Abstract
This study developed and verified a novel, alkali-free cementless material for 3D printing, formulated entirely from industrial by-products: circulating fluidized bed co-fired fly ash (CFA), blast furnace slag, fly ash, and reactive ultra-fine fly ash (RUFA). The research aimed to eliminate cement and hazardous liquid alkali activators by using the self-activated properties of CFA to activate the slag. The experimental program evaluated rheological properties for printability, compared the compressive strength of cast and 3D-printed specimens to assess anisotropy, and analyzed thermal conductivity and interlayer bonding using optical microscopy. Results showed the optimized cementless mixtures achieved stable fluidity and good extrudability, though with longer setting times than traditional alkali-activated materials (AAMs). While AAMs had superior compressive strength (over 60 MPa), their rapid hardening created weak interlayer bonding. Conversely, the cementless composites maintained continuous fusion and achieved lower thermal conductivity (minimum, 0.233 W/m K) due to an interstitial pore structure from RUFA. The study concluded that while AAMs were better suited for high-strength applications, the developed alkali-free composite offered a sustainable and energy-efficient solution for non-structural elements, striking a balance between buildability and thermal insulation. Its innovation lay in creating a self-activating, all-waste binder system that avoided corrosive chemicals while enabling tunable thermal properties in additive manufacturing.