Experimental Investigation of Gas Permeability of Concrete Lining and Membrane for CAES in Repurposed Mine Shafts

Repurposing post-mining shafts for adiabatic compressed air energy storage (ACAES) requires gas-tight lining of shaft collar. Even where macroscopic cracking is absent, the connected pore network of concrete can sustain pressure driven gas transport, leading to standby losses and reduced round-trip efficiency during long idle periods. This contribution presents an experimental investigation and measurements of candidate lining systems for shaft sealing for the A- CAES concept.

Two representative concrete samples were tested (C20/25 and C40/45), reflecting older and modern shaft linings. Two film forming surface protection systems were evaluated: (i) a thin-layer, waterborne epoxy coating WallCoat T; typical dry film thickness ~0.25 mm), and (ii) a thicker Xolutec membrane (Sikagard M 790; typical dry film thickness ~0.7–0.8 mm) that provides crack bridging capability and broader application tolerance. Specimens (Ø25 mm × 30 mm) were prepared and cured per EN 206 and EN 12390-2, with coating application and quality control aligned to EN 1504-10.

Gas permeability was determined using a steady-state flow method with helium as the measurement medium and Klinkenberg-corrected extrapolation to intrinsic permeability. Uncoated concretes exhibited mean permeabilities of ~4.6×10⁻⁴ mD (C20/25) and ~1.4×10⁻⁴ mD (C40/45). Coatings reduced permeability by 3–4 orders of magnitude: WallCoat T achieved ~3.7×10⁻⁸ mD, while Sikagard M 790 yielded ~5.0×10⁻⁷ mD with higher variability attributable to local coating heterogeneities.