Mitigating the strength-accuracy trade-off in calcium aluminate cement-based selective cement activation 3D printing via powder-bed regulation of liquid penetration

초록

Selective cement activation (SCA) is constrained by a strength-accuracy trade-off because liquid penetration is sensitive to powder-bed structure. This study investigated how limestone powder (LS) particle size and replacement level regulate packing, millisecond-scale droplet infiltration, hydration, pore evolution, dimensional accuracy, and mechanical performance in a calcium aluminate cement (CAC)-based SCA system. Finer LS increased powder-bed density and delayed liquid entry; at 20% LS2 replacement, this regulation produced a shallower and more regular solidified penetration geometry. High-speed imaging showed rapid liquid uptake in the control, delayed yet continuous wetting and infiltration in LS2_CL20, and prolonged retention of a nearspherical droplet followed by abrupt spreading and absorption in LS2_CL25. Thus, 20% LS2 replacement limited excessive downward penetration while maintaining liquid entry, whereas 25% replacement excessively delayed infiltration and reduced boundary regularity. LS replacement reduced X- and Z-directional errors, although the Y-directional error increased along the roller-spreading direction. LS2_CL20 achieved a 28d compressive strength of 21.63 MPa, 83% higher than the control, while open porosity and water absorption decreased from 26.99% to 17.45% and 18.98% to 10.68%, respectively. X-ray microscopy revealed fewer connected interlayer defects and refined pore-size and pore-shape distributions. The improvement arose from sequential coupling between powder-bed densification and surface-mediated hydration, promoting heterogeneous nucleation, carbonate-involved hydrate formation, and pore refinement. Fine LS therefore mitigates the strength-accuracy trade-off by jointly regulating powder-bed packing and transient liquid transport, providing a mechanistic basis for high-performance SCA powders.

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