Engineering a Multi-Dimensional Thermally Conductive Network to Enhance the Thermo-Mechanical Stability of Concrete

Reliable thermo-mechanical performance is typically required in intensive thermal management applications, such as thermal energy storage systems and concrete-structured data centers; however, there is usually a trade-off between thermal conductivity and strength when designing thermally conductive concrete. To address the critical demand for concrete that combines high thermal conductivity with excellent structural stability after thermal loading, a novel multi-dimensional thermally conductive network was constructed by incorporating one-dimensional steel fibers and two-dimensional graphite-modified recycled aggregates to form a synergistic composite (SFRHCC). Results demonstrate that the thermal and mechanical stability of SFRHCC subjected to 200 °C was substantially improved compared with the unmodified reference. Specifically, after thermal treatment at 200 °C, SFRHCC restricted its thermal conductivity loss to only 7.6%, in stark contrast to the 28.2% reduction observed in ordinary recycled aggregate concrete (RAC). Furthermore, SFRHCC retained 92.0% and 91.3% of its reference compressive and splitting tensile strengths, vastly outperforming the unmodified reference (which retained only 75.0% and 72.4%, respectively). Both X-ray computed tomography (X-CT) and Euclidean distance transform (EDT) characterizations elucidate a high-density linear-planar overlapping network with an overall spatial connectivity of 9.94%, where the soft graphite coating layer accommodates thermal mismatch deformations and restricts volumetric fluctuations. This structural integrity effectively transforms the interfacial failure mode from simple weak-interface debonding to cohesive matrix tearing. These findings offer a promising materials design strategy for developing structural-functional integrated concrete for thermal management applications.