Experimental Research On Composite Action Of Seawater And Sea Sand-coral Aggregates Concrete Filled RPC-FRP Tube

The use of seawater,sea sand and other marine resources for producing concrete can significantly reduce the consumption of freshwater,river sand and other natural resources.It is very important in island construction,and it gains much attention nowadays.However,much salt in seawater and sea sand will cause the corrosion of steel bars and lead to durability problem of concrete structures.Therefore,a prefabricated tube is designed for combining with seawater and sea sand concrete in the paper that it composed by spiral fiber reinforced polymer(FRP)hoops and reactive powder concrete(RPC)and named as RPC-FRP tube.The tube has an excellent load carrying capacity and durability.In constructing site,seawater and sea sand-coral aggregates concrete(SWSSCAs),composed of coral aggregates,seawater,sea sand and other cementing materials,is choosed as filler in RPC-FRP tube.This novel structure is named as SSCAs-RPCT column.In this hybird system,FRP spiral stirrups provide efficient lateral confinement for the inner concrete,which result in high axial capacity and ductility of column.On the other hand,RPC tube can directly carry considrable axial load under the peak load attributed to its super-high compressive strength.The prefabricated tube is also the permanent formwork and temporary support during construction.Therefore,application of SWSSCAs is attractive alternative for infrastructure development in mid-ocean islands and offshore sites in order to avoid the long-distance marine transportation of materials.In order to investigate the axial compressive performance of SSCAs-RPCT columns,total 22 SSCAs-RPCT columns and one hollow RPC tube were conducted axial compression test.The test parameters included the type of spiral hoops,the stirrup spacing in RPC-FRP tube,and the internal seawater and sea sand-coral aggregates concrete strength.The investigation and analysis focused on axial capacity,failure mode and deformation.Based on the test results and analysis,the following conclusions are summarized:(1)SWSSCAs columns exhibited a multi-crack failure mode on the surface of RPC tube without obvious peeling of RPC cover.The RPC tube in the composite column can maintain its own integrity in the whole loading process due to the bridging reinforcement action of stainless steel fibers.(2)Specimens with BFRP hoops showed higher performances in both bearing capacity and ductility compared with specimens with CFRP hoops with the similar confinement degree.(3)Compressive performance of SWSSCAs columns improved effectively as the volumetric FRP hoop ratio in RPC tube increases.(4)The confinement effect is relatively obvious for the SSCAs-RPCT columns filling with low strength SWSSCAs compared with the columns filling with relatively higher strength SWSSCAs,while it has no similar regularity for ductility.The strength mechanism of this novel structure is much different from others.Due to the considerable axial capapcity of RPC cover,existing classic caculation models of confined concrete were inapplicable to SSCAs-RPCT columns.Based on experimental findings and existing confinement model s,a special load carrying capacity model is proposed for SSCAs-RPCT columns,in which the axial load directly carried b y RPC cover is also counted.The proposed model exhibits accurate prediction under the current test conditions.