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 (KIcS) 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 w/b ratio. Fractographic analysis using laser profilometry revealed a clear correlation between the fractal dimension (D) of fracture surfaces and KIcS and fcm. Lower D 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.