Bond Behavior Between Steel Bars And Fiber-reinforced Coral Concrete

South China Sea Islands are far away from the mainland,and the cost of long-distance cross-sea transportation is huge.Therefore,it is urgent to develop a new kind of concrete that is convenient for local materials.Coral concrete has excellent properties such as local materials,high efficiency and economy,and has broad application prospects in the construction of ocean-going islands and reefs.With the increasing acceleration of the construction of South China Sea islands,more requirements have been put forward for the materials and structural properties of coral concrete.Fiber-reinforced coral concrete is a composite of fiber and coral concrete,using island coral aggregates to replace traditional coarse and fine aggregates,and introducing fiber-reinforced materials.In this paper,based on the construction needs of the South China Sea Islands,the bond behavior between steel bars and fiber-reinforced coral concrete were investigated.The main contents are as follows:(1)The mechanical performances of fiber-reinforced coral concrete were tested,and the effects of different water-binder ratio,basalt fiber content and polypropylene fiber content on the slump,compressive strength,split tensile strength and tension-compression ratio of coral concrete were studied.The results show that the two kinds of fibers can play the role of crack resistance,reinforcement and toughness on coral concrete.With the increase of fiber content,the slump of coral concrete decreases,both the compressive strength and the split tensile strength show a trend of first increasing and then decreasing,and the tension-compression ratio increases.(2)Through the bond test of steel and fiber reinforced coral concrete specimens,the effects of different water-binder ratio,basalt fiber content,polypropylene fiber content,rebar diameter and rebar surface morphology on the bond failure mode,bond-slip curve and bond strength were studied,and the mechanism of fiber in coral concrete was analyzed.The results show that the influence of fiber on the bonding performance between steel bar and fiber-reinforced coral concrete is more complicated.With proper amount of fiber,the bond failure mode tends to pull-out failure.For the deformed steel bar specimens,when the water-binder ratio is 0.25 and 0.35,the bond strength decreases with the increase of the fiber content;when the water-binder ratio is 0.4,the bond strength first increases and then decreases with the increase of the fiber content.The fiber content has a small effect on the bond strength of the smooth steel bar specimens.(3)By analyzing the bond-slip curve of rebar and fiber-reinforced coral concrete,the bond-slip curve was simplified into three parts:ascending section,descending section and residual section.The characteristic parameters of the curve were calculated:Shape parameter of ascending section α,ultimate bond stressτu,residual bond stress τ_f,and corresponding slip S_u,S_f.The bond strength calculation formula and bond-slip relationship model of fiber-reinforced coral concrete were established.