Research On The Preparation Technology,Durability And Mechanical Properties Of Concrete Members Of High Strength Coral Aggregate Seawater Concrete

South China Sea Islands is far away from the Mainland,where is no sand and freshwater resources and the environment is harsh.So there has a scientific significance,a national defense and an engineering value for CASC made up of corals,coral sands,seawater and cements,and which is used for the construction of island-reef engineering,such as a port or an airport,etc.Investigation and research on durability of CAC structure in tropical island environment,the preparation methods,basic mechanical properties,diffusion law of chloride ion,corrosion behavior of reinforced and mechanical properties of reinforced CASC were studied,the mechanism of its durability deterioration and its mechanical properties were investigated,which provide a raw material localization and low cost high strength CASC preparation method and steel bar corrosion protection technology for the construction of South China Sea islands and reefs engineering.The main research contents and results are as follows:?1?Based on the literature investigation and field surveys of various CAC structures in the tropical islands and reefs,main destruction,corrosion ratio and diffusion law of chloride ion were studied.The results showed that:Marine environment has the function of corrosion damage of CAC structure is strong,the main failure characteristics of concrete cover crack,collapse,steel bar exposed,steel corrosion.In different exposed area C_s,D_a and D_f distribution were atmosphere zone>underwater zone>splash zone.D_a of CAC was 1-8 times larger than OPC.S_plash zone and underwater zone were respectively 15 and 7.4 times the atmospheric zone of CAC D_a in the South China Sea.?2?For the purpose to explore fcu of CASC influence of total cementations material,pre absorption rate,sand ratio,net W/B,based on the theory of slurry concrete and the design principle of high performance LAC.The results show that:For fcu of CASC,various influence factors from large to small order:Pre absorption rate>net W/B>SP>total cementations materials,and fcu increases with the increase of total amount of cementations materials,with the decrease of pre absorption rate,S_p and net W/B.By unweathering coral,S_p is 70%,the pre absorption rate is 5%,the total W/B is 0.2?0.3,the amount of cement is 600 kg/m³?800 kg/m³,mineral admixture amount is 20%?25%,it can achieve the highest fcu?C55?.?3?The whole stress-strain curves of CASC were studied by using prismatic specimens under uniaxial compression.The equal stress cycle loading and unloading and equal strain monotonic loading methods were adopted.The results showed that:The crack of CASC directly through coral aggregate continues to spread,CASC has the rapid destruction of brittle nature when the specimen strain reach ?oi,typical damage state is splitting failure.This paper presents the two-part constitutive equation of CASC which can reflect all the characteristics of compression test.CASC is more brittle than OPC and LAC in same strength grade.With the increase of strength grade,E,of CASC is increase trend,the ? of CAC first increases and then reduces.?4?The influence of different concrete grades,cement type,curing age and exposure time on the diffusion of chloride ion of CASC was studied in seawater immersion environment by the natural diffusion method.The results show that:The chloride diffusion of CASC accords with Fick's law of diffusion.CASC R increased with the extension of the curing age.C_s and D_a decreased with the extension of the curing age.The relationship between the exposure time and C_s followed an exponential form,however,its growth rate was considerably lower than that of OPC.Furthermore,the decreasing relationship between D_a and the exposure time conformed to the power function.The CASC Za exposed for 10 a-25 a under a laboratory simulated marine environment was 88.9%?99.1%lower than that in an actual marine environment.?5?With LPR and EIS,Factors affecting corrosion reinforcement in CASC were researched,including coating thickness,exposure time,reinforcement types,inhibitor and concrete strength grades.The results show that:The EEC circuit codes in a CASC reinforcement electrode were R_s?C_cR_c?(Q_dlR_ct)in the passivation stage and R_s?C_cR_c?(Q_dl(R_ctW))in the corrosion stage.In order to reduce the corrosion risk of steel bars,a coating thicker than 5.5 cm and a concrete strength grade over C50.With increased exposure time,the decreasing rate of effect of CN was higher than that of AA,and the pre-absorbed inhibitor could improve resistance capabilities.In the marine environments,the corrosion resistance of different CASC reinforcements followed the rule:2205 duplex stainless steel>316 stainless steel>organic new coated steel>zinc-chromium coated steel>common steel.?6?The flexural behavior and shear behavior of coral aggregate reinforced concrete beam were tested to investigate the crack development,failure mode,mid-span deflection and flexural capacity on the influence of different concrete types,concrete strength grades,reinforcement ratios and reinforcement types.The results showed that:With the increase of the reinforcement ratio,concrete strength and reinforcement strength,both M_cr and M_u of coral aggregate reinforced concrete beam would gradually increase.In consequence,the extension of crack width would gradually slow down.The formulas in JGJ 12-2006 and GB 50010-2010 were proved to be applicable in the calculation model of coral aggregate reinforced concrete beam flexural capacity.Besides,selection rule of parameters was also determined in this paper.The results showed that:The cracking load(V_cr),inclined crack load and shear strength(V_cs)of coral aggregate reinforced concrete beam increased with the concrete strength grades.The serious corrosion of common steel in the coral aggregate reinforced concrete beam,degraded the flexural rigidity to some degree.In the initial loading stage,flexural cracks occurred at normal section near mid-span of the beam with slow development of crack width.Whereas as the load increased,inclined cracks were formed from the support to the concentrated force point of action,which widened rapidly,leading to the failure.Meanwhile,a more reasonable calculation model of coral aggregate reinforced concrete beam shear capacity was proposed after being validated by the tests and reference data.?7?Take concrete type,concrete strength grade,reinforcement type and initial eccentricity as the parameter,tests on the compression behavior of coral aggregate reinforced concrete colum were conducted to investigate the fracture development,failure shape,deformation and bearing capacity of coral aggregate reinforced concrete colum.The results showed that:Under the same mix ratio,the lateral stiffness and ductility of coral aggregate reinforced concrete colum are worse than ordinary Portland reinforced concrete colum.Under the same load,steel bars in coral aggregate reinforced concrete colum share more load than steel in ordinary portland reinforced concrete colum.The N_u of common steel coral aggregate reinforced concrete colum?C60?is about 7.1%?20.8%higher than that of organic new coated steel coral aggregate reinforced concrete colum?C60?.Considering the influence of rebar corrosion and coating steel slip on coral aggregate reinforced concrete colum axial compression,small eccentric compression and large eccentric compression N_u,a calculation model of coral aggregate reinforced concrete colum axial compression,small eccentric compression and large eccentric compression N_u is put forward,which meets the requirements of high strength and high durability.