Vibration mixing, characterized by the high-frequency vibrations of the mixing shaft, can enhance the mechanical properties of ultra-high-performance concrete (UHPC). However, the effects of vibration mixing on carbon nanotube (CNT)-reinforced UHPC have not been previously reported. To investigate the impact of vibration mixing on the properties of CNT-reinforced UHPC, a comparative study was conducted using different vibration mixing durations and twin-shaft mixing. The results indicate that for CNT-reinforced UHPC, vibration mixing achieves better flowability, higher wet apparent density, and superior mechanical properties in shorter mixing times compared to twin-shaft mixing, making it a more favorable method. Considering vibration mixing times ranging from 3 to 7 min, the optimal time was found to be 3 min, during which the axial compressive strength increased by 3.3%, the elastic limit tensile strength and tensile strength improved by 14.6% and 15.8%, respectively, and the initial cracking strength and flexural strength increased by 12.6% and 13.4%, respectively, compared to values after 10 min of twin-shaft mixing.

This study examines the high-temperature behavior of ultra-high-performance concrete (UHPC) formulated with aluminate cement and various fiber and aggregate combinations. Key performance metrics, including compressive strength, mass loss, hydration characteristics, porosity, and micro-structural changes, were evaluated across a temperature range of 200 ℃ to 1000 ℃. The developed aluminate cement-based UHPC exhibited stable strength development over time. Under high-temperature exposure, UHPC containing sintered bauxite sand demonstrated superior resistance to surface cracking and lower mass loss than UHPC with quartz sand. Compressive strength increased at 200 ℃ due to continued hydration and crystallization but declined significantly at higher temperatures due to dehydration and structural cracking. XRD and DSC analyses identified temperature-dependent phase transformations, leading to mass loss and strength reduction. SEM and porosity analyses revealed microstructural changes, including fiber degradation and pore expansion, particularly beyond 800 ℃. The results indicate that UHPC formulations combining both sintered bauxite sand and quartz sand with steel and PVA fibers exhibit improved high-temperature resistance.