Synergistic effects of graphene nanoplatelets and para-wood ash on the mechanical behavior of recycled aggregate concrete

Graphene nanoplatelets (GNP), a nanomaterial with promising engineering potential, remain underexplored in recycled construction materials. This study investigates the combined influence of GNP and para-wood ash (PWA) on the mechanical and microstructural properties of recycled aggregate concrete (RAC). Recycled concrete aggregate (RCA) replaced natural coarse aggregate at 0%, 50%, and 100%, while PWA replaced 10% of cement by volume. GNP was added at 0.015–0.060% by cement weight. Tests included compressive, tensile, and flexural strength, ultrasonic pulse velocity, and microstructural analyses with statistical and numerical evaluations. Results showed that 0.060% GNP improved 28-day compressive, tensile, and flexural strengths by 14.8%, 31.1%, and 14.3%, respectively, and increased elastic modulus by up to 45%. Although PWA and RCA individually reduced strength, their negative effects were mitigated with GNP. Microstructural analysis confirmed pore refinement and interfacial transition zone (ITZ) densification, while environmental assessment emphasized reduced cement demand and energy use, enhancing RAC sustainability.