Study And Engineering Application Of CF50Pumping Concrete Filled Steel Tube With High Content Of Steel Fiber

Concrete-filled steel tube (CFST) is a kind of material which is composited by steel tube and concrete composite. With high strength, low weight and excellent resistance to deformation, it suits to big span structure greatly. In recent years, with huge appliance of large span bridge construction and increase on bridge span, shear stress of bridges arch foot can never be overlooked, especially with deck type arch-bridge.Considering the good crack resistance of steel fiber concrete, designing the lifting-up pumping of CF50concrete filled steel tube with high content of steel fiber makes more sense to big span structure if it combines the concrete filled steel, steel fiber concrete, self-compacting concrete and self-stressing concrete.This subject explores the property indicators and effect on the property by all factors for the design of C50micro-expansion self-compacting concrete-filled steel tube and CF50concrete filled steel tube with high content of steel fiber based on the new railway project of Yellow River Bridge from Suzhou to Huaigeer with cliffy sides, large span and other difficult conditions for construction.This paper explore the features of C50CFST and CF50CFST that match the characteristics of construction of pouring technology and the effect of each factors under the macro and micro-analysis. The research shows that:(1) The optimum mix ratio of C50CFST is W/C0.31,10%fly ash,8%expansion agent,40%, sand ratio,8%silicon powder,3d compressive strength≥40MPa, slump≥20cm.(2) There are two optimum mixture ratios of CF50CFST with different steel fiber volumes fraction (1.5%and2.0%). Their performance an meet the design and engineering requirements.The concrete parameter are W/C0.30,10%fly ash,8%expansion agent,60%, sand ratio,8%silicon powder and the amount of cementitious material is650kg/m3.(3) There is optimum mixing amount of sand ratio of CF50CFST. The compressive strength decreases as the sand ratio increases, while the crack resistance firstly increases but decreases later on. With the sand ratio changes from55%-64%, the extreme value of crack resistance occurs. As the sand ratio increased, slump improved accordingly, but it also lead to the increase on concrete slump and reduce of the flow speed.(4) The amount of cementitious material is crucial factor to the dispersing performance of CF50CFST and performance of concrete. As the amount of cementitious material increases, the performance of concrete improved obviously. However, when it goes beyond650kg/m3, the consistence will increases continuously, which do harm to the performance.(5) With the increase of the steel fiber, the compressive strength has no notable change, but the crack resistance increase obviously. When the amount of cementitious material reaches600kg/m, the growth of7d crack resistance with2%steel fiber slows down due to the limit for dispersing performance of steel fiber, caused by the lack of the amount of cementitious material. It will be solved as the amount of cementitious material increases to650kg/m3.(6) The amount of cementitious material increase to650kg/m3, slump of CF50CFST with1.5%steel fiber reaches19cm, while it is17.7cm under2.0%steel fiber. All the two groups of CF50CFST conform to pumping requirements but the workability of CF50CFST with2.0%steel fiber is more difficult to control.(7) From the engineering application, the C50CFST and CF50CFST of this paper show their good mechanical property and performance of shrinkage compensating, pumpability.