Development and evaluation of alkali-activated concrete with thermal energy storage capability for energy geostructures

Energy geostructures, such as energy piles, tunnels, and continuous underground walls, offer an innovative solution for harnessing shallow geothermal energy while serving structural functions. However, their limited energy density often leads to inefficient heat exchange and fluctuations in structural stability, along with significant challenges related to ion erosion in practical applications. This study introduces Alkali-Activated Concrete with Thermal Energy Storage Capability (AAC-TESC), which incorporates Phase Change Material (PCM) with high thermal storage density into Alkali-Activated Concrete (AAC), for energy geostructures. For the first time, the mechanical properties, volume stability, and durability of AAC-TESC under the operational conditions of energy geostructures were systematically investigated. The results reveal that the inclusion of Thermal Energy Storage Aggregate (TESA) containing PCM significantly reduces temperature-induced deformations by 44.8-76.9 % while maintaining compressive strength within the range of 30-60 MPa, making AAC-TESC highly suitable for energy geostructure applications. Additionally, AAC-TESC shows enhanced resistance to chloride diffusion, attributed to increased thermal cycling and lower operating temperature, potentially reducing its activation energy. This study offers valuable insights into the potential of AAC-TESC to improve the volume stability and durability of energy geostructures, presenting a sustainable solution to contemporary construction challenges.