PSI - Issue 67

Jorge S. Dolado et al. / Procedia Structural Integrity 67 (2025) 23–29 Jorge S. Dolado/ Structural Integrity Procedia 00 (2024) 000–000

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densities on the order of 10 -4 Wh/kg. While this energy density falls significantly below that of lithium batteries, which typically reach 10 2 Wh/kg, cementitious materials are often associated with large structures. Thus, any perceived deficit in quality can be more than compensated for by quantity. For instance, a typical battery (approximately 10 grams) accommodates 1 Wh of energy. The same energy capacity could be stored within a cube of cement paste akin to the one used in Meng and Chung's research, but with dimensions of 3 meters on each side. Although the earlier work demonstrated the concept's feasibility, its implementation was not optimized, facing two main challenges: low energy density and non-rechargeability. Subsequent research endeavors in the field have been numerous, but two particularly noteworthy studies, in my view, stand out: Firstly, the study by Chen et al. (2018) suggested substituting the Ordinary Portland Cement (OPC) matrix with the zeolitic matrix of alkali-activated cements. The structure of alkali-activated cement matrices inherently enhances ionic conductivity due to their higher water content and the transport-favoring zeolite cavities. Consequently, the achieved energy densities saw a significant improvement, reaching approximately 10 -1 Wh/kg. Secondly, the research by Zhang and Tang (2021) focused on enhancing the design of cementitious anodes and cathodes, enabling up to 6 cycles of charging and discharging with energy densities of around 10 -2 Wh/kg. Their approach involved cementitious composites based on OPC cements, where zinc inclusions (anode) and MnO 2 (cathode) were replaced by meshes of carbon fibers coated via electrodeposition with iron and nickel, respectively. 3. Thermal Energy Storage Unlike Ordinary Portland Cement (OPC) concretes, those based on geopolymers and hybrid cements are recognized for their ability to withstand significantly higher temperatures, as noted by Qu et al. (2020). Taking this into account, Rajhoo et al. (2022a) investigated the heat capacity and thermal diffusivity of a commercial hybrid cement, as detailed in Martauz et al. (2016). Encouraged by the favourable performance of geopolymer concrete at elevated temperatures, a proof of concept study was recently conducted to assess a Thermal Energy Storage (TES) module under realistic temperature charge and discharge cycles. For comprehensive information, readers are directed to Rahjoo et al. (2022b), while Figure 1 (a) illustrates the prototype employed. Essentially, the design comprised a concrete block with a steel pipe terminated with two flanges. This TES module was flanged onto predetermined air heater tubes, as depicted in Figure 1 (b). Subsequently, four cycles of charging and discharging were executed, with the inlet air temperature (Tinlet) ranging from 200°C to 650°C. The temperatures recorded by the three temperature probes of the TES module and the one for Tinlet are depicted in Figure 1 (c). Notably, the TES prototype endured high operating temperatures consistently exceeding 500°C, aligning well with the thermal requisites of second-generation Concentrated Solar Power (CSP) systems. This success paves the way for further design enhancements utilizing Finite Element Method (FEM) and Artificial Intelligence (AI) methodologies, as outlined by Rahjoo et al. (2023).

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Figure 1. (a) Design of the TES prototype modules. (b) Experimental set-up within the air thermal loop. (c) Temperatures of the Geopolymer based concrete TES module for T inlet between 250ºC and 650ºC.