A modified approach for measuring the air permeability of ultra-high performance concrete (UHPC) under vacuum conditions

This study proposes a novel test method of the air permeability measurement under extreme vacuum condition to examine the performance of materials for Hyperloop tubes. Tests on cement-based materials demonstrated that the developed test setup was effective in measuring air permeability in extreme vacuum conditions. The results show that ultra-high performance concrete (UHPC) has significantly lower air permeability (10(-18) m(2)) in vacuum conditions than other cement-based materials (10(-16) m(2)) due to its dense microstructure and reduced pore size, which were within the range of previous results (10(-18)-10(-16) m(2)). The measured porosity results had a strong correlation with air permeability (R-2 > 0.97), validating the suitability of the proposed method for measuring the air permeability of cement-based materials in vacuum conditions. These findings provide fundamental material properties for the design of Hyperloop tube structures.