Alkali-activated and hybrid materials: Alternative to Portland cement as a storage media for solar thermal energy

Abstract

This study is part of the research line that sees it necessary to develop materials that are alternatives for Portland cement (PC), using industrial by-products such as blast furnace slag and fly ash. This line arises because of the serious environmental consequences suffered by our planet throughout many decades, which have led the cement industry to reduce the amount of CO₂ emitted in the production of PC, since it is a highly polluting process. The chemical and physical properties of the materials were studied. In this way, the study of the thermal properties is interesting to test the feasibility of the mortars to use them as solid media to storage thermal energy, since most of the research focus on the thermal properties of concrete is oriented toward fire resistance. Storing solar thermal energy improves the operation of solar power thermal plants. It is being studied that the use of concrete (composed of PC) contributes efficiently to concentrated solar power (CSP) technology. To avoid the use of PC due to environmental concerns, alkaline-activated mortars are manufactured with blast furnace slag using alkaline solutions such as sodium hydroxide (NaOH) and commercial sodium silicate (SiO₂/Na₂O = 0.8), as well as hybrid mortars using 80% fly ash or blast furnace slag and 20% PC. After experimental analysis and a simulation to measure the conduction within the mortars through a commercial Computational Fluid Dynamic software (CFD, ANSYS Fluent), it can be concluded that the mechanical and thermal properties of most of the alternative mortars manufactured in this study are better than the ones obtained in the PC. Most notably, the slag alkaline-activated mortar increases those properties significantly.