Recycling construction wastes: thermo-physical characterization of composite mixtures based on chamotte, marble powder, and red clay

• Waste marble and chamotte improve thermal behavior of eco-efficient bricks. • Thermal conductivity decreases with more marble, enhancing insulation. • Chamotte increases conductivity and density, improving heat transfer stability. • Results support circular economy via sustainable brick waste valorization. This study investigates the thermophysical behavior of innovative powder mixtures composed of red clay, chamotte, and marble powder, with the aim of identifying formulations suitable for refractory plates capable of storing heat and improving energy efficiency in industrial furnaces. Unlike previous studies, which examined these materials individually, this work explores for the first time the combined use of the three components, offering an original approach to optimizing thermal performance through controlled microstructural adjustments. Thermal conductivity values of the mixtures ranged from 0.21 to 0.25 W/m.K, depending on the proportions of chamotte and marble powder. Specific heat capacity varied between 705 and 794 J/kg.K, while bulk density ranged from 1626 to 2014 kg/m³, revealing strong sensitivity to particle size and packing. Derived thermal diffusivity and effusivity values ranged from 1.09 × 10⁻ 8 to 8.77 × 10⁻ 9 m²/s and 512.5 to 599.3 J/m².K.s¹ / ², respectively, highlighting significant contrasts between insulating marble-rich mixtures and thermally responsive chamotte-rich formulations. These results demonstrate the potential of these ternary mixtures for the development of energy-efficient refractory components capable of retaining heat even after furnace shutdown. The study provides new insights into the valorization of industrial by-products and lays the groundwork for future investigations on fired samples and full thermomechanical characterization.