Mechanical performance of polyurethane polymer mortar—A novel sealing material for CAES man-made caverns

Abstract

This work aims to investigate the feasibility of polyurethane polymer mortar (PPM) as a sealing material for compressed air energy storage (CAES) caverns. The effect of polymer content, aggregates ratio (fine sand to medium sand) and filler types (bentonite, clay, and fly ash) on gas permeability, tensile strength, and resistance to high and low temperature of PPM were conducted. The scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were performed to characterize the microstructure of PPM. Additionally, numerical simulations were performed to analyze the stress distribution characteristics of PPM when used as a sealing structure. The results demonstrate that PPM exhibits low gas permeability (10⁻²¹ m²), high tensile strength (up to 2.96 MPa), and significant tensile strain (up to 27.02 %), with a relatively low elastic modulus (11.87–35.05 MPa). Meanwhile, PPM containing fly ash showed the highest strength, followed by those with clay, while PPM with bentonite exhibited the lowest strength. However, only the PPM with bentonite as a filler remained stable and did not collapse under high temperatures. The hoop stresses in the PPM are only compressive and not tensile, and the maximum hoop tensile strain remains well below the ultimate tensile strain of the material, thus preventing the tensile damage and ensuring the gas-tightness. These findings provide a theoretical basis for using PPM in CAES sealing applications, and advance the understanding and application of sealing materials in CAES man-made caverns.