Research On Coastal Concrete Structures Strengthened With CFRP

It have been confirmed by site investigations for many years past that crack or evendelamination of cover due to rebars corrosion in reinforced concrete structures is a mainreason resulting in rebars exposing completely to external environment, and reduce thestructures durability to an unacceptable level. And carbon fiber reinforcement polymer(CFRP) is largely applied for structures rehabilitating around world including China becauseof extraordinary properties, especially its tension and durability properties. Hence, thefollowing research works are developed based on the project Research on technology systemof coastal concrete structures strengthened with CFRP which launched and supported byCHEC:1. Moisture-curable adhesives applicable for bonding CFRP on moisture concrete surfaceare developed, and materials strength, bond strength or technical properties meet all therequirements given by the nation's specification. In order to confirm extensive applicability ofthe adhesives, further testing researches are performed on bond strength when the adhesivesapplied to saturate carbon fiber and then bond on moisture concrete surface, and comparing tothat when Araodite adhesives, a kind of marketable, are applied. Furthermore, applicabilityof the moisture adhesives have also been confirmed through bending test of reinforcedconcrete beams strengthened with CFRP, and it can be observed that the performance of thebeams bonded by the moisture adhesives seems not worse than those bonded by Araoditeadhesives.2. Short-term and long-term mechanical properties of CFRP are researched throughlaboratory test and the specimens for long-term have been experienced immersing in alkalisolution, salt solution or laboratory fast aging respectively before tension test. The aboveenvironment factors have almost no effect on ultimate strength of CFRP, however, can reduceultimate elongation obviously,while can increase modulus. The relationship betweenσandεof CFRP is elastic and linear as per test results, and the conclusion can be applied in analyzingCFRP strengthened structures.3. It is observed that Cl~- can be prevented effectively from immigrating into concrete whenconcrete surface bonded with CFRP through laboratory test. Therefore, besides asreinforcement when coastal concrete structures are repaired and strengthened, CFRP bondedon surface of concrete can be regarded as a part of corrosion protection system on concretesurface. 4. There are 24 beams experienced loading test for bending performance of reinforcedconcrete beams strengthened with CFRP. The results indicate that bending capacity andstiffness of reinforced concrete beams may increase, and crack may be controlled afterreinforcing by bonding CFRP externally. Much CFRP is applied, the above effects seemsmuch obviously. CFRP play a higher role on increasing beams performance after crack thanbefore, and the function gradually reduce as content of rebars increased. Normally, the failuremode of reinforced concrete won't change after being reinforced with CFRP forbending. Analysis on testing data indicate that there are an acceptable difference betweentesting value and calculation value which based on formula in the nation's specification, andthe formula can be introduced into CFRP strengthening coastal concrete structures.5. There are 4 reinforced concrete plates experienced loading test for bending performanceof reinforced concrete plates strengthened with CFRP. Similarly to reinforced concrete beamsstrengthened with CFRP, bending capacity and stiffness of reinforced concrete plates mayalso increase, and crack may be controlled after reinforcing by bonding CFRP externally. Thefailure mode are caused by bending. In addition, analysis on testing data indicate that testingvalues is lower than calculation values which based on formula in the nation'sspecification. Thus, a reduction factor will be introduced into calculation system for CFRPstrengthening coastal concrete structures.6. There are 28 beams experienced loading test for shear performance of reinforced concretebeams strengthened with CFRP. Besides reference beams, there are still some beamsexperienced fast corrosion or pe-load to crack before bonding CRRP. The results indicatethat there is almost no effect of damage due to corrosion or pre-load on performance ofreinforced concrete beams strengthened with CFRP. In addition, the load-deflection curve isformed by two beelines for those experienced corrosion or pe-load. Shear capacity can beobviously increased and keep well ductility when completely wrapped CFRP scheme isapplied for shear strengthening, while there is very small different performance between3-sided "U-wrap" and 2-sided wrap, and the failure is brittle. Analysis on testing dataindicate that testing values is lower than calculation values which based on formula in thenation's specification. Thus, a reduction factor will be introduced into calculation system forCFRP strengthening coastal concrete structures.7. There are 18 square-section plain concrete columns, 12 circle-section plain concretecolumns, 12 square-section reinforced concrete columns respectively experienced loading testfor axial compression performance of column wrapped with CFRP. The test results indicate that axial compression capacity of plain concrete columns increase largely when wrappedwith CFRP. Much more area wrapped with CFRP, much higher capacity of plain concretecolumns are. The maximum increment of axial compression capacity is 36% whensquare-section plain concrete columns are completely wrapped with CFRP. Althoughwrapping CFRP can also increase axial compression capacity of square-section reinforcedconcrete columns, the increment seems much smaller than that of plain concrete columns.