Evaluating thermal storage capability of recycled construction materials: an experimental approach

Materials for Renewable and Sustainable Energy https://doi.org/10.1007/s40243-025-00299-6 (2025) 14:25 ORIGINAL PAPER Evaluating thermal storage capability of recycled construction materials: an experimental approach Fardin Jafari1 · Giovanni Semprini2 · Alessandra Bonoli1 Received: 30 September 2024 / Accepted: 11 February 2025 © The Author(s) 2025 Abstract Granular materials like sand have gained importance in thermal storage applications due to their stability and cost-effectiveness. However, excessive usage of sand can pose environmental issues. This study investigates recycled construction materials such as glass, asphalt, ceramic, and concrete as alternatives to natural sand for low-temperature TES applications. The materials were processed to similar grain sizes and evaluated for their chemical, thermophysical, and thermal storage properties through a six-hour charging cycle at 60 °C. XRF analysis revealed significant compositions, including high oxygen and silicon content in concrete and sand, respectively. Results indicate that sand with 0.189 W/m K recorded the highest thermal conductivity compared with concrete 0.172 W/m K, glass 0.131 W/m K, ceramic 0.159 W/m K and asphalt 0.159 W/m K. A higher specific heat capacity was observed in concrete at 755 J/kg K, followed by asphalt at 732 J/kg K, glass at 708 J/kg K, and sand at 688 J/kg K. However, ceramic is categorized for a lower specific heat capacity of 682 J/kg K. Absolute density evaluation indicates that sand is the densest material with 2662 kg/m3, contrary to concrete 2480 kg/m3, glass 2421 kg/m3, ceramic 2285 kg/m3, and asphalt 2436 kg/m3. More to the point, the Ragone plot for specific power and energy highlighted that ceramic has a rapid energy release and concrete demonstrated sustained energy storage capabilities. Volumetric power and energy density assessments indicated sand's outstanding performance. However, concrete registered a superior thermal storage among recycled materials. The results highlight that recycled materials, specifically concrete can be used for thermal storage applications like water heating in poor communities. Keywords Thermal storage · Recycled materials · Ragone plot · Thermal conductivity · Specific heat capacity Introduction Thermal energy storage has increasingly gained importance in modern energy management and has become a key factor in conserving renewable energy, like solar or wind [1–3]. One of the major challenges in the building and residential sectors is reaching nZEB or ZEB targets, where energy needs, especially those for heating and domestic hot water, must be completely supplied by renewable sources. Due to the different time profiles of users' energy consumption and energy production from * Fardin Jafari 1 Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, Bologna, Italy 2 Department of Industrial Engineering, University of Bologna, Bologna, Italy renewable sources, it is necessary to provide energy storage. Therefore, the produced energy can properly be stored and supplied to the building technical systems at the requested time [4–6]. Using lithium-ion batteries to store electricity from renewable sources imposes significant costs for their provision and maintenance, and they also have a short lifespan so thermal energy storage can be a suitable option instead of batteries [7–9]. Instead, the thermal energy can be stored in more sustainable and cheaper systems through various materials and in different physical states, like solid, molten, and liquid phases [10, 11]. TES performance relies heavily on key thermal properties of materials, such as thermal conductivity and specific heat capacity, which determine their efficiency in storing and releasing energy. Materials with higher thermal conductivity facilitate efficient heat transfer, while those with higher specific heat capacity store larger quantities of energy. Thermal oils and liquid sodium are liquid TES materials often used for storage and heat exchanger fluid because Vol.:(0123456789) 25 Page 2 of 13 they have high thermal conductivity [12, 13]. Materials like molten salts and metals are considered thermal storage materials for solar energy concentration. However, keeping molten materials at a constant temperature is crucial to their application to achieve optimum efficiency since overheating can reduce their efficiency[14–16]. Meanwhile, molten state TES can damage the storage vessel and piping networks due to solidification[17]. Metals can also cause corrosion inside the storage tank, so specific materials are required and associated additional costs [18]. One of the TES materials of interest in solid-state is sand, which offers higher thermal tolerance with a melting point of 1700 °C [19, 20]. Additionally, sand provides notable cycle stability over time, making it a reliable material to store thermal energy [21–23]. Therefore, sand has gained considerable attention in designing thermal storage systems. Various studies have been developed to optimize sand performance in thermal storage systems by altering grain size, coating, or compounding with other materials. Xu et al. [19] evaluated the sand size to gain the optimum thermal storage. Then, they employed numerical and experimental investigation to increase the heat transfer inside their samples by adding Xceltherm (synthetic oil) and Hitec (inorganic salts). They exhibited that the grain size between 0.6 and 1.7 mm with a porosity of 0.38 is the suitable size distribution. They also found that if Hitec-saturated sand is utilized for storage media, energy can be stored more than Xceltherm, almost 35%. The findings show that new approaches developed under sensible heat storage can be significant in solar energy storage applications. García-Plaza et al. [24] prepared some sand coating utilizing a top-concentrated irradiation lamp in fluidized bed conditions. They found that graphite and carbon coats enhance the raw sand energy absorption between 30 and 40% due to higher thermal absorptivity. While the coats demonstrated constant properties after ten charging and discharging cycles, the color of graphite-coated sand faded from dark black to grey. Sand is also used to mix with PCM materials. Barbi et al. [25] mixed N-octadence and commercial PCM (RT28) with sand in a ratio of 30% v/v separately to analyze their distribution in latent heat thermal energy storage for shallow geothermal applications. The results indicate that the heat transfer accelerated in both mixtures, halving the phase change time. In addition, sand addition led to a limited supercooling up to 1 °C in N-octadence. However, the phenomenon was absent in commercial PCM. In a related paper, Liu et al. [26] conducted some investigations into the thermal properties of recycled rubber-sand mixture via thermal needle tests. The study examined the impacts of various factors on thermal conductivity, including moisture proportion, m (...truncated)