Study On Bond Durability Of FRP Bars Embedded In ASSC Under Coupling Effect Of Seawater Immersion And Sustained Loading

How to help China achieve the "double carbon goal" in the construction industry is a hot research topic nowadays.The use of corrosion-resistant fiber reinforced plastic（FRP）reinforcement instead of steel as a reinforcing material,combined with non-cement-based alkali-excited seawater sand aggregates concrete（ASSC）,the development of highperformance FRP reinforced ASSC（FRP-ASSC）new marine engineering structures,not only can reduce carbon emissions from the production of steel and cement,the effective use of industrial waste and abundant seawater sand resources.It can also solve the bottleneck problem of corrosion of steel reinforcement directly applied in seawater sea sand concrete,which has important scientific significance and engineering value to promote the sustainable development of China’s construction industry.It is worth pointing out that in the FRP-ASSC composite flexural members,the FRP reinforcement-ASSC interface is an important part to realize the reinforcing effect of FRP reinforcement,and the force transfer and deformation coordination of the flexural members are carried out through the bonding effect of FRP reinforcement and ASSC.Therefore,the study on the bonding performance of FRP reinforcement and ASSC interface can help to correctly evaluate the mechanical properties of FRP reinforced ASSC structure and its service life.However,so far,scholars at home and abroad have focused on the study of short-term mechanical properties of FRP reinforcement and ordinary concrete interface,and the study of long-term performance of FRP reinforcement bonded to geopolymer concrete interface is quite limited,and no research on the evolution law and deterioration mechanism of FRP reinforcement-ASSC interface bond performance under seawater environment has been reported.To this end,this study takes ASSC and FRP reinforcement-ASC interface as the research object,and adopts a combination of experimental-based and theoretical analysis from the material level to the member level to explore the synergistic working mechanism of FRP reinforcement and ASSC under seawater immersion environment,reveal the deterioration mechanism of FRP reinforcement-ASC bond interface under environmental and load coupling,and investigate the bond performance of the interface.And compare the existing bond-slip instantiation models of FRP reinforcement-ASSC interface.The main research work and conclusions of this paper are as follows.（1）The alkali-excited seawater-sea sand geopolymer concrete（ASSC）was developed by mixing seawater and sea sand with fly ash and slag as cementitious materials and sodium hydroxide（Na OH）and sodium silicate（Na2Si O3）solutions as alkali excitants,and the fly ash-slag dosage ratios（3:7,5:5,7:3）and alkali modulus（0.8,1,1.25,1.5）were used as variables to study the The setting time,slump,compressive properties of the above variables ASSC,combined with SEM scanning electron microscope test to analyze the damage mechanism study results show that: the increase of slag dosage will significantly reduce the slump,shorten the setting time,and significantly increase the compressive strength;the increase of alkali modulus in the range of 0.8 to 1.5 does not affect the slump,but can prolong the setting time and reduce the compressive strength;SEM electron microscope scan can It is found that the geopolymer matrix of ASSC is more dense with the increase of slag content,while the denseness of the matrix decreases with the increase of alkali modulus.（2）Prepared ASSC cylinders for axial compression tests to study the effects of fly ashslag dosage ratio（3:7,5:5,7:3）,alkali modulus（0.8,1,1.25,1.5）and seawater immersion time（60,180 days）on the mechanical properties of ASSC such as elastic modulus,Poisson’s ratio,and toughness.The results show that: the elastic modulus and toughness increase significantly with the increase of slag dosage,but there is no significant effect on Poisson’s ratio;the increase of alkali modulus in the range of 0.8～1.5 will reduce the elastic modulus and toughness;there is no significant change in the elastic modulus and Poisson’s ratio with the increase of seawater soaking time,and the toughness decreases with the increase of soaking time.The stress-strain curve of cylindrical axial compression obtained from the axial compression performance test was compared with the existing stress-strain curve model,and the test stress-strain curve fitted well with the concrete stress-strain curve model given by GB/T 50010-2010.（3）The FRP reinforcement concrete interfacial bond performance central pullout test specimens were prepared,considering the concrete type（ANNC,ASSC）,FRP reinforcement fiber type（GFRP reinforcement,BFRP reinforcement,CFRP reinforcement）,corrosion age（0,60,180 days）and corrosion conditions（seawater immersion effect,seawater and load coupling effect）on the FRP reinforcement ASSC interfacial bond performance.The results show that the type of concrete has a small effect on the interfacial bond strength of FRP reinforced concrete;the type of FRP reinforcement has a significant effect on the interfacial bond strength,and the interfacial bond strength of CFRP reinforcement and ASSC is the highest,followed by BFRP reinforcement and GFRP reinforcement.The interfacial bond strength of CFRP reinforcement and ASSC was the highest,followed by BFRP reinforcement,and the lowest by GFRP reinforcement;with the increase of corrosion time,the interfacial bond strength of FRP reinforcement ASSC showed a trend of increasing and then decreasing;the interfacial bond strength of FRP reinforcement ASSC under the action of seawater and load coupling was always lower than that of FRP reinforcement ASSC under the action of seawater immersion;SEM electron microscope scan found that the resin matrix of FRP reinforcement with the corrosion time The degradation of the FRP rib ASSC interfacial bond strength is mainly due to the degradation of the FRP rib due to the hydrolysis of the FRP rib resin matrix and the fracture of the fibers,which reduces the interfacial bond strength.（4）Based on the prediction method proposed by CEB-FIB,the long-term bonding performance of the interface between FRP rib and ASSC was predicted,and the predicted results showed that the retention rate of the interfacial bond strength of GFRP rib ASSC under the action of seawater immersion and seawater load coupling were 49.22% and 33.03% at 50 years,and the retention rate of the interfacial bond strength of BFRP rib ASSC were 54.84%and 41.84% at 50 years,respectively.The retention rates were 54.84% and 41.65% for BFRP bars,and 68.27% and 60.95% for CFRP bars at 50 years,respectively,and the retention rate of ASSC interfacial bond strength of FRP bars stabilized after 50 years of exposure.Comparison of the tested ASSC axial compression bond-slip curves with existing models as well as the analysis revealed that the bond-slip curves obtained from the tests in this study fit better with the Malvar model.