The effect of ZnO nanoparticles on thermoelectric behavior and fresh properties of cement paste

Close to 60% of energy produced in the U.S. is wasted as heat, which can be directly converted into electricity using thermoelectric (TE) technology via the Seebeck effect. However, the potential use of TE technology for energy harvesting has not been fully explored yet, especially in civil infrastructure applications. Therefore, the aim of this work is to investigate the possibility of developing TE concrete by incorporating semiconductor nanoparticles, such as zinc oxides (ZnO) and ZnO alloys in cement paste. This study has systematically evaluated the influence of aluminum ZnO (AZO) nanoparticles and undoped zinc oxide (ZnO) nanoparticles on the thermoelectric, hydration, and rheological behavior of portland cement paste. In order to elucidate the thermoelectric efficiency of semiconductors nanoparticles in cement paste, physical and chemical experiments were performed on ordinary portland cement pastes with water to binder ratio of 0.35 dosed with 0, 0.2, 0.4, 0.6, 0.8, and 1% weight fraction of ZnO and AZO nanoparticles. At the SMART Lab at Purdue, the thermoelectric behavior was evaluated with a newly developed test method of Seebeck coefficient measurement on cementitous materials, along with electrical and thermal conductivity measurements. In order to elucidate the chemical aspects of the hydration properties, X-ray diffractometry, differential scanning calorimetry, thermogravimetric analysis, and fourier-transform infrared spectrometry were performed on the samples. The effect of aluminum doped zinc oxide (AZO) and undoped zinc oxide (ZnO) nanoparticles added to the superplasticizer adsorption isotherm and rheological properties of cement paste composites were evaluated and the adsorption isotherm and zeta potential of pastes containing different proportions of ZnO and AZO nanoparticles were analyzed. The mechanism of superplasticizer adsorption by nanoparticles was found to be a dominant factor that controlled the rheological properties of composites. The mixtures containing 0.4 wt. % cement paste AZO nanoparticles showed excellent workability retention as compared to the reference sample, while, the poor workability retention was observed at higher dosages. The pastes containing AZO exhibited a preferred hydration behavior. Results also indicated that both ZnO and AZO nanoparticles can improve the thermoelectric properties of cement paste, and the highest thermoelectric properties of composites was found with 0.4% weight fraction of nanoparticles. The addition of 0.4 wt. % cement paste AZO nanoparticles resulted in 17% increase in Seebeck coefficient, 9% decrease in thermal conductivity, and 37% increase in electrical conductivity compared to that of reference specimen. This suggests that AZO can be potentially used for thermoelectric energy harvesting purposes to use the temperature difference between the ambient and the pavement layers, without compromising hydration and rheology behavior of cement composites