Experimental Study On Mechanical Properties Of Recycled Aggregate Concrete Filled Square Tube Short Columns

Recycled aggregate concrete provides a solution to dealing with natural aggregateshortage and construction waste accumulation, which has got attention in domestic andoverseas. Up to now, recycled aggregate concrete is widely used in building construction.Compared to ordinary concrete, recycled aggregate concrete has certain flaws, it mayeffectively change recycled aggregate concrete’s flaws such as low intensity and poordurability by combining recycled aggregate concrete with concrete filled steel tube, whichhas become a research focus. However, the current research on recycled aggregate concretefilled steel tube is mainly focused on axial compression specimens, only a relatively smallnumber of research is about eccentric compression specimens. Based on the study of themechanical properties of recycled aggregate concrete under different aggregatereplacement ratio, this paper have an experimental study on the mechanical properties ofrecycled aggregate concrete filled steel tube eccentric compression specimens. The maincontents are as follows:(1) Using pre-absorbent method for the machined recycled aggregate and applying theordinary concrete’s mix formula in “Ordinary concrete mix design procedure” to designrecycled aggregate concrete mixing ratio. The results show that the workability of newlymix recycled aggregate concrete is same as ordinary concrete, which also have a goodcohesiveness and water retention.(2) The mechanical properties of recycled aggregate concrete under differentaggregate replacement ratio are studied in the test, including cube compressive strength,axial compressive strength, splitting tensile strength and modulus of elasticity. The resultsshow that the cube compressive strength, axial compressive strength, splitting tensilestrength and modulus of elasticity are decreasing as the aggregate replacement rateincreases. However, there is a slight increase on cube compressive strength, axialcompressive strength as the aggregate rate is50%.(3)5axial compression specimens and10eccentric compression specimens aredesigned in the monotonic loading test, which is used to study the impact of aggregatereplacement ratio and eccentricity on recycled aggregate concrete filled steel tube’s carrying capacity and deformation properties. The results show:①Recycled aggregatereplacement rate has no influence on the failure mode of the specimen, axial compressionspecimens’ failure mode is shearing failure, while eccentric compression specimens’ isbending failure;②With the increasing of aggregate replacement ratio，there is a smalldecline of specimens’ ultimate bearing capacity, but the ultimate bearing capacitydecreased significantly with the increasing of eccentricity;③Through the load-deformation curves and load-strain curves, the sectional strain distribution is well complywith the plane assumption, with the increasing of recycled aggregate replacement ratio,specimens’ deformation and strain increased accordingly, and the deformation performanceimproved, after reaching the ultimate bearing capacity the specimens have a good ductility.(4) Based on the test data and structural design procedures in domestic and overseasof concrete filled steel tube, the formulas of capacity and initial stiffness are given, whosecalculated values are basically the same with measured values.