Magneto-Responsive Flow Behavior and Early-Age Microstructural Evolution of 3D Printing Lightweight Concrete with Fly Ash Cenospheres (2025-11)¶

This study develops a magneto-responsive lightweight concrete with fly ash cenospheres (FACs) and micron-sized Fe3O4 particles (MPs) to address the critical challenge of balancing extrudability and buildability in 3D concrete printing. By applying controlled magnetic fields synchronized with printing stages, the rheological properties are dynamically adjusted through magnetic particles reorganization. The integrated methodology combines time-dependent rheological tests (including flowability at 0–30 min, shape retention at 20–23 min, and penetration resistance at 30–60 min) with microscale characterization (i.e., XRD, SEM-EDS, and X-CT) and interparticle magnetic force calculation. The results demonstrate that horizontal magnetic field-driven particle rearrangement occurs without chemical phase changes, with the optimal performance at water-to-binder (w/b) ratio of 0.37 where concrete viscosity enables stable magnetic network formation. SEM-EDS and X-CT analyses confirm the alignment of magnetic particles parallel to horizontal magnetic field, correlating with directional strength influence. Additionally, SEM-EDS further reveals preferential MPs accumulation at FACs interfaces after applying long-term horizontal magnetic field for 24 h. Furthermore, this study establishes a fundamental framework for magnetically controllable lightweight concrete, enabling real-time rheology adjustment during 3D printing to achieve adaptive and mechanically robust structures through magnetic-directed microstructural technology. This method can extend the printable time window by leveraging the increasing flowability enhancement effect of MP and resolve the extrudability-buildability conflict by providing high flowability without magnetic field and structural stability under a horizontal magnetic field (achieving an 85.1 % deformation reduction during stacking).