Yield stress and thixotropy control of 3D-printed calcium sulfoaluminate cement composites with metakaolin related to structural build-up

The three-dimensional (3D) structural build-up with the precision has proposed new requirements related to yield stress and thixotropy in the 3D-printed cementitious materials. In this study, the static and dynamic yielding behaviours of 3D-printed calcium sulfoaluminate (CSA) cement composites with metakaolin were studied to understand the relationship between thixotropy and structural build-up through the powder-based extrusion system. Experimental results show that the static yield stress implemented by the constant shear-rate-controlled protocol in the 3D-printed CSA cement paste increased significantly with rest time. Dynamic rheological behaviours were investigated by the Bingham and Herschel-Bulkley model. Given the change of flocculation structure and shear-thinning behaviour during the shear period, Herschel-Bulkley model is more suitable for studying the dynamic rheological properties of 3D-printed CSA cement paste. Moreover, the thixotropy can be well improved by the addition of metakaolin, and the correlation between the structure deformation and thixotropy of 3D-printed CSA cement paste further proved that the improved thixotropy is beneficial to 3D-printed structural build-up. In conclusion, developing a 3D-printed CSA cement composites with the controllable yield stress and thixotropy is significant for structural build-up in the 3D-printed construction materials.