From fabrication process to structural performance: exploring test procedures and design models for digitally fabricated concrete

Abstract

Digital fabrication enables new possibilities for structurally optimized and resource-efficient reinforced concrete construction. In particular, extrusion-based 3D concrete printing (3DCP) allows the production of load-adapted geometries without conventional formwork. However, the structural application of reinforced 3D-printed concrete remains limited due to unresolved challenges regarding reinforcement integration and the applicability of existing structural design approaches. This paper presents a multimodal fabrication strategy combining 3DCP, casting, and integrated carbon-fiber reinforced polymer (CFRP) reinforcement for the digital production of reinforced concrete members. To investigate the resulting structural behavior, a comprehensive experimental program was conducted covering material characterization, bond behavior, bending, shear, and punching shear. Particular focus was placed on the interaction between fabrication-induced characteristics and structural load-transfer mechanisms. The experimental investigations demonstrate that optimized nozzle orientation significantly improves the bond behavior between CFRP reinforcement and 3D-printed concrete. Compared to cast reference specimens, the bond capacity of the printed specimens was reduced by 23–41%, depending on the nozzle orientation. Structural tests on beams revealed that conventional sectional analysis approaches can successfully predict flexural behavior. In contrast, the experimentally observed shear resistance of the beam without shear reinforcement was approximately 48% lower than the guideline-based prediction, highlighting the necessity of considering fabrication-induced anisotropy and interlayer delamination. The observed discrepancies are attributed to the anisotropic material behavior and reduced interlayer bond resulting from the layer-wise fabrication process. To address these effects, an existing physics-based shear model was critically evaluated and extended for application to digitally fabricated concrete members. In particular, the Shear Crack Propagation Theory (SCPT) was extended by incorporating interface delamination mechanisms specific to 3D-printed concrete. In combination with experimentally derived reinforcement contributions, the proposed hybrid modeling approach reproduced the experimentally observed shear capacities with deviations below 9%. The proposed framework demonstrates that reliable structural design of reinforced 3D-printed concrete cannot rely solely on conventional empirical approaches but requires mechanics-based models explicitly accounting for fabrication-induced characteristics. The presented methodology provides a transferable framework linking digital fabrication processes with structural performance and establishes a basis for the development of future design provisions for reinforced 3D-printed concrete.