Study On Bond-slip Constitutive Models Of Recycled Concrete

In response to the national sustainable development strategy and saving natural ore resources,recycled concrete,as a new building material,emerges as the times require in the civil engineering industry.The premise of the coordination of rebar and concrete is that they have excellent bonding properties.Studying the bond-slip performance and establishing bond-slip constitutive model between rebar and concrete can provide an important theoretical basis for the design of reinforced concrete structures.At present,there are abundant research results on ordinary concrete at home and abroad as far as the bond-slip constitutive model of concrete is concerned,while the research results of recycled concrete are relatively scarce.Therefore,it is of great significance to study the bond performance and establish the bond-slip model of recycled concrete to improve the design code of recycled concrete.Through the central pull-out test,the research group studied the influencing factors of recycled concrete bond performance,and carried out a theoretical study on the bond-slip constitutive model of recycled concrete.The main conclusions are as follows:(1)Through the central pull-out test,a total of 40 groups of specimens were made to explore four factors,namely,replacement ratio of recycled coarse aggregate(RCA)(0,30%,50%,75%,100%),addition ratio of steel fiber(0,0.35%,0.8%,1.5%),strength grade(C20,C40,C60)and loading rate(0.1 k N s,1 k N s,2k N s,5 k N s),on the failure modes and bond-slip performance of recycled concrete.(2)Based on the analysis of the experimental phenomena,the central pull-out specimens are divided into 3 types of failure modes: split failure,split pull-out failure and pull-out failure.C60 concrete specimens without steel fiber mainly suffered splitting failure,and the bond-slip curves were incomplete;C60 concrete specimens with steel fiber addition ratios of 0.35% and 0.8% and all C40 and C20 recycled concrete specimens suffered split pull-out failure;C60 concrete specimens with a steel fiber addition ratio of 1.5% suffered pull-out failure.(3)Based on the test results,the influence of four factors on the bond-slip performance of recycled concrete is analyzed.With the increase of replacement ratio of RCA,the ultimate bond strength and ultimate slip of specimens decreases;Adding steel fiber can obviously improve its bond-slip performance,among which the ultimate bond strength,ultimate slip and residual strength are the largest when the steel fiber addition ratio is 0.8%;With the increase of strength grade,the bond strength of specimens increases,and the slope of bond-slip curve increases obviously;With the increase of loading rate,the ultimate bond strength of specimens increases,and the corresponding ultimate slip is on the contrary.(4)Through the analysis of test results,the bond-slip constitutive model of recycled concrete is established.Combined with test data,its correctness is verified and the influencing factors of the constitutive model parameters are explored.It is concluded that the parameters of the bond-slip constitutive model established in this paper have a linear relationship with the strength grade and the replacement ratio of RCA.(5)Based on the bond slip constitutive model of recycled concrete,the Spring-2nonlinear spring element is established to simulate the bond slip by using ABAQUS software.The load-displacement curves are compared with the test curves,and the correctness of the constitutive model is further verified.