Design and Characterization of a Low-Magnetoresistance, High-Stability Concrete for Ultra-High-speed Low-Vacuum Tube Infrastructure

The low-vacuum, pressure-cycling, and strong magnetic field environment of vacuum-tube maglev systems presents considerable challenges for structural material design. This study develops a class of low-vacuum tube concrete (LVTC) featuring high strength, high toughness, and low magnetic susceptibility, based on dense particle packing, polymer modification, and fiber reinforcement principles. The effects of atmospheric drying (AD), continuous low-vacuum drying (VD), and cyclic low-vacuum/atmospheric drying (CD) on the macro-micro properties of LVTC were systematically investigated. The results show that low-vacuum conditions increase the brittleness and shrinkage of concrete. The addition of redispersible latex powder and modified emulsified asphalt was effective in mitigating brittleness, reducing shrinkage, and decreasing impermeability. Among the tested fibers, polyethylene fibers significantly outperformed basalt and glass fibers in enhancing mechanical performance under vacuum exposure. CD exhibited intermediate effects on strength, moisture migration, and pore structure compared to AD and VD, primarily influenced by vacuum exposure duration. SEM analysis revealed that the viscoelastic fiber-flexible film-matrix network plays a key role in suppressing vacuum-induced shrinkage cracking. Magnetic induction tests confirmed that all constituent materials are weakly magnetic (<30 nT), and the incorporation of silica fume and polymers further reduces magnetic susceptibility. These findings provide a scientific basis for the design of LVTC, supporting the development of next-generation high-speed vacuum maglev infrastructure.