Flexural Behaviour Of Steel Fiber-Reinforced Recycled Aggregate Concrete Beams Reinforced With BFRP Rebars

The technology of recycled concrete can reuse waste concrete and contribute to the sustainable development of society and the natural environment,which has draw growing attention of scholars.In addition,in view of some shortcomings of recycled concrete itself,some researchs further proposed to improve the performance by adding fibers into the recycled concrete.And they found that the right amount of steel fiber has better strengthening and toughening effect on recycled concrete,which can meet the needs of engineering applications.On the other hand,basalt fiber reinforced polymer bars(BFRP bars),as a new type of FRP bars,have the characteristics of light weight,high strength,good corrosion resistance and non-magnetic properties,which can effectively avoid to shortening working years of concrete members due to steel corrosion and reduce the structural weight.Therefore,based on the huge potential engineering application value and for the preparation of relevant specifications provides data reference and support,it is hoped that through the testing and theoretically studying on the bending behavior of BFRP bars-steel fiber reinforced recycled concrete beams can provide data reference and support for the future application of this type of component in engineering practice and the compilation of relevant specificationsThe simple bending test of 9 BFRP bars reinforced recycled concrete beams and 1 steel bars reinforced recycled concrete beam is was firstly carried out.The influence in bending resistance with different reinforcement ratio,replacement ratio of recycled aggregate and types of reinforcement were studied.The bending mechanical properties of BFRP bars reinforced recycled concrete beams and the feasibility of engineering application were verified.The results show that the replacement ratio of recycled aggregate has slight effect on the flexural behavior of BFRP bars reinforced recycled concrete beams,while the reinforcement ratio has a greater impact.Due to the low elastic modulus and high strength,there has a poor cracking performance,wider cracks and larger deformation before failure of the BFRP bars reinforced recycled concrete beams.It is suggested that the BFRP bars reinforced recycled concrete beams should be designed as over-reinforced beams.Secondly,based on the experimental research above,11 BFRP bars-steel fiber reinforced recycled concrete beams and 1 steel bars-steel fiber reinforced recycled concrete beam were designed.The effects of different steel fiber volume fraction,depth of steel fiber reinforced concrete layer,replacement ratio of recycled aggregate,reinforcement ratio and reinforcement types on the flexural capacity were studied by three-point bending test.The differences in failure modes,characteristic loads,concrete and longitudinal reinforcement strain,mid-span deflection,crack development and ductility of the test beams were analyzed and compared.The results show that the steel fiber significantly improves the characteristics of recycled concrete and improves the flexural capacity and cracking performance of the test beam.The use of steel fiber reinforced concrete in the tension zone is beneficial to improve the flexural performance of the beam.Although the ultimate bearing capacity is reduced,the partially fiber-reinforced components are obviously better than no-fiber reinforced specimens in terms of cracking performance and bearing capacity,when compared with the full-section steel fiber reinforced recycled concrete component.Finally,based on the current domestic and international design codes and relevant theory,the crack width and deformation of BFRP-steel fiber reinforced recycled concrete beams were checked.The calculation results were compared with the experimental data to estimate whether the guidelines are adequate for the BFRP bars reinforced recycled concrete beams,and relevant suggestions were given.In addition,the calculation formula of ultimate bearing capacity of BFRP-steel fiber recycled concrete beam was proposed considering contribution of steel fiber in the tension zone to the flexural capacity.It is suggested that the calculation result is more accurate as the ultimate pressure strain of steel fiber recycled concrete is 0.0035~0.004.