Shear Behaviour Of Seawater Sea-sand Coral Aggregate Concrete Beams Reinforced With CFRP Strip Stirrups

In the island construction project,the preparation of concrete for remote islands or extreme region using locally available seawater,sea sand,and coral aggregate which can reduce the construction time,improve construction efficiently and mitigate the shortage of river sand and natural gravel resources.FRP is suitable for marine environments due to its excellent corrosion resistance and high tensile strength.At present,the composite of coral concrete beams and FRP is often made of FRP longitudinal reinforcement to study its flexural properties,the research of FRP transverse stirrup combined with coral concrete beams is less.This study is the first to experimentally investigate the shear behaviour of seawater sea-sand coral aggregate concrete beams reinforced with CFRP(carbon fibre-reinforced polymer)strip stirrups.The traditional reinforced concrete beam’s stirrups are replaced by CFRP strip stirrups processed by FRP sheet materials,and CFRP strip stirrups are formed in seawater sea-sand coral concrete beams.It avoids the fiber bending which caused by the overlap area slip or the early damage occurring in the bending position because of bearing shear.A total of 11 beam specimens were designed,the test parameters included concrete type,concrete strength,and stirrup configuration,the shear properties of CFRP strip stirrup and seawater sea-sand coral aggregate concrete under various loads were analyzed.The results show that:(1)Coral concrete beams early stiffness change is slightly less than ordinary concrete beams,the load at the time of cracking is larger,but the final bearing capacity is smaller than ordinary concrete beams,this is because coral concrete aggregate has a certain brittleness,deformation ability is small,after the diagonal shear cracks appears,they penetrated directly through the coral aggregates and split them in half,the aggregate interlocking effect is lost,when cracks through the concrete quickly destroyed.Differed greatly from those in the ordinary concrete beams,where the major shear cracks bypassed the natural gravel aggregates and extended along the aggregate-mortar interfacial transition zone.(2)The ultimate shear bearing capacity of the specimen beam increases with the increase of concrete strength.When the specimen beam is loaded until the first shear crack appears,the shear force was mainly carried by the concrete.After the crack appears,the stirrups gradually participate in resisting the shear,and increasing the strength of concrete has a positive effect on the shear contribution value of concrete.(3)The shear failure of beams reinforced with CFRP strip stirrups was characterised by the brittle failure mode of the sudden rupture of CFRP strips’ bend portions.The shear performance of the stirrup beams with CFRP strip stirrups is excellent,and the crack restraint effect is better than ordinary stirrup beams.The cracking load and ultimate bearing capacity of the stirrup beams with equal stiffness replacement method are improved,in the equal strength replacement method,the shear efficiency of strips is low.The strain on the same stirrup is different,and the largest place is concentrated at the intersection of the critical diagonal shear crack and the stirrup.