Effect of TiO2 Nanoparticles on the Fresh Performance of 3D-Printed Cementitious Materials

3D printing (3DP) of cementitious materials shows several advantages compared to conventional construction methods, but it requires specific fresh-state properties. Nanomaterials have been used in cement-based materials to achieve specific fresh and hardened properties, being potential candidates for 3DP applications. However, there are no reports on using TiO₂ nanoparticles (nano-TiO₂) in 3DP cementitious composites. Thus, the current work aims to assess the effect of nano-TiO₂ on the fresh performance of 3DP cementitious materials. For this purpose, nano-TiO₂ was incorporated in pastes and mortars from 0 to 1.5 wt.%. Time-resolved hydration (in situ XRD) and rheological and printing-related properties (buildability and printability) were evaluated. Results showed that nano-TiO₂ particles enhanced the cement hydration kinetics, leading to further ettringite formation up to 140 min compared to plain cement paste. Rheological measurements showed that the nano-TiO₂ incorporation progressively increased the static and dynamic stress, viscosity, and structuration rate of pastes. Furthermore, nano-TiO₂ improved the buildability of the composites, progressively increasing the maximum number of successive layers printed before failure from 11 (0 wt.% TiO₂) to 64 (1.5 wt.% TiO₂). By contrast, the nano-TiO₂ addition reduced the printability (i.e., the printable period during which the sample was able to be molded by the 3D-printing process) from 140 min (0% TiO₂) to 90 min (1.5% TiO₂). Thus, incorporating “high” nano-TiO₂ contents (e.g., >1 wt.%) was beneficial for buildability but would require a quicker 3DP process. The adoption of nano-TiO₂ contents of around 0.75–1.00% may be an interesting choice since it reduced the printability of paste by 30 min compared with the control mix but allowed for printing 24 layers (118% higher than plain mortar).