Ionic thermoelectric effects in CSA and OPC hardened cement pastes

The main purpose of this work is to demonstrate the potential of calcium sulfoaluminate (CSA) cement for thermoelectric energy storage applications. Cement paste samples made from ordinary Portland cement (OPC) and CSA cements were produced and the Seebeck effect was studied on hydrated samples and on samples dried in an oven at 70 degrees C. The temperatures of both sides of the samples were recorded as well as the thermal voltage. The hydration process of OPC and CSA cements was followed by thermogravimetry analyses, as well as X-ray diffraction analyses. We report the observation of a large thermal voltage in both OPC and CSA cement typical of an ionic thermoelectric effect. Further, we study the difference in the thermal voltage observed between dried and non-dried samples and comment on the thermoelectric hysteresis phenomenon observed in some ion conducting systems. We attribute the complex behavior observed in the increment V versus time and increment V versus increment T curves (hysteresis-like behavior) to a complex and challenging multi-ionic thermal diffusion and drift framework. Moreover, water loss may play a very important role as depicted by the difference between the results observed in non-dried and dried samples.