Investigation of the thermal properties of clay composites reinforced with bio-based and polymeric residue for structural application

This study investigates the thermal performance of clay-based composites produced from termite mound soil (TMS) reinforced with recycled polymer and biomass waste materials. Departing from conventional clay/polymer composites, where clay acts as a filler, this research adopts an inverse approach, utilizing polyethylene terephthalates (PETs) and sawdust residues as fillers within a clay matrix. Composites were fabricated via hydraulic pressing at varying reinforcement levels (2-10 wt.%) and fired at 1200 ℃. A comprehensive thermal evaluation was conducted, focusing on key parameters such as porosity, bulk density, specific heat capacity, thermal expansion, thermal conductivity, and thermal diffusivity. The results indicate that porosity increased significantly with reinforcement content, ranging from 19% to 43% for PET-clay composites and from 19% to 33% for sawdust-clay composites. Correspondingly, bulk density decreased from 2.35 g/cm³ to 1.39 g/cm³ (PET-clay) and from 2.35 g/cm³ to 1.04 g/cm³ (sawdust-clay). Specific heat capacity showed a progressive rise with reinforcement, enhancing the composites’ thermal energy storage potential. Thermal expansion increased from 3.3% to 7.5% in PET-clay and from 3.3% to 7.3% in sawdust-clay composites, while thermal conductivity declined from 0.39 to 0.27 W/mK (PET-clay) and from 0.39 to 0.29 W/mK (sawdust-clay). Thermal diffusivity also decreased from 2.55 × 10⁻⁷ m²/s to 1.88 × 10⁻⁷ m²/s (PET-clay) and 2.55 × 10⁻⁷ m²/s to 1.96 × 10⁻⁷ m²/s (sawdust-clay), demonstrating reduced heat transfer rates with reinforcement addition. These findings validate the suitability of PET- and sawdust-reinforced termite mound ceramics as sustainable thermal insulators for energy-efficient building applications, while simultaneously promoting circular use of post-consumer and agricultural waste.