Study On Bond Behaviour Between GFRP Bars And Recycled Aggregate Concrete

Since the 21 st century,a very large quantit ies of construct ion and demolit ion waste are produced because lots of old buildings have been demolished,how to deal with abandoned concrete and other materials has become a serious problem.On the other hand,rebar corrosion causes c racking and spalling of concrete,which reduces the bearing capacit y of the structure.From the two aspects above,considering green environmental protection o f recycled aggregate concrete and corrosion resistance,light and other characterist ics of GFRP(Glass Fibre Reinforced Polymer)bars,in this paper,the component between GFRP bars and recycled aggregate concrete is proposed,and the possibilit y of using it in practical engineering is studied.As to GFRP bars and recycled aggregate concrete,good bond behaviour between GFRP bars and concrete is the base of structure to work together,and is the key factor to ensure the qualit y of concrete structure.The basic physical properties of natural aggregate and recycled aggregate were tested,including gradation,apparent density,bulk densit y,water absorption,crushing index.Three different concrete grades(i.e.C20,C30,C50)were prepared,each containing four mixes,where the recycled aggregate concret e were used at rates of 0%,25%,50% and 100% of the recycled aggregate total weight.The 78 cubic specimens were used to determine compressive strength at 7 days and 28 days and the 36 cubic specimens were used to determine tensile splitt ing strength at 28 days.Then 96 GFRP bars and recycled aggregate concrete specimens of the 150 mm×150 mm×150 mm same size were designed,considering the fators of surface treat ment of GFRP,concrete grades,recycled concrete aggregate replacement ratio in this paper,to co nduct pull-out tests.Based on the experiment,the bond-slip and failure mode were studied,the mechanism and influence on bond strength were discussed,the variat ion law of the ult imate bond strength and other basic variables in the process of bond-slip were analyzed.The experiment results show that the ultimate bond strength between GFRP bars and recycled aggregate concrete decreases nonlinearly with the increase of replacement ratio of recycled aggregate;The decrease rate of the lowest concrete grade ca tegory(i.e.C20)is higher than that of the medium concrete grade category(i.e.C30)and highest concrete grade category(i.e.C50),which the highest decrease rate in grade C20 is 37.6%.The ult imate bond strength between GFRP bars and recycled aggregat e concrete decreases with the increase of the diameter of the bars.According to separate finite element model in ABAQUS,a three-dimensional finite element model between GFRP bars and recycled aggregate concrete is established,and spring elements were used to complete nonlinear numerical simulat ion.The basic variables in the process were obtained and compared with the experimental results in this paper.It can be concluded that the model established in this paper can accurately simulate the actual bond behavior and basic bond-slip variables between GFRP bars and recycled aggregate concrete.The distribut ion of the bond stress along the anchor lengt h direct ion between GFRP bars and recycled aggregate concrete is very uneven,and the stress value increases gradually from the free end to the loading end.Based on the test results in this paper and formerworks,a new equat ion for anchor length and design recommendat ions of concrete protective layer are proposed,considering the fators of diameter of GFRP,concrete grades,recycled concrete aggregate replacement ratio,which provides the references for the compilation of relevant design codes.After comparing test results and several bond-slip const itut ive models,it can be found that test results in this pa per are coincident with continuous curve model,and the free end is better fitted than the loaded end.Compare with the ascending branch,the descending branch agrees well with the theoret ical model,then the cont inuous curve model is revised.