Unravelling thermal conduction mechanisms in microwave-cured cement-based composites: Transform from phonon- to electron-based conduction channels driven by nano carbon black

Microwave curing offers energy-efficient concrete treatment, but inherent thermal non-uniformity causes microstructural deterioration and potential explosion due to phonon-dominated thermal conduction. This study introduces nano carbon black (nCB) to construct electron-based conductive pathways for enhancing thermal uniformity, while clarifying the synergistic microwave-hydration mechanisms. The incorporation of nCB improved microwave absorption and constructed thermal channels within concrete, thereby promoting uniform heat distribution and increasing early-age strength by ∼70 %. Moreover, nCB-optimized microwave curing accelerated hydration, promoting C-S-H gel polymerization and modifying crystalline phases like ettringite and portlandite. Multiphysics simulations demonstrated that suitable nCB content enhanced microwave thermal conduction through constructed thermal channels, despite the inherent non-uniformity of electromagnetic fields. The dominant thermal conduction mechanism shifted from phonon- to electron-based conduction by incorporating nCB, driven by synergistic effects of dipole polarization, interfacial polarization, and conduction loss. This work offers a new strategy for optimizing microwave-curing behavior through nanoscale thermal design in cement-based composites.