Harnessing methane-derived nanocarbon coatings on steel slag for high-performance cementitious composites

Nano-modification technologies open new pathways for developing lower-carbon cementitious materials. However, the widespread application of carbon nanomaterials in practical engineering is constrained by their high cost, complex fabrication processes, and difficulties in dispersion within cementitious composites. This study proposes an in-situ nano-carbon deposition method based on methane catalytic cracking, utilizing steel slag as a substrate to fabricate nano-carbon coated steel slag composites (DNCCSS). The results demonstrate that at a deposited nanocarbon dosage of 0.15 wt.% relative to cement, DNCCSS-modified mortar exhibits a flexural and compressive strength enhancement of about 15.0-17.6% compared to the plain SS group mortar. Microstructural analysis reveals that DNCCSS significantly optimizes the pore structure through the nucleation and pore infilling effects, reducing cumulative porosity by 9.3-10.5%. Molecular dynamics simulations reveal that DNCCSS enhances interfacial toughness via crack bridging and stress transfer. Among four simulated nanocarbon morphologies (flat, rippled, self-adhered, and collapsed), the collapsed configuration delivers the optimal toughening performance, increasing fracture energy by 14.7-42.2%. Within the cradle-to-gate boundary, life cycle assessment confirms that compared to the reference mortar, DNCCSS reduces greenhouse gas emissions and primary energy demand per unit compressive strength by 23.2% and 18.0%, respectively, while achieving cost parity with plain mortar and a cost reduction of up to 39% compared to graphene oxide modification. The findings of this study not only advance the fundamental understanding of nano-carbon reinforcement in cementitious composites, but also demonstrate the potential of DNCCSS as an economical and environmentally favorable strategy for steel slag valorization and the development of lower-carbon cementitious materials.