Modification mechanism and enhanced low-temperature performance of asphalt mixtures with graphene-modified phase-change microcapsules

• CGMFPCM combined the properties of CG and PCM. • Suitable CG doping simultaneously enhanced the thermal stability and thermal efficiency of PCM. • CGMFPCM reduced the temperature sensitivity of asphalt. • CGMFPCM improved the low-temperature characteristics of asphalt. This study explored the modification mechanism of adding commercial graphene (CG) to microcapsule wall materials of the prepared modified phase-change microcapsules (MFPCM) and the modified asphalt. To this end, different amounts of CG and melamine formaldehyde (MF) resin were used as microcapsule wall materials (with n- tetradecane as the core material) to prepare graphene-modified phase-change microcapsule (CGMFPCM) specimens. The microstructure and properties of MFPCM specimens with different contents of CG were also characterized via a differential scanning calorimeter (DSC), simultaneous thermal analyzer, scanning electron microscope (SEM), and Fourier-transform infrared (FT-IR) spectrometer. Next, the asphalt specimens modified by n- tetradecane, MFPCM, and CGMFPCM with different contents were prepared by the high-speed shearing method. The conventional performances of the modified asphalt specimens were assessed via penetration, softening point, and ductility tests, while their microstructure and performance were investigated by SEM, FT-IR spectrometer, and DSC. The thermodynamic characteristics of both base and modified asphalt specimens were measured via a conductometer. No chemical reactions between the added CG and core or wall materials of MFPCM were revealed. After adding CG, CGMFPCM specimens combined high heat conductivity of CG and phase change performance of MFPCM. Adding 0.45% CG to MFPCM enhanced its thermal efficiency without harming its thermal stability. The modification of base asphalt by phase-change materials was reduced to its physical modification, implying that phase-change materials were simply dispersed in the base asphalt with no chemical reactions. High-temperature heating and high-speed shearing in the preparation of modified asphalt reduced the effective content of phase-change materials. Both microscopic and macroscopic test results confirmed that the low-temperature performance of asphalt was improved after adding CGMFPCM.