Research On The Expansion Performance Of Core Concrete Filled Steel Tube

Concrete filled steel tube is a combination structure by stuffed steel tube with concrete.The main reason for its excellent mechanical properties is the cooperating function between the steel tube and the core concrete.In order to achieve this aim,both of them must be combined closely.Due to the shrinkage of concrete and lack of curing water,the core concrete and the wall of steel tube are inclined to separate and form a cavum,may bring the hidden trouble.To solve the problem of concrete cavum, this paper researched the expansion performance of concrete at closure conditions.Effects of different water-binder ratio,water quantity and haydites on expansion performance of concrete have been studied.With actual enggering mix, effects of different binder materials on the expansion performance of concrete have been compared.Through experimental study, these conclusions could be got:(1)To the mortar, water-binder ratio within 0.31～0.33, exist best water-binder ratio to get max expansion ratio. The percentage of expansion will be improved with increasing water and mixing saturated haydite at low water-binder ratio,and will be reduced with increasing water at high water-binder ratio.Mixing saturated haydite won't influence the percentage of expansion at high water-binder ratio.The expansion of low-heat portland cement is higher than rapid-hardening sulphoaluminate cement at all ages with the same amount of saturated haydite. The expansion of martar with II fly ash and S95 slag are similar.(2)The saturated haydite will improve the expansion of concrete, and followed by:large haydite>small haydite>general aggregate.(3)Comprehensive results of this study, the concrete made of low–heat portland cement concrete 30% saturated haydite and 8%MgO expansion admixture have better expansion property when concrete is curing at closure condition and the water-binder ratio is 0.31, and the expansion of concrete will have a sustained and stable development.(4)Curing conditions affect the expansion performance of concrete,so it is incorrect to use expansion ratio of concrete filled steel tube with curing in water and air,and the expansion performance of concrete filled steel tube should be judge by the expansion ratio of concrete with curing at closure conditions.