Dynamic behaviour of geopolymer-based ultra-high-performance concrete at low and cryogenic temperature

This study investigates the mechanical behaviour of geopolymer-based ultra-high performance concrete (GUHPC) under coupled extreme low temperatures (−160–20 °C) and dynamic loads. The research utilised a Φ100-mm split Hopkinson pressure bar (SHPB) technique for dynamic testing. Dynamic impact experiments were conducted at temperatures of 20, −70 and − 160 °C, with strain rates ranging from 40 to 160 s⁻¹ for compression tests and 20 to 80 s⁻¹ for splitting tensile tests. Results reveal that both compressive and splitting tensile strengths of GUHPC increase as temperature decreases and strain rate increases. The dynamic increase factor (DIF) for both compression (${\mathrm{DIF}}_{f_c^{\prime }}$) and tension (${\mathrm{DIF}}_{f_t}$) was found to be higher at low temperatures and cryogenic condition. The ${\mathrm{DIF}}_{f_c^{\prime }}$values at −70 °C and − 160 °C were approximately 12 % and 22 % higher, respectively, as compared to the values at 20 °C with the strain rate of 160 s⁻¹. The ${\mathrm{DIF}}_{f_t}$ at −70 °C and − 160 °C were 35 % and 47 % higher, respectively, in comparison with the room temperature values at a strain rate of 40 s⁻¹. The study also examined the material microstructural change, failure modes, energy absorption capacity, and developed empirical formulae for predicting the DIF at various temperatures. X-ray computed tomography (CT) scans revealed distinct microstructural changes in GUHPC under various temperatures, illustrating ice formation, pore structure alterations and microcracking, particularly at cryogenic temperatures. These findings contribute to the understanding of GUHPC behaviour in extreme environments and have implications for its application in cryogenic structures subjected to impact loading.