that SN effectively reduces VB viscosity, ensuring its workability. Specifically, adding 10 % SN reduced VB viscosity by approximately 30 %, while higher SN content (e.g., 30 %) significantly compromised mechanical performance. Mechanical evaluations, including Marshall stability, moisture susceptibility, crack resistance, freeze-thaw resistance, and rutting resistance, demonstrated that CPAM containing 20 % SN-PMDI with a 50:50 SN-to-PMDI ratio achieved excellent mechanical performance comparable to hot mix asphalt (HMA). Mechanism analysis through FTIR tests further revealed that PMDI reacts with atmospheric moisture, transforming isocyanate groups (-NCO) into carbamate groups (-NHCOO), and also interacts with hydroxyl groups on limestone aggregates, forming carbamate compounds, which contribute to a 20 % increase in strength development. Overall, this study introduces a novel approach for preparing high-performance CPAM, providing a promising solution for durable and efficient pothole repairs in practical engineering applications.