Mechanical performance and life-cycle carbon reduction benefits of 3D-printed permanent-formwork columns filled with low-magnesia concrete

To improve the industrialization and low-carbon potential of reinforced concrete construction, this study proposes a short-column system consisting of a 3D-printed concrete shell as permanent formwork and a cast-in-place lean-magnesia-ore aggregate concrete infill. Axial compression tests were conducted on six shell–infilled short columns together with companion cast-in-place columns, with damage evolution monitored by acoustic emission (AE) and digital image correlation (DIC). A three-dimensional mesoscale finite element model was developed to account for pore-induced heterogeneity and interlayer weakening, and was used to interpret the observed failure process.Results show that the 3D-printed shell provides effective confinement and improves the axial capacity of the composite columns; the strength enhancement ranges from approximately 3.6% to 22.7% depending on cross-sectional shape and size, and circular specimens exhibit higher strength and a smoother post-peak response than square ones under comparable conditions. AE–DIC observations indicate progressive damage characterized by distributed cracking; tensile-type AE events dominate, while a limited fraction of shear-like/high-RA events may be associated with interfacial friction and local crushing effects. The mesoscale model satisfactorily reproduces the measured load–displacement response and crack evolution trends, supporting its use for mechanism interpretation. A cradle-to-gate life-cycle assessment suggests that the proposed system can substantially shorten construction time and reduce direct cost for the typical member considered, whereas the difference in embodied carbon is modest (~2.3%) and scenario-dependent under the adopted boundary and assumptions. Overall, the study provides experimental evidence and modeling support for 3D-printed permanent-formwork columns toward faster and potentially lower-impact construction.