Research On The Durability Of Coral Concrete And Reliability Of Structure Life Under Island Reef Circumstance

South China Sea Islands is far away from the Mainland,without the resources of sand or freshwater,and its environment is harsh.It is of great national defense and engineering value for the study of coral aggregate seawater concrete(CASC),which are made up of corals,coral sands,seawater and cements.CASC can be used for the construction of island-reef engineering,such as port,airport,etc.However,the environment where these concrete buildings are fixed is complicated.They are suffered from compound action of various corrosion factors,including seawater immersion,spray,carbonation,dry-wet cycle and temperature change.Therefore,it is important to study the durability and structure service lifetime of coral aggregate concrete under the island reef circumstance.In this paper,the effects of dry-wet circulation and carbonization on the durability and chloride ion diffusion performance of CASC with the strength grade of C50,C60 and C65,were studied by conducting the experiments of seawater immersion,seawater dry-wet cycle test and dry-wet cycle and carbonation.It used the modified chloride ion diffusion law model to study R,C_s,D_f and time dependence index(m)of D_f for CASC of different strengths.Finally,the service life prediction of CASC structure in different exposed areas of the South China Sea islands was made,based on the design method of service life of concrete structures in the marine environments and chloride ion diffusion theory analysis software ChaDuraLife V1.0.Main results are made as follows:(1)The mass of CASC under both dry-wet cycle and carbonation gradually increase with the erosion time,and the relative dynamic elastic modulus(E_r)and ultrasonic wave velocity gradually decrease with the exposure time.Under the same exposure time,the higher the CASC strength is,the higher isE_r,the lower is the loss of dynamic elastic modulus.Under the same exposure time,the ultrasonic wave velocity had an order from high to low:C65,C60 and C50.The compressive strength of CASC is decreased by 8.8%~11%from the 28d strength.(2)The chloride diffusion of CASC accords with Fick's law of diffusion.The relationship between the exposure time and C_s followed an exponential form.The growth rate of C_s was lower than that of OPC.D_f and D_a decreased with the extension of the exposure time,and the relationship with the exposure time followed a digression law of power function.However,the dry-wet circulation and carbonation play a role in promoting the diffusion of chloride in CASC,improving D_f,D_a and time dependent index m.The dry-wet circulation increases C_s in CASC and carbonation decreases it.(3)The calculation model with different time boundary conditions has great influence on the life prediction of CASC structure under the reef environment.The principle of boundary condition selection is determined according to the significance of different power exponent models.Under the same parameter condition,the lifetime calculation result of 0.5(1-m)power function boundary condition is much longer than the life result under the(1-m)power function boundary condition.When the CASC hydraulic structure obtained the same 50 years and 100 years of life calculation results when the probability of corrosion was 10%,the protective layer thickness of the boundary condition of(1-m)is twice the thickness of the protective layer under the boundary condition of0.5(1-m)model.(4)In this paper,the(1-m)power exponent model is used to calculate the service life.When the protection layer is with the same thickness,the service life of new CASC hydraulic structure in the south China sea of different exposed areas has an order of marine atmosphere>underwater zone>tidal zone>the splash zone.The atmospheric zone C65,the underwater zone C65,the tidal zone C65and the splash zone C75 adopt 304 austenitic stainless steel bars and then coated with silane,the thickness range of the protection layer is 9.2 cm,10.5 cm,11.8cm and 10.4 cm,which can meet the service life of 20a.The atmospheric zone C65,the underwater zone C70,the tidal zone C70 and the splash zone C80 adopt 304 austenitic stainless steel bars and then coated with silane.The thickness of the protection layer is 9.2 cm,10.5cm,11.8cm and 10.4cm,respectively,which can meet the service life of 20a.The atmospheric zone C65C,the underwater zone C70,the tidal zone C70 and the splash zone C80 adopt 304 austenitic stainless steel bars and then coated with silane.The thickness range of the protection layer is 11.5~12.2 cm,5.8~7.5cm,7.2~8.2cm and 10.4~12.2cm,respectively,which can meet the service life of 50~100a.(5)The durability of the CASC hydraulic structure and architectural structure in the south China sea islands are proposed to meet the minimum protective layer thickness and minimum strength level for service time of 20a~100a.The lowest strength level of hydraulic structure of CASC is C65,with the protection layer of 7~13cm.It adopts 304 austenitic stainless steel bars and coated with silane,which can provide the service life of 50~100a.The minimum strength level of CASC construction structure is C75,with the protection layer of 2~3cm.It adopts 304 austenitic stainless steel bars and coated with silane,which can provide the service life of 50~100a.