Experimental Study On Bond-slip Behavior Between Bar And Recycled Concrete

With the process of China's urbanization accelerating and high-rise buildings generally appearing in recent years,there was a huge growth in the amount of building materials used like sand and stone,to make great pressure on our country's natural resource.Recycled concrete is a kind of new concrete mixed by cement,water and waste aggregate which is picked up from demolished construction concrete.The recycling use of resources like waste aggregate can be realized and it is meaningful to construction waste recycling and disposal,environment protecting and the strategy of sustainable development.Bond strain is an important precondition for bar work together with concrete.In view of its importance and complexity,bond-slip behavior has always been a major focus in the research of concrete.With the continuous popularization and application of recycled concrete technique in construction engineering,the research on bond-slip behavior between bar and recycled concrete is a very important and fundamental project as well.On the foundation of recycled concrete performance research and normal concrete's bond-slip behavior research both domestic and abroad,the bond-slip behavior between bar and recycled concrete was studied by the way of combining experiment and theory analysis.And works which have been completed in this paper are as follows:1.Five sets of central pull-out specimens considering 2 different parameters which are recycled coarse aggregate replacement ratio(30%,50%,70%)and strength of recycled concrete(C20,C40)were made and the central pull-out test were carried out.Results get the bond-slip relationship curve of 5 different kinds of recycled concrete.Overall trend of 5 curves is similar to ordinary concrete's which can be divided into 5 failure stages.2.The rule that bond strain change of recycled concrete with recycled coarse aggregate replacement ratio was analyzed by comparing bond-slip relationship curves of different recycled coarse aggregate replacement ratio specimens.That is,replacement ratio is respectively 30%,50%,70%while concrete's strength grade is C20 and replacement ratio is respectively 30%,50%while concrete's strength grade is C40.When the strength grade of recycled concrete is same,its bonding strength increase with coarse aggregate replacement ratio.3.The rule that bond strain change of recycled concrete with its strength grade was analyzed by comparing bond-slip relationship curve belonging to 4 sets of different concrete's strength grade specimens.That is,recycled concrete's strength grade are C20,C40 while recycled coarse aggregate replacement ratio is 30%and strength grade are C20,C40 while replacement ratio is 50%.When the coarse aggregate replacement ratio of recycled concrete is same,its bonding strength increase with strength grade.4.The initial bond slip elastic modulus E0 and the peak bond slip secant modulus Eu are defined.Its geometrical meaning is the slope of the ascending segment of the bond slip curve.The larger the value of E0/Eu,the higher the bond slip performance.The value of E0/Eu increases as the concrete strength grade increases and the substitution rate increases when the replacement rate of recycled aggregates is less than 70%.5.Taking concrete with strength class C20 as an example,the relationship between the replacement ratio of recycled aggregate and the ultimate bond strength is given.By defining the tension-pressure ratio of recycled concrete---ft/fc,the relationship between tension-pressure ratio and the ultimate bond strength and ultimate bond slip are given.Both relationships have good agreement.6.By referring to relevant papers,the bond-slip constitutive equation of recycled concrete is given and parameter a,b are get by combing to test data.Comparing the experimental value with the calculated value of the model and found that it is in good agreement.