Frost Resistance of Steel Fiber Reinforced Micro-Expansive Concrete Filled Steel Tube

This investigation was done based on the concrete filled steel tube (CFST) winter construction of Ganhaizi Bridge. Steel fiber reinforced micro-expansive concrete (SREC) with high frost-resistance ability, excellent fluidity and good self-compacting ability was prepared. Strength development mode under low temperature was illustrated. Scanning electron microscope (SEM) was used to analyze the morphology features of hydration products at the age of 28 days. It was confirmed that when the content of sodium nitrite was 0.4%, SREC did not frost under -5°C. In addition, SEM showed that ettringite and CSH gels were in good growth state, and concrete structure was very dense. Furthermore, 6 CFST short columns were poured in the winter construction site of Ganhaizi Bridge, and another 27 short columns were cut from emitting slurry pipe filling with concrete emitted from main girder. The bearing capacity of all the CFST specimens was tested when the environment temperature rose to about 25°C. The experimental results indicated that the mechanical performances of CFST specimens with anti-freezing admixture did not exhibit degradation when cast in site under a low temperature and tested at 24.3°C. The concrete presented in this research substantially met the need of Ganhaizi Bridge CFST construction in winter.