Open Access

3D concrete printing is a technology that promises to bring digitalization in the construction phase of E&C industry. It brings automation in the construction process by removing the need for formwork and providing a much better geometrical flexibility in terms of construction of complex structures. However, owing to the novelty of the technology, it brings an added complexity compared to traditional methods which needs to be studied. As many parameters are involved in the process, a detailed knowledge about the parameters and their influence on the mechanical behaviour of the object being printed is limited. Because of this, these parameters are commonly determined using a trial-and-error approach which can lead to unforeseen failure during the printing process. A systematic approach to determine the optimal set of parameters is required so that the mechanical behaviour of the (freshly) printed concrete can be controlled. This work is aimed towards achieving a better understanding of the various parameters involved in the 3DCP process and how they affect the mechanical behaviour of the object being printed using a modeling and simulation approach. Additionally, it seeks to develop optimization strategies and process control methods based on numerical models. A physics based numerical model is developed with the focus on capturing the correct material response using von-mises plasticity model with non-linear isotropic hardening. An objective stress rate is used to account for geometric non-linearity. Time dependent material parameters are used to replicate the aging effect of concrete. A density-based step by step layer activation approach is used for the structural model to mimic the layer-by-layer printing process. Both failure modes namely plastic collapse and elastic buckling are observed qualitatively. Model calibration and quantitative comparison with experimental results are planned for future work. Furthermore, development of optimization strategies and building a digital twin of the process using the developed model and sensor data from the printer are also planned.

3D concrete printing (3DCP) brings automation in construction, reduces material usage, increases design flexibility, and eliminates the need for formwork. However, it is a complex process involving various parameters that are often defined by trial and error. This can lead to unforeseen failures during the print, such as buckling or yielding. Computational modeling can be used in the design stage to predict and prevent failure, during printing for real-time process control, and afterwards to assess how variations during printing affect the final structure. The structural failure during the print is primarily governed by how concrete behaves at the material level, making the choice of constitutive model crucial. Plasticity models are commonly used to assess buildability, with the Mohr-Coulomb criterion being a widely used approach [1]. However, its suitability for modeling fresh concrete for 3DCP, under such loading conditions and varying material properties is still an open research question. Furthermore, experimental studies have shown that fresh concrete exhibits non-linear behavior before failure [2], which is usually not considered in structural simulations of 3DCP. This work investigates the influence of plasticity models on different structural failure modes observed in 3DCP, specifically elastic buckling and plastic collapse. The non-linear behavior of fresh concrete is accounted for by incorporating non-linear isotropic hardening into the plasticity models. A Von-Mises plasticity model and a Mohr-Coulomb model with a hyperbolic smooth approximation are implemented, both incorporating non-linear hardening. An objective stress rate formulation is adopted to consider geometric non-linearity for accurate buckling predictions. As freshly deposited layers structurate over time, an age-dependent model is implemented to capture the stiffness and strength evolution of printed layers. To simulate the layer-by-layer process, a pseudo-density-based activation method is used, allowing sequential activation of layers as printing progresses. Model parameters are identified for different ages using Bayesian inference via inverse finite element modeling by numerically replicating stress-strain data from uniaxial compression tests on samples at different ages. Printing simulations are conducted for thin-walled and cylindrical structures, demonstrating the influence of choice of plasticity model on buckling behavior and material failure.

Der 3D Betondruck ermöglicht die effiziente und ressourcenschonendere Herstellung maßgeschneiderter Betonstrukturen. Trotz des großen Potentials gibt es bisher keine einheitlichen Normen und Standards für den sicheren und robusten 3D Betondruck. Der Beitrag zeigt das Potential numerischer Methoden und Modelle zur effizienten und ressourcenschonenden Design- und Prozessoptimierung des 3D Betondrucks. Dazu werden die aktuellen Forschungsarbeiten im Bereich der Entwicklung robuster und zuverlässiger numerischer Zwillinge, geeigneter Optimierungstools sowie digitaler Workflows diskutiert.