Experimental Study On Bond Behavior Between CFRP Bars And Coral Concrete Specimens And GFRP Bars And Coral Concrete Specimens Immersed In Seawater

The compressive strength of coral concrete(Coral aggregate concrete)obtained by mixing natural coral debris with seawater can reach 20 to 40 Mpa.Coral concrete can not only be applied to island revetment projects such as slope protection,wharf,breakwater,but also can be applied to road engineering as rigid cushion for roads.The application of the coral concrete can not only meet the local demand in the far island construction,but also can save money and shorten the construction period.here are two reasons for the relatively few researches and applications of coral concrete.First,the low demand for the construction of the island reefs caused by the weak awareness of the protection of marine rights and interests for a long time;second,there is a large amount of salt in the wet and hot water and in the coral clastic concrete,which can easily cause the corrosion of the steel bars.Based on this background,coral concrete is used instead of ordinary concrete,CFRP bar and GFRP bar instead of reinforcing bars.The bonding properties of CFRP bar coral concrete and GFRP bar coral concrete under seawater immersion were studied,which lays the foundation for the application of coral concrete in the construction of offshore islands and reefs.In this paper,the basic mechanical properties of coral concrete and FRP tendons are studied and analyzed,and Then the experimental study on the bond behavior between CFRP bar and coral concrete and GFRP bar and coral concrete was carried out by seawater immersion.At the end of the paper,the effects of seawater immersion time,fiber reinforcement,fiber diameter,coral concrete protective layer thickness and coral aggregate on the bonding properties of FRP tendons and coralline concrete interfaces were discussed.The research results will not only lay a theoretical foundation for the practical application of coral concrete in the South China Sea Island and reef engineering,but also improve and develop the related conclusions of the application field of coral concrete.The main research contents are shown as follows.1.After immersion in 120 d at 30 degree seawater,the micro cracks and porosity of CFRP bars are much smaller than those of GFRP bars.This is mainly due to the stable chemical properties of carbon,and no obvious damage to the carbon fiber itself.Only a partial detachment of the matrix on the surface of CFRP bars occurs.Under long-term seawater immersion,the mechanical properties of CFRP bars are better than those of GFRP bars.2.The ultimate bond strength between FRP tendons and coral concrete increases and then decreases with the increase of soaking time,and the rate of later decrease gradually slows down.Unlike the failure modes of CFRP tendons and coral concrete specimens,with the increase of soaking time,the failure mode of GFRP tendons and coralline specimens gradually changed from the reinforcement to the fracture of the tendons.With the increase of soaking time,the ultimate bond strength of FRP tendons-coralline concrete increased first,then decreased,and the later decline rate gradually slowed down.The failure mode of some GFRP tendons-Coral concrete specimens gradually changed from ribbed out to ribs fracture.3.Under long-term seawater immersion,the retention rate between CFRP bars and coral concrete is higher than that of GFRP bars and coral concrete.Increasing the thickness of the protective layer is conducive to slowing down the corrosion of FRP harmful materials in seawater.Compared with CFRP bars and coral concrete,increasing the thickness of protective layer is beneficial to maintain the bond between GFRP bars and coral concrete.