Mechanical Properties and Compressive Constitutive Model of CAES Cavern Lining Concrete under Thermomechanical Coupling Effect

Compressed air energy storage (CAES) is an emerging large-scale energy storage technology, in which the lining concrete structures of underground caverns are subjected to simultaneous thermal and pressure cycling loading during operation. The deterioration of mechanical properties of concrete materials under coupled thermal–mechanical loading will affect the stable operation of CAES underground caverns. To study the stress–strain characteristics of lining concrete in CAES caverns under thermomechanical coupling, we conducted thermomechanical cyclic loading tests, uniaxial compression tests, and scanning electron microscope (SEM) tests. We studied the influence of thermomechanical coupling effects on the mechanical properties and microstructure of concrete, with the objective of providing insights and guidance for the design of lining concrete structures in CAES caverns. The results indicate that under thermomechanical coupling, the compressive strength of concrete gradually declines with the increase in the number of cycles and cyclic temperature. Thermomechanical coupling exacerbates the deterioration of concrete’s mechanical properties, resulting in a significant reduction in compressive strength compared to that under single loading. Under thermomechanical coupling loading, the propagation and interconnection of microcracks in the interfacial transition zone between aggregates and cement mortar are the primary factors contributing to the decline in concrete’s mechanical properties. A compressive constitutive model for concrete under thermomechanical coupling was established. The damage evolution curve of concrete reveals that the coupled thermal–mechanical effect accelerates the damage rate of concrete, with the damage rate gradually increasing as the cyclic temperature rises. The impact of the number of cycles on concrete is primarily observed during the initial stages of cyclic loading. This paper aims at providing a reference for the design of lining concrete structures in CAES caverns.