Fracture Toughness, Compressive Strength and Fracture Surface Morphology of Cement Mortars Modified with Nano-SiO2

This study investigates the effect of nano-SiO₂ on the mechanical properties and fracture surface morphology of cement composites. The focus was on fracture toughness (<i>K_Ic^S</i>) and compressive strength. Composites with nano-SiO₂ showed up to 63% higher fracture toughness and 68% higher compressive strength than unmodified ones. The influence of nano-SiO₂ content (0.09-2.91% by binder mass) and water-to-binder ratio (0.43-0.57) was examined using a Central Composite Design. Properties improved with higher nano-SiO₂ content and lower <i>w/b</i> ratio. Fractographic analysis using laser profilometry revealed a clear correlation between the fractal dimension (<i>D</i>) of fracture surfaces and <i>K_Ic^S</i> and fcm. Lower <i>D</i> values indicated smoother fracture surfaces and denser microstructures. The results clearly show that changes in the composition-particularly the nano-SiO₂ content and the water-to-binder ratio-determine the development of the microstructure, which in turn governs the mechanical properties of the material. Consequently, the study establishes a coherent, quantitative relationship between mixture composition, fracture microstructure, and the macroscopic properties of the composite.