Integrated static-dynamic and microstructural investigation of tensile performance in fibre-reinforced lunar concrete under cryogenic temperatures

As lunar exploration progresses, the construction of resilient structures on the Moon becomes increasingly critical. Given the Moon’s severe environmental conditions, it is essential to assess the mechanical behaviour of candidate structural materials under relevant stress states. This study conducted the static and dynamic split-tensile tests using a split Hopkinson pressure bar apparatus. Lunar regolith simulant-based ultra-high performance alkali-activated concrete, reinforced with steel and polyoxymethylene (POM) fibres in mono and hybrid configurations, was synthesised to mitigate the inherent brittleness of the geopolymer matrix. Experiments were performed over a temperature range from 20 °C to -170 °C and at the strain rates of 30-90 s -1 , aiming to simulate lunar service conditions and evaluate the material’s tensile performance. The results indicate that all specimens exhibited strength enhancement and pseudo-ductile behaviour under static loading, with steel fibres delivering superior performance and POM fibres offering high reinforcement mass efficiency. Dynamic tests confirmed pronounced strain-rate sensitivity, especially at sub-zero temperatures. Steel fibre mixes achieved the highest strength of 31.6 MPa at -170 °C and 90 s -1 , while POM fibres exhibited the highest strength gain per unit fibre mass under dynamic loading, despite their reinforcement effectiveness was markedly degraded under cryogenic conditions due to fibre embrittlement. Dynamic failure modes were strongly affected by the fibre type, strain rate, and temperature, with mono POM specimens exhibiting extensive cracking and severe fragmentation, indicating a loss of crack-bridging capacity due to cryogenic fibre rupture. The microstructural images revealed potential ice-filled pore, particularly in POM mixtures. Dynamic increase factor (DIF) demonstrated strong rate sensitivity under cryogenic exposure, and simplified DIF-rate-temperature models offered a practical predictive framework for lunar infrastructure applications in extreme environments. • Splitting tensile behaviour of UHP-LAAC was tested under ambient and cryogenic conditions. • Both quasi-static and dynamic strength increased with decreasing temperature. • Strain-rate sensitivity was enhanced at sub-zero temperatures, especially for steel fibre mixes. • SEM and CT analyses revealed cryogenic fibre degradation and potential ice-filled pores.