Numerically optimised filament surface topology towards maximum bond strength in 3D printed concrete

3D printed concrete (3DPC) is emerging as a high-impact construction automation technology, with numerous structures completed globally. A major challenge is anisotropic mechanical behaviour caused by weak bonding between concrete filaments, also prevalent in other additive manufacturing forms. Literature shows inadequate bonding reduces tensile strength by 45.6 %, resulting in filament delamination rather than bulk fracture. This study presents a comprehensive investigation into optimising filament surface topology to maximise interlayer bond strength in 3DPC. Using advanced numerical simulation frameworks and experimental methodologies, various interlayer topologies for filaments with 40 mm× 20 mm (w x h) cross-sections were explored, including different tongue-and-groove depths, widths, and counts, as well as stress concentration effects. An interface-based finite element model in DIANA was validated with experimental results. A single 5 mm groove increased tensile bond strength by 42.9 %, with no significant improvements beyond this depth. Groove width optimisation achieved a peak improvement of 98.21 % at 20 mm width. Introducing three 7 mm deep grooves yielded a 124 % strength increase. Incorporating fillets at tongue-and-groove corners reduced stress concentrations, enhancing bond strength by 179.46 %. The tensile capacity of interlayers reached within 6.57 % of bulk tensile strength, indicating near-isotropic behaviour. Employing tongue-and-groove topologies using recycled 3D-printed plastic nozzles provides a cost-effective, safer, and environmentally sustainable approach, outperforming traditional chemical and thermal treatments. Finally, universal guidelines are provided for achieving maximum bond strength across varying filament dimensions.