Manufacturing and performance of eco-efficient cementitious storage tanks incorporating recycled demolition waste for thermal energy storage

Sustainable thermal energy storage (TES) is critical for industrial heat management, where more than half of energy demand occurs at temperatures below 250 °C. To bridge the gap between material design and practical application, this study conducted an initial laboratory-scale cyclic evaluation of eco-efficient single-tank TES prototypes. The key novelty of this work lies in the holistic validation of systems in which the cementitious tank wall serves not only as the primary structural component but also as an active sensible heat storage medium. To this end, the thermal performance of three TES tanks manufactured with Portland cement (PC), alkali-activated slag (SLAG), and hybrid slag (HSLAG) mortars was comparatively assessed under cyclic operating conditions. In addition, construction and demolition waste (CDW) was incorporated as a low-cost recycled filler, representing specifically 20 wt% of the TES system, and compared with volcanic rock (VR) as a conventional benchmark. The experimental validation involved five repeated air-based charge–discharge cycles between 30 °C and 180 °C to assess thermal stability, energy storage, and discharge performance. After these cycles, all tanks exhibited initial thermal stabilization. SLAG and HSLAG systems reached slightly higher temperatures in the lower tank region and showed faster stabilization with reduced mass loss compared to PC. With larger thermal gradients, alternative binders delivered discharge energies comparable to the PC reference, with differences of approximately 2 kJ/kg. While VR enhanced internal heat transfer, tanks filled with CDW released similar amounts of energy during discharge. The successful operation of these prototypes provides empirical proof of concept, demonstrating the technical feasibility of combining low-CO 2 cementitious binders with recycled demolition waste in TES tanks, offering a cost-effective and environmentally favorable alternative to conventional designs.