Modeling interlayer interfaces in 3D-printed concrete using a coupled cohesive contact approach

3D-printed concrete exhibits pronounced anisotropy as a result of its layered deposition process and the presence of interfacial contact zones, which significantly influence its mechanical response. This work presents a Finite Element framework enhanced with contact mechanics to explicitly model the interaction between adjacent printed layers. A cohesive contact formulation is adopted to describe the evolution of normal and tangential stresses at the interfaces. The model incorporates coupled normal and tangential traction–separation laws, enabling the representation of elastic, inelastic, and residual interfacial behavior. The elasto-plastic evolution of the interface response is governed by a quadratic failure criterion, with hardening/softening functions calibrated from direct tensile and shear tests. The numerical implementation relies on a classical return-mapping algorithm to ensure a consistent update of interfacial stresses and inelastic displacement components. The proposed model is validated against experimental data for three different materials through case studies involving direct tension, shear, compression, and four-point bending tests. The results demonstrate that the cohesive contact formulation accurately captures the role of interfacial properties in governing macroscopic strength, failure mechanisms, and anisotropic behavior. Specifically, the proposed model is capable of reproducing post-peak softening through calibrated hardening/softening laws. Experimental validation of this constitutive behavior is provided for the case studies with complete force–CMOD measurements, whereas the remaining cases validate primarily the peak response and the associated failure mechanisms.