Dynamic compression behaviour of innovative geopolymer-based lunar ultra-high performance concrete under ambient and cryogenic temperatures

The rapid advancements in science and technology have accelerated efforts towards establishing sustainable extra-terrestrial habitats, with ultra-high performance concrete (UHPC) emerging as a promising candidate for constructing lunar bases due to its excellent mechanical and durability properties. This study employed a split Hopkinson pressure bar (SHPB) device to examine the dynamic compression behaviour of lunar regolith simulant-based UHPC (LUHPC), focusing on the effects of fibre type (steel and polyformaldehyde), fibre combinations (mono and hybrid), testing temperatures (20 °C ∼ -170 °C), and strain rates (50-200 s^-1). The results revealed that cryogenic conditions markedly enhanced the static compressive strength (up to 20.6%) and elastic modulus (up to 13.7%) of steel fibre-reinforced LUHPC. Polyformaldehyde fibres yielded moderate improvements but attained a higher specific strength at -70 °C. Under dynamic loading, steel fibres exhibited pronounced strain-rate and temperature sensitivity, reaching a peak strength exceeding 280 MPa at -170 °C, achieving a dynamic increase factor from 1.137 to 1.630 as strain rates increased to 200 s^-1, and improving impact energy absorption by up to 179.1%. In contrast, the polyformaldehyde fibres showed modest improvements and heightened brittleness at extreme temperatures. The failure patterns varied with strain rate and temperature, with steel and hybrid fibre reinforcements effectively mitigating fragmentation at sub-zero temperatures. The existing predictive models overestimated strain-rate effects at 20 °C, whereas the newly derived empirical equations accurately captured LUHPC behaviour under both ambient and cryogenic conditions. Future work will focus on evaluating the static and dynamic performance of LUHPC with lunar-derived reinforcement materials under extreme thermal cycles to further support its applications in extra-terrestrial infrastructure.