Crack resistance and micropore structure in CNT-modified FSC: a fractal analysis

The crack resistance of carbon nanotube (CNT)-modified face slab concrete (FSC) is critically influenced by its micropore structure. This study employed mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and fractal theory to characterise the microstructure of FSC incorporating 0, 0.06, and 0.10 wt.% CNTs, while evaluating its mechanical and fracture properties at 3, 7, and 28 days. Results indicated that the optimal 0.06 wt.% CNTs dosage enhanced the 7-day compressive strength, elastic modulus, and fracture energy by 28.4%, 15.1%, and 35.8%, respectively, while reducing total porosity by 11.0% compared with the plain group. CNTs incorporation also decreased the initial and secondary sorptivity coefficients by 20.4% and 7.1%, signifying a less connected pore network. Fractal analysis of MIP data revealed that CNTs reduced the fractal dimension of macropores (>10 µm) by 2.2% but increased that of nanopores (<300 nm) by 0.9% at 7 days, indicating a refined macropore structure and a densified nanopore matrix. SEM observations confirmed that CNTs improved crack resistance through pore-filling, hydration promotion, and microcrack-bridging effects. This study quantitatively correlates the fractal characteristics of the pore structure with the crack resistance of CNT-modified FSC, offering theoretical support for enhancing FSC durability.