Polyamide 12 as a mid-temperature phase change material in low-CO2 cementitious systems for thermal energy storage

This study presents an innovative approach for medium-temperature thermal energy storage (TES) by integrating low-CO 2 binders with a polymer-based phase change material (PCM), polyamide 12 (PA12). With a melting peak around 180 °C, PA12 is well suited for the most demanded industrial range (30–250 °C), addressing a key research gap in PCM applications above 100 °C. In addition to providing combined sensible–latent heat storage, PA12 improves the microstructure of cementitious matrices by enhancing pore connectivity and facilitating stress redistribution. Industrial decarbonization and the growing reliance on renewable energy require efficient TES materials capable of managing energy intermittency and recovering waste heat. Although concrete blocks offer an attractive TES solution, conventional Portland cement (PC)-based systems suffer from high CO 2 emissions. Consequently, this work explores low-CO 2 alternatives, alkali-activated (AAM), hybrid (HM) and LC 3 mortars. An experimental setup was designed to evaluate the thermal efficiency of mortars through controlled thermal cycling. Results show that low-CO 2 systems outperform PC. PA12 incorporation increased energy storage capacity by up to 18% in AAM mortars. LC 3 composites demonstrated improved thermal stability and controlled heat release. Furthermore, life cycle assessment (LCA) verify that alternative cementitious materials provide significant environmental benefits compared to conventional PC mortars, with AAM and HM systems showing the greatest reductions in CO 2 emissions and LC 3 systems achieving reductions above 30%. These findings highlight the potential of polymeric PCMs and alternative binders, offering a sustainable pathway to next-generation cementitious TES materials. • PA12 (nylon) integrated as PCM in AAM, HM, and LC 3 low-CO 2 mortars for TES. • AAM mortars retained >40 % higher strength than PC after thermal cycling. • Nylon increased energy storage capacity by up to 18 %. • AAM-PA12 showed highest energy density and fastest discharge in rapid TES cycles. • PA12 forms interconnected thermal channels that facilitate stress distribution.