Thermoelectric engineered cementitious composites with low thermal conductivity for efficiency improvement of buildings

Thermoelectric cement-based materials are getting noticed for their ability to convert heat into electricity and reduce surface temperatures. This study developed thermoelectric ultra-lightweight engineered cementitious composites (ULW-ECC) with low thermal conductivity (0.478 - 0.668 W/(mK)) and low density (1003 - 1157 kg/m3). Carbon fibre (CF) of varying lengths (1 - 20 mm) and concentrations (0, 0.5, and 1.0 vol%) were incorporated, and the mechanical, electrical conductivity and thermoelectric performance of the composite were thoroughly examined. Additionally, the impact of saturation and drying treatment on thermoelectric conversion efficiency was assessed. The results revealed that the inclusion of mineral admixtures and fly ash cenospheres within the composite could decrease the content of OH- ions in pore solution due to the pozzolanic effect. This phenomenon led to the creation of a high-performance p-type ionic thermoelectric effect, with a Seebeck coefficient of 3.14 mV/degrees C. Moreover, treatments involving saturation and drying were found to respectively enhance and diminish conversion efficiency. Incorporating CF into ULW-ECC generates an ionic-electronic thermoelectric effect through the collaborative interaction of metal cations and positive hole carriers from both the pore solution and CF, respectively. Thermoelectric conversion efficiency varied with CF length and dosage, with a peak improvement in the Seebeck coefficient reaching 5.9 mV/degrees C. However, a sharp decline occurred when a continuous conductive network was formed.