Time-dependent interfacial pore evolution and anisotropic compressive response in 3D-printed one-part geopolymer concrete: experimental characterization and mechanism modeling

This study investigates the impact of printing intervals on the anisotropic performance and interfacial pore morphology of one-part 3D-printed geopolymer concrete. A multiscale framework integrating mechanical tests, X-ray CT, and finite element analysis (FEA) was established. Results indicate that extended intervals (up to 3.0 h) exacerbate strength degradation and anisotropy. Notably, 3D porosity increased by 13.6% and 47.2% as the interval reached 0.5 h and 1.0 h, respectively. This was accompanied by a transition from spherical to ellipsoidal pores preferentially aligned along the print direction. A theoretical model was developed to quantify pore deformation based on lateral extrusion stress and material properties, successfully predicting pore eccentricity evolution. FEA simulations further revealed that stress concentrations and failure modes are governed by the orientation of these deformed pores relative to the loading direction. This work establishes a critical link between interval-induced pore architecture and mechanical integrity, suggesting that a printing interval below 0.5 h is essential to suppress pore elongation and ensure reliable interfacial bonding in printed geopolymers.