Synthesis of Carbon Nanotubes on Active Silica for Enhanced Cementitious Mortars

The incorporation of carbon nanotubes (CNT) into cementitious composites has shown strong potential for enhancing mechanical performance. However, conventional dispersion methods, such as ultrasonication and chemical functionalization, are costly, complex, and difficult to scale for construction applications. This study introduces an alternative approach based on the in situ synthesis of CNT on active silica grains, which enables their direct incorporation into mortar formulations. The material was produced via chemical vapor deposition and characterized by scanning electron microscopy, thermogravimetric analysis, energy-dispersive spectroscopy, and Fourier-transform infrared spectroscopy. The resulting nanostructured active silica (NAS) exhibited high carbon content (80.7%) and a 1350% yield, confirming efficient nanotubular deposition. Residual oxygen (9.12%), Mg (0.75%), and Al (0.17%) indicated partial retention of catalytic species, while Fe–Co promoters with Mg–Al modifiers enabled a catalytically active surface favorable to CNT growth. Mortars incorporating NAS restored the flexural strength losses associated with cement replacement by silica, achieving values comparable to the reference mixture and outperforming the silica-only sample; compressive strength increased by ~16.5%. These results demonstrate that NAS promotes effective CNT dispersion at the composite scale without additional dispersion techniques, reduces process complexity, and adds value to commercial silica, providing a scalable route for developing nanostructured cementitious composites for construction applications.