Development of Sustainable, Thermal-Insulated, and Load-Bearing Material and Modular Infill Wall Elements via 3D-Printed Formwork

Unlike flammable organic insulation, non-combustible inorganic materials offer superior fire safety despite higher thermal conductivity. Recent research focuses on developing innovative, sustainable inorganic solutions using natural and waste-based raw materials. Accordingly, in this study, a thermal insulation material (TIM) design is presented for sustainable buildings. Specifically, white cement, fine and powdered pumice, hydraulic lime were formulated using Response Surface Methodology (RSM) with a Box–Behnken approach. A total of 46 mixtures were produced and cured under ambient conditions for 28 days before undergoing mechanical and physical testing in the experimental phase. ANOVA-validated quadratic models show all mixtures have low densities below 1.2 g/cm3 and porosities of 35.52–39.62%. Optimal Run 23 achieves 11.55 MPa compressive strength, 2.53 MPa bending strength, and 0.25 W/m⋅K thermal conductivity. In addition, 3D-printed modular walls exhibit ductile behavior and maintain structural integrity up to 600 °C. Furthermore, a supplementary assessment of the optimal mixture modified with recycled concrete waste (Run-23+) demonstrated the viability of waste-aggregate integration for improved circular-economy performance. Microstructural analyses via XRD and SEM confirmed the dense formation of calcium silicate hydrate (C–S–H) networks and active pozzolanic reactions. Consequently, the present study demonstrates an advanced composite that combines low density with structural capacity, establishing a novel load-bearing thermal insulation material (LB-TIM). Moreover, by integrating this optimized LB-TIM mixture with custom designed 3D printed formwork technology, this study provides a novel and scalable manufacturing approach for sustainable, thermal-insulated and load-bearing material and modular infill wall elements.