Synergistic Interfacial Regulation by Nano‐TiO 2 and Carboxylated Cellulose Nanofibers for Multiscale Surface Stabilization of Cementitious Composites

In this study, a composite‐modified cementitious system incorporating nano‐TiO 2 and carboxylated cellulose nanofibers (CCNF) was developed to unveil the synergistic mechanism between point‐like nucleation induced by nano‐TiO 2 and interface‐induced deposition regulated by CCNF, and to establish its relationship with surface stability, pore structure, and ion transport behavior. The results show that in a highly alkaline and Ca 2+ ‐rich pore environment, the carboxyl groups on CCNF are interfacially activated and promote the local accumulation of Ca─Si─O‐rich species along fibre‐associated interfaces, while nano‐TiO 2 provides heterogeneous nucleation sites for hydration‐product precipitation. The coupled effects of nano‐TiO 2 and CCNF promote a more continuous spatial distribution of hydration‐product‐rich regions and reduce the continuity of local low‐density defects. A cross‐scale surface‐damage assessment combining macroscopic roughness (Ra) and AFM‐based nanoscale roughness (Sq) was further employed to distinguish surface geometric smoothing from local nanoscale damage accumulation. The C0.2T1 system exhibited an approximately 62.5% increase in 28‐day compressive strength. These improvements do not arise from the formation of new dominant hydration products or a substantial increase in overall hydration but are primarily associated with the spatial reorganization of hydration products, refinement of the pore‐structure, reduction of low‐density defective regions, and modification of ion transport pathways.