Microstructure-Based Discrete Lattice Modeling of Interlayer Fracture in 3D-Printed Concrete

Extrusion-based 3D-printed concrete (3DPC) is characterized by pronounced anisotropy and reduced interlayer strength due to its layer-wise manufacturing process. Recent experimental work indicates that the interlayer forms a mechanically distinct filament interfacial zone with altered particle content, local stiffness, and incomplete bonding at filament boundaries. A numerical framework must therefore account for the microstructural heterogeneity induced by printing in order to predict interlayer failure realistically. This contribution presents a microstructure-based discrete lattice model for fracture in 3DPC. The material is represented by a regular three-dimensional X-braced truss lattice in which the cementitious matrix and aggregates are resolved explicitly. The printed interlayer is modeled as a core–filament-interfacial-zone–core arrangement with spatially varying particle volume fraction, particle size, and local stiffness. Damage and fracture are described at the bond level, allowing crack initiation, localization, and propagation to emerge naturally from the underlying heterogeneity. To capture the brittle softening response, the equilibrium problem is solved using a dissipative arc-length solver. The main objective of the study is to identify which interlayer parameters most strongly influence tensile strength and fracture behavior. The effect of particle distribution across the filament interfacial zone is examined, including smooth profile variations motivated by experimental observations of particle depletion in the interlayer region. Additional parameters include the thickness of the interfacial zone, particle-size contrast between the filament core and interlayer, and reduced stiffness of the interfacial zone. The resulting simulations are used to compare crack paths, load–displacement response, and localization patterns for different microstructural scenarios. The proposed framework links experimentally observed interlayer morphology to the meso­scale fracture response of 3DPC. At the same time, it serves as a basis for future multiscale extensions using the QuasiContinuum methodology, enabling efficient simulation of larger printed structures while retaining explicit microstructural resolution in critical regions.