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)

Effect of the superplasticizer addition time on the fresh properties of 3D printed limestone calcined clay cement (LC3) concrete

Although 3D concrete printing (3DCP) is considered one of the most significant innovations in the construction sector, its large cement consumption remains an environmental concern. In response, limestone calcined clay cements (LC³) have emerged as a promising alternative to Portland cement (PC) due to their potential for reducing environmental impact. While previous studies have shown the influence of addition timing of superplasticizer (SP) on the fresh performance of PC, its impact on LC³, particularly in the context of 3DCP, remains less understood. This study assessed the effect of the SP addition time (either directly with the mixing water or with a 10-min delay) on the rheology and printing-related properties of LC³ and PC. Rotational rheometry and 3DP-related tests were conducted over two hours, besides hydration assessment through thermogravimetric analysis (TGA). The results showed that adding SP directly to LC³ led to significantly higher yield stress (1.2–2.5 times) and viscosity (14–59 % higher) values compared to delayed SP addition within the same time frame. However, LC³ exhibited slower rates of yield stress and viscosity increase over time in contrast to PC (with Athix structuration rate approximately 92 % lower for LC³). These tendencies influenced printability performance. While direct SP addition reduced PC's open time from 100 to 30 min, it had no impact on LC³ 's open time, which remained at 80 min. TGA analysis yielded additional insights, highlighting that hydrating LC³ samples required a greater free water content to achieve the same yield stress as PC and this difference was attributed to the presence of calcined clay. These findings make contributions to the technical and scientific communities by enhancing comprehension of LC³ cement fresh behavior and solidifying 3DCP as a disruptive construction method