Dimensional engineering of fly ash-grown carbon nanomaterials for sustainable cement reinforcement

Global solid waste management and construction material sustainability converge in fly ash (FA), with approximately 1700 million tons generated annually, while current utilization fails to adequately address its environmental burdens. This work establishes an ecomaterials paradigm by synthesizing controllable-sized carbon nanomaterials in situ on FA, converting FA into high-performance cement reinforcement materials. Through chemical vapor deposition, planar graphene is grown via intrinsic oxide catalysis and tubular carbon nanotubes on iron-functionalized FA, creating catalyst-integrated composites that eliminate purification steps and dispersion challenges. The substrate-bonded nanomaterials drastically reduce production costs compared to commercial alternatives while ensuring optimal distribution in cementitious systems. These solid waste-derived ecomaterials function as multifunctional additives at dosages of 5%–20%, reducing dependence on virgin cement while delivering complementary performance enhancements: graphene provides exceptional early-age enhancement (+36.96% flexural strength at 3 d in mortar, +18.55% compressive strength at 7 d in concrete), whereas carbon nanotubes provide sustained reinforcement maintaining advantages through 28 d across both mortar and concrete systems. This catalyst-integrated approach simultaneously addresses solid waste accumulation, reduces cement-related emissions, and delivers superior material performance compared to conventional alternatives, demonstrating a scalable pathway for solid waste valorization through dimensional engineering of carbon nanomaterials.