Effect of the curing process on the thermomechanical properties of calcium aluminate cement paste under thermal cycling at high temperatures for thermal energy storage applications

Abstract

Future perspectives to improve the energy efficiency of concentrating solar power (CSP) plants are focused on increasing temperatures above 600 °C. Among the different components of a CSP plant, the thermal energy storage (TES) medium must withstand high operating temperatures. Concrete was identified as an exciting candidate for its mechanical and thermal properties, needing further experimental research about this specific application. A fundamental concrete element is the cement binder, bringing cohesion to the composite components. As a requisite, the cement needs to be heat-resistant, and calcium aluminate cement (CAC) suits this demand. This cement is characterised by curing temperature-driven crystallisation changes, triggering an alteration of material properties. Considering that at 60 °C, the metastable hexagonal crystallisation is converted into a stable cubic crystallisation, seven curing cases were proposed in this study. After the curing process, thermo-mechanical properties of calcium aluminate cement paste were tested before and after thermal cycles from 290 °C to 650 °C. The results showed that, despite thermal cycling, the immediate hydration at 60 °C results in a higher thermal conductivity and compressive strength than standard curing at 20 °C.