Feasibility of 3D Printing on Environmentally Friendly Cementless Materials with Low Thermal Conductivity

This study investigates ultra-fine fly ash (UFA) and co-fired fly ash (CFA) to produce binary cementless binders without alkali activators and determines the effects of molding temperatures (17 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, and 90 ℃) on thermal conductivity and microstructures. The pastes are subjected to flow and expansion tests to verify the mixing state of the two industrial by-products for a fixed water-to-binder ratio of 0.4. Compressive strength, water absorption, density, thermal conductivity, and scanning electron microscope analyses determine material properties and the optimal molding temperature. Results reveal that higher hardening temperatures lead to higher water absorption and lower density. The 50 ℃ specimen exhibits the lowest thermal conductivity of 0.1796 W/m·K at 56 days. The printed specimens with UFA and CFA at a 1:1 ratio achieve a 28-day compressive strength of 9 MPa and a thermal conductivity of 0.2064 W/m·K.