3D-printed functionally graded concrete plates: Concept and bending behavior

Three-dimensional concrete printing (3DCP), as an innovative technology, has become increasingly popular owing to advantages such as cost-effectiveness, labor-saving, free of formwork and materials-saving. Using the layer-by-layer construction technique enabled by 3DCP, functionally graded concretes with different ultimate tensile strain (UTS) capacities are proposed in this paper, leading to an optimum design of concrete plates. Three types of concrete, which are designed to have different UTS capacities, namely engineering cementitious composites (ECC), normal concrete (NC) and gepolymer concrete (GC), are developed. Six groups of 3D-printed functionally graded concrete plates are fabricated and tested under bending. The results revealed that the load-bearing capacity of FGC-3-2-1 was comparable to that of ECC plates, while FGC-1-2-3 exhibited the lowest load-bearing and deformation capacities. Increasing the number of ECC layers enhanced both the load-bearing and deformation capacities. Conversely, changing the number of GC and NC layers when the number of ECC layers remained constant resulted in similar performance. Additionally, using ECC as a reinforcing layer for 3D- printed concrete structures significantly improved their load-bearing and deformation capacities. These findings suggest that the proper design of functionally graded concrete can substantially reduce the CO2 of concrete plates without compromising their mechanical properties. Finally, a theoretical model based on bond-slip laws was proposed and validated against the test results, providing valuable insights for the design and optimization of 3D- printed concrete structures.