Multiscale pore structure analysis of nano titanium dioxide cement mortar composite

Shafaei, Davood and Yang, Shangtong and Berlouis, Leonard and Minto, James (2020) Multiscale pore structure analysis of nano titanium dioxide cement mortar composite. Materials Today Communications, 22. 100779. ISSN 2353-4928

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    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.