Seebeck effect in carbon-nanotube-reinforced cement pastes

This paper presents a preliminary study on the thermoelectric Seebeck effect – generating electrical energy from a thermal gradient across a material, for example on a sun-exposed concrete slab – of a carbon nanotube-Portland cement nanocomposite. Such a thermoelectrically-active material could be used as a potential source of supplementary renewable energy. The addition of carbon nanotubes (CNTs) and nanofibres (CNFs) into Portland cement as nano-reinforcement have demonstrated in numerous previous studies to impart significant enhancements to the mechanical performance and electrical conductivity of the resulting cementitious nanocomposite. However, to-date, there has been only limited investigation into the thermoelectric effect in this material. In this preliminary study, three cement pastes (0.3 water-to-binder) incorporating 5 % (by cement mass) liquid admixtures of dispersed CNTs, CNFs or no admixture (reference), were cast into 50mm cubes with copper mesh electrodes embedded within opposite specimen faces, cured in lime-saturated water for 7 days, then dried at 60 °C for 24 hours and allowed to cool to room-temperature prior to testing. Thermal gradients up to 40 °C were applied and maintained for 5 minutes across parallel faces of specimens, using a brass block heater and Peltier cooler set to 20.0 °C, after which time voltages across the specimens were recorded using a digital multimeter (accuracy ± 0.3 %). Preliminary results indicate that there is a strong Seebeck relationship for the 7-day-old nanocomposites investigated, with calculated Seebeck coefficients of approximately 0.7 – 1.0 mV/K. However, further investigation is required to elucidate the mechanism and possible convoluting effects, including capacitance, thermal conductivity, and the influence of CNT/CNF dose.