3D printing-driven dynamic migration of lightweight microspheres in the printable mortars: Experiment and modelling

Lightweight aggregates are inevitably prone to segregate during concrete construction due to their extremely low mass, thus seriously deteriorating the quality of concrete. This study utilized 3D printing technology to improve the spatial redistribution of lightweight microsphere aggregate (fly ash cenospheres, FACs) for enhancing the printability of printable mortars. Experimental and numerical simulation methods were jointly employed to elucidate the mechanisms behind the spatial redistribution of FACs and the printability improvement mechanisms of mortars. Results indicated that the partial replacement of sand with FACs led to distinct effects on the rheology, attributed to the interplay between water absorption and ball-bearing effects characteristic of such spherical microporous particles. Regarding printability, the inclusion of spherical FACs resulted in an effective increase in the maximum number of printed layers. And the risk of segregation during the printing process was reduced, as confirmed by both Discrete Element Method (DEM) simulations and X-CT results, thereby improving the structural homogeneity of printed components. Moreover, the simulation results using the DEM revealed that the extrusion process could drive the FACs to migrate towards the core of the strips, which influenced the mechanical and durability properties of printed structures. X-ray CT analysis confirmed that the separation and floating behaviors of FACs were mitigated by the 3D printing process, further validating the improved homogeneity of FACs. This work provides valuable insights into the spatial distribution of FACs during the 3D printing process, which is pivotal for ensuring the quality and reliability of lightweight 3D printed structures. © 2025 Elsevier Ltd.