The effects of nano-Ti O2(NT) on the multiscale pore system and morphology of cement mortars were studied by X-ray computed tomography (X-CT), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) method. The obtained results from X-CT showed that microscale pores (from 20 μm to 200 μm) of mortars mixed with 2.5 wt% NT were significantly refined. When the content of NT is more than 2.5 wt%, the total pore volume and the number of pores begin to increase. However, when the amount of NT exceeds the optimal value, e.g., (2.5 < NT < 5%), the recorded 2D porosity (void area fraction), are still lower than the reference sample. Meanwhile, the microscopy results proved that, by adding 2.5 wt% NT, the pores of cement mortars were best filled, resulting in a more homogenous morphology. At the nanoscale, the BET results revealed a clear trend of increasing surface area and pore volume of the NT cement mortars, over the entire range of NT percentages, i.e., from 0 wt% to 10 wt%. This could stem from the formation of nanosized needle-shaped products in the presence of the nanoparticles. Further, the permeability of NT cement mortars was measured using a high-pressure core holder and the results showed that 2.5 wt% NT inclusions could reduce the permeability of the cement mortars by 32%. However, adding more NT (>2.5 wt.%) led to higher permeability. This is in line with the microscale pore analysis from X-CT. It can be concluded that adding a certain amount of NT (around 2.5 wt%) can modify the pore structure of cement mortars by changing the harmful microscale pores (permeability related) to the nano-sized benign pores, leading to a much stronger durability of cement-based materials.
- Brunauer-Emmett-Teller (BET)
- nano titanium dioxide (NT)
- scanning electron microscopy (SEM)
- X-ray computed tomography (X-CT)