Mechanical Properties and Gas Permeability Characteristics of Airtight Concrete for Sealing Layer in Compressed Air Energy Storage Underground Caverns

Compressed air energy storage (CAES) is a promising large-scale energy storage technology, but its efficiency and safety depend critically on the sealing performance of underground caverns. From a building materials science perspective, a key challenge is to develop cement-based sealing materials that maintain low gas permeability and mechanical stability under coupled thermo-pressure cycles. However, the gas permeability evolution and microstructural mechanisms of sulphoaluminate cement-based airtight concrete under such conditions remain insufficiently understood. To address this problem, this study developed an airtight concrete for CAES cavern sealing layers, based on sulphoaluminate cement with fly ash, slag, basalt fiber, and chemical admixtures. Mechanical properties, gas permeability, and microscopic mechanisms were evaluated through uniaxial compression and tensile tests, gas permeability tests under different thermal-pressure cycles and pore pressure conditions, and SEM/DEM analysis. The material exhibits a compressive strength of 62.59 MPa and good airtightness. Under 60 °C cycling, Permeability remained on the order of 10−18 m2, following the Klinkenberg gas slippage model. Microscopic analysis suggested a dense structure with limited visible pore connectivity. COMSOL Multiphysics preliminarily indicated that, under assumed design conditions (e.g., the Three Gorges Ulanqab project), the sealing layer remained in triaxial compression with an estimated gas leakage rate below 1%, demonstrating satisfactory sealing performance and structural stability within the investigated operational period. This study provides a theoretical basis and experimental support for sealing material design in CAES caverns.