Experimental Study On The Bonding Performance Of Full Coral Aggregate Seawater Concrete With FRP Bars

In the construction of the South Island Reef project far from the mainland,the use of coral aggregates made of full coral aggregate and seawater is one of the effective means to solve the scarcity of construction materials in the development of marine engineering.The application of all-coral aggregate seawater concrete is of great significance for the construction of remote island reef projects.This article has carried out three parts of experimental research: First,orthogonal test was used to mix the whole coral aggregate seawater concrete with specific compressive strength to study the mixing method and strength growth law of the whole coral aggregate seawater concrete;Secondly,the mechanical property degradation of BFRP bars under high temperature and high humidity and coral concrete environment was studied by using FRP bars tensile test.The effects of temperature,erosion age and concrete type on the mechanical properties of BFRP tendons were analyzed.Using Fick and Arrhenius degradation models to predict the life of BFRP bars in coral concrete.Third,the central pull-out experiment was used to study the influence of many factors on the bonding performance.Including FRP bar type,concrete type,FRP bar surface form,coral concrete strength,relative protective layer thickness,FRP bar diameter,FRP bar bond length,hoop restraint,etc.Based on the experimental data and the existing classical FRP bars and concrete bond-slip constitutive model,a three-segment bond-slip constitutive model that conforms to FRP bars and full coral aggregate seawater concrete is established.Finally,the basic anchoring length formula of FRP bars and coral concrete was derived.The main conclusions of this thesis are as follows:(1)None of the existing mix concrete design theories of ordinary and lightweight aggregate concrete is applicable to the mix ratio design of full coral aggregate seawater concrete.At present,the proportion of full-coral aggregate seawater concrete is usually obtained by adapting.From the orthogonal test range analysis,it can be found that the factors that affect the compressive strength of the whole coral aggregate seawater concrete 28-day cube from large to small are: cement amount> sand rate> artificial seawater amount> coralstone amount.The compressive strength of the whole coral aggregate seawater concrete in the first 3 days can reach more than 70% of the compressive strength of the 28-day cube,and 7 days can reach more than 80% of the compressive strength of the 28-day cube.There was still aslight increase in intensity after 28 days.(2)Temperature plays a crucial role in the degradation of BFRP tendons in coral concrete.Under normal temperature environment,BFRP tends to have a certain degree of mechanical property degradation only in the first cycle,and there is little mechanical property attenuation in the later period.In marine environment,the degradation of mechanical properties of BFRP tendons in coral concrete is an external process.The initial degradation rate is faster and the later degradation is slower.(3)The main reason for the deterioration of the mechanical properties of BFRP tendons in concrete is the erosion of BFRP tendons fibers and resin by the strong alkaline concrete pore solution.Erosion of the fiber causes the breakage of some fiber bundles,and erosion of the resin causes the weakening of the fiber bundle's cooperating force.Under the same environment,the ultimate tensile strength of BFRP bars in full-coral aggregate seawater concrete decreases more than ordinary concrete in each cycle.This may be due to the poor anti-permeability of full-coral aggregate seawater concrete.Solution contact results more fully.(4)The limit adhesion of light round BFRP and GFRP bars is similar to that of full-coral aggregate seawater concrete,which is about three times that of CFRP bars;The ultimate bonding strength of light round BFRP bars and ordinary concrete is only about 1/5 of its ultimate bonding strength with design strength full coral aggregate seawater concrete.(5)Compared with the types of FRP ribs,the parameters of deformed FRP ribs have a greater influence on the ultimate bonding force.BFRP,GFRP bars with relatively large rib inclination angle and rib height have a limit bond with seawater concrete with full coral aggregate,which is greater than CFRP bars with relatively small rib inclination angle and rib height.The effect of sand sticking on the surface of FRP tendon for lifting the ultimate bond load is not obvious.Because when the strength of concrete is high,the shear failure surface occurs at the sticky sand substrate;(6)Stirrup restraint may not improve the seawater bonding performance between FRP bars and full coral aggregates,which contradicts the expression of ACI Committee 440.With the same concrete strength,the ultimate bond between BFRP bars and full coral aggregates is higher than that of ordinary seawater concrete.This is because the coral reef sand has a large water absorption rate,and its water purification ash is relatively small,resulting in higher cement mortar strength;(7)The mechanism of the bond failure mode between BFRP bars and full-coral aggregate seawater concrete lies in the anti-split ability of BFRP ribs and inter-rib concrete,and the anti-split ability of concrete.The specimen with a smaller diameter and a shorter bonding length has a greater ultimate bond strength than a specimen with a larger diameter and a longer bonding length.This is because the longer the bonding length,the more unevenly the bonding stress is distributed along the bonding section of the BFRP tendon,and the concrete has a better grip on the smaller diameter BFRP tendons.(8)The larger the relative protective layer thickness,the higher the ultimate bonding stress.Double the relative thickness of the protective layer can increase the ultimate bond strength by 18%-40%.The stirrup restraint improves the anti-splitting ability of the coral concrete,thus bringing about an increase in the cohesive strength and an increase in the ultimate cohesive strength by 10%-24%.(9)A bond-slip constitutive model of FRP tendons and full-coral aggregate seawater concrete was established and model parameters were solved.The results showed that the model curve and the test curve accord with each other to a high degree.Finally,the basic anchoring length was derived.The paper contains 124 figures,26 tables,and 136 references.