Thermoelectric cement-based composites containing carbon nanotubes (CNTs): Effects of water-to-cement ratio and CNT dosage

This study investigates the effects of the water-to-cement (w/c) ratio and carbon nanotube (CNT) dosage on the thermoelectric and mechanical properties of cement-based composites. Four different types of w/c ratio including 0.2, 0.3, 0.4, and 0.5 were employed with three different dosages of CNT, including 0.15, 0.3, and 0.5 vol% (≈0.39 wt%). Additionally, pristine CNT and nitrogen-doped CNT were adopted to fabricate p- and n-type thermoelectric cement-based composites, respectively. The Seebeck coefficient, electrical conductivity, compressive strength, and isothermal calorimetry were then measured and evaluated. The test results indicate that at a w/c ratio of 0.5, the use of CNTs enhances the compressive strength of cement paste by up to 65.9 %. The isothermal calorimetry measurement also confirmed the acceleration of the hydration reaction by the CNTs added to the cement paste. A w/c ratio of 0.3 with CNT dosages of 0.3 and 0.5 vol% was also found to be the most effective in improving the Seebeck coefficient. Additionally, the highest Seebeck coefficients for the p- and n-type thermoelectric cement-based composites are 743.0 and −428.3 µV/K, respectively. Considering that a CNT dosage of 0.3 vol% is most effective in enhancing the electrical conductivity, the best cement-based composites in terms of thermoelectric properties comprise a w/c ratio of 0.3 and a CNT dosage of 0.3 vol%.