Component-activating redesign of cold patch asphalt mixture towards humidity adaptability: Performance evaluation, structure characterization, and mechanism analysis

Conventional cold patch asphalt mixtures (CPAMs), used for pothole repair, always exist some issues in engineering performance, particularly mechanical strength, humidity adaptability, and binder adhesion. To address these concerns, this study considered using solvent naphtha (SN) as diluent and polymeric methylene diphenyl diisocyanate (PMDI) as reactive chemical at different mixing proportions, in combination with virgin bitumen, to optimally prepare highly active cold patch asphalt liquids (CPALs) for improving the overall performance of CPAMs. Based on this, the moisture-cured Marshall performance, indirect tensile fatigue resistance, as well as aging resistance of CPAMs, and the adhesion, phase structure, and molecular structure of CPALs, were systematically evaluated by a series of tests for the performance-enhancing mechanism analysis. The results demonstrated that the suitable incorporation of PMDI into CPAL can not only benefit to compensate the strength deficiency of SN-based CPAM, even under the moisture conditions, reaching mostly at 15.6 kN in Marshall load after 48 h, but also significantly extend the fatigue life, improve the aging resistance with a remaining Marshall load of 9.5 kN, at a SN-to-PMDI ratio of 50:50. Furthermore, the adhesion of asphalt binder to aggregates was enhanced after introducing PMDI, with a binder mass loss decreased from 17.31 % to 12.24 %. In addition, PMDI can suppress the agglomeration of SN in CPAL to achieve more uniform distributions, which can provide –NCO groups to react with gaseous water and –OH groups from aggregates to enhance the binder adhesion and mixture performance during mixing and after paving. Overall, the proposed approach can provide a promising solution to address the long-term application concern of CPAM in pothole repairing. • Polymeric methylene diphenyl diisocyanate (PMDI) and solvent naphtha (SN) were used to prepare cold patch asphalt liquids (CPALs) for cold mixtures (CPAMs). • Both use of PMDI and SN can enhance Marshall load, fatigue life, aging resistance, and binder adhesion of CPAM, due to chemical reactions. • The proposed innovative method can greatly contribute to extending the service duration of CPAM in pavement surface recovery.