Finite-Element Modeling Framework for Mechanical Response of 3D-Printed Concrete: Elucidating Directional, Interface, and Fiber Effects

The mechanical behavior of three-dimensional (3D)-printed concrete is a complex interplay of the concrete’s intrinsic properties (rheology and mechanics), and printing parameters (speed and layer dimensions), and the latter directly affects the number and quality of interfaces and filaments. Whereas experimentally identifying optimal combinations of print and interface parameters is challenging and time-consuming, numerical modeling offers an efficient alternative. This study presents a coupled experimental–finite-element (FE) modeling approach to study the impact of filament and interface properties on the mechanical behavior of 3D-printed concrete elements. An orthotropic viscoelastic-viscoplastic material model is used to model the extrudate filaments, whereas the interfaces are modeled using a traction–separation law–based cohesive material model. Three validation tests were modeled: (1) compression tests involving 3D-printed cubes, (2) four-point bending test using plain 3D-printed beams, and (3) four-point bending test using fiber-reinforced 3D-printed beams. The compression test was modeled with interlayer joints (ILJs) and interfilament joints (IFJs) treated as distinct entities. The compression models not only accurately capture the printed elements’ direction-dependent compression response, but indicate that failure initiated at the interfaces, similar to what was observed in the experiments. The inclusion or exclusion of ILJ and IFJ interfaces resulted in similar outcomes for the four-point bending test of beams without fibers. Thus, for fiber-reinforced beams exhibiting orthotropic behavior, the pronounced strain-softening behavior was modeled by omitting the ILJ and IFJ interfaces. The strengths predicted by the model were within 10%–20% of the experimental average strengths, demonstrating the FE model’s effectiveness in replicating the mechanical behavior of 3D-printed concrete. The developed framework can be used to optimize the print parameters, paving the way for enhanced product quality and mechanical performance.