Experimental Study On The Mechanical Properties Of Self-compacting Recycled Steel Tube Concrete Short Columns

Steel pipe self-compacting recycled concrete column is a combined structure that can comprehensively reflect the superior working performance of self-compacting concrete and the strong restraint performance of steel.The combination of the two can slow down people’s consumption of natural resources,respond to the national green sustainable development road,reduce the impact of low strength of recycled concrete on the building structure,delay the cracking of core concrete,improve its strength and plasticity,and avoid steel pipe.Considering the difference in concrete strength in abandoned buildings,abandoned concrete on a pavement is used as recycled coarse aggregate.In this paper,the workability and mechanical properties of self-compacting recycled concrete were studied in terms of different replacement rates of recycled aggregates(0%,50%,100%)and different expansion agents(0%,6%,9%,12%).For self-compacting recycled concrete of steel pipe,7 axial compression test pieces and 14 bias test pieces were designed and manufactured,whose test variable are recycled aggregate replacement rate(0%,50%,100%),expansion agent dosage(0%,6%,9%),steel content(13%,18%,22%)and eccentricity(Effect of 20 mm,40mm).The effects of test variables on the mechanical properties such as stiffness and ultimate bearing capacity of the specimen and the deformation properties such as ductility coefficient and energy dissipation coefficient were studied.The bearing capacity of the test piece was calculated by using various concrete-filled steel tube design rules,and the calculated bearing capacity was compared with the measured bearing capacity of the test piece.The calculation formula of the bearing capacity corresponding to the measured value and the measured value was obtained through comparative analysis.The results show that the change of the expansion agent dosage and the replacement rate of recycled aggregate have certain influence on the workability and mechanical properties of the concrete.Increasing the amount of expansion agent and the replacement rate of recycled aggregate,the working performance of the concrete mixture is reduced to varying degrees,and the change of the amount of expansion agent has a great influence on the working performance of the concrete mixture.The partial mechanical index of self-compacting recycled concrete shows an increasing trend with the increase of the amount of expansion agent.For the self-compacting recycled concrete specimens of steel pipes,increasing the replacement rate of recycled aggregates will cause the ultimate bearing capacity and stiffness of the specimens to decrease to some extent,but the ductility coefficient and energy dissipation coefficient of the specimens can be improved to some extent.The addition of an appropriate amount of expansion agent can increase the ultimate bearing capacity and rigidity of the test piece,but it will reduce the ductility and other deformation properties of the test piece.Increasing the steel content,the mechanical properties such as the ultimate bearing capacity and stiffness of the test piece,as well as the ductility coefficient and the energy dissipation coefficient are greatly improved.The bearing capacity calculated by BS5400,CECS28:2012,GB50936-2014,GJB4142-2000 and DBJ13-51-2003 is compared with the measured bearing capacity.It is found that the bearing capacity calculated by GB50936-2014 is the closest to the measured value and relatively safe.The calculation results are relatively stable.It is recommended to use GB50936-2014 to calculate the bearing capacity of self-compacting recycled concrete short columns.