Effect of coarse aggregate size on the thermo-mechanical stability and thermo-physical properties of concrete for thermal energy storage (TES) applications

Concrete has gained considerable attention as a medium for sensible heat storage in concentrated solar power (CSP) plants, yet its performance at elevated temperatures is highly dependent on the nature of the aggregates. In this work, we focus on the influence of coarse aggregate gradation on the thermo-mechanical response of concretes intended for thermal energy storage (TES) applications. Two concretes mixtures were prepared with identical binder content, fine aggregates, and a water-to-cement ratio fixed at 0.33. The sole distinction lay in the size distribution of the coarse aggregates: 5–8 mm (C-G1) and 10–16 mm (C-G2). The materials were subjected to a comprehensive testing program to evaluate compressive strength, thermal expansion, volumetric heat capacity, thermal conductivity, and microstructural assessment, both before and after one hundred heating cooling cycles reaching 400 °C. Across the board, C-G1 showed superior performance. After durability test (100–400 °C), the crucial properties of C-G 1 have slightly increased as it achieved a density of 2.368 g/cm 3 , porosity reduced to 11.5 %, and compressive strength of 51.85 MPa. Its thermal performance was also enhanced, with a volumetric heat capacity of 2.552 MJ/m 3 .K and a conductivity of 1.60 W/m.K. Microstructural analysis revealed, a lower density of microcracks in C-G1 sample compared to C-G2, indicating improved resistance to thermal fatigue. These findings show that using smaller-sized coarse aggregates can greatly improve the strength, heat performance, and long-term durability of concrete in TES systems and other structures that face high temperatures. • Concrete performance under repeated thermal cycling up to 400 °C was investigated. • Effect of coarse aggregate size (5–8 mm vs. 10–16 mm) on thermo-mechanical behavior studied. • Finer aggregates improved density, strength, and reduced porosity and thermal strain. • Combined DSC, TGA, LFA, and DIL analyses revealed enhanced thermal stability in C-G1. • Findings validate optimal aggregate size for durable concrete in TES applications.