Performance And Calculation Method Of Steel Fiber Reinforced Recycled Aggregate Concrete

With the deep devolpment of infrastructure construction,demolition,maintenance and reinforcement of existing buildings,more and more demolition waste concrete were produced.Recycling waste concrete into recycled aggregate is an effective method to realize sustainable development.Recycled aggregate concrete(RAC)is regarded as inferior to natural aggregate concrete in terms of its structural properties,and mainly used in non-loadbearing structures such as subgrade and pavement pavement.In order to promote recycled concrete application in load-bearing structural,steel fiber is added into recycled aggregate concrete to make the steel fiber reinforced recycled aggregate concrete(SFRAC),the RAC structural properties can be improved by the strengthening and toughening effect of steel fiber,and SFRAC is a structurally sound material.Supported by the key project of National Natural Science Foundation of China(the structure calculation theory and design method of fiber recycled concrete,No.U1704254),the uniaxial compressive properties of steel fiber reforced recycled concrete,the bond behavior of reinforced and steel fiber reinforced recycled concrete,and the flexural properties of steel fiber reinforced recycled concrete beams are mainly investigated,and the corresponding calculation models are established.The main research contents are as follows:(1)With batching by 15 group mixture proportions,the compression and splitting tensile tests of SFRAC were conducted on 90 cubic specimens of 150mm×150mm×150mm,and compression and elastic modulu tests conducted on 90 prism specimens of 150mm×150mm×300mm.The influence of water content,recycled aggregate replacement ratio and volume ratio of steel fiber on compressive strength,splitting tensile strength and elastic modulu were studied.The calculating formulas for compressive strength,splitting tensile strength and elastic modulu of SFRAC were put forward,the formula expressing the strain-stress relationship of SFRAC under axial compression is suggested,which considers the effect of volume fraction of steel fiber and recycled aggregate replacement ratio.(2)The pull-out tests were conducted on 90 cubic specimens of 150mm×150mm×150mm with batching by 15 group mixture proportions.According to the measured strains,the distribution of bond stress and relative bond slip in bonded segment was obtained under the action of load at each stage.The effects of water content,recycled aggregate replacement ratio and volume ratio of steel fiber on the failure mode,bond stressslip curve,bond strength were investigate.Finally,the bond stress-slip constitutive model reflecting the interaction process of rebar and SFRAC was proposed,which considers the effect of volume fraction of steel fiber and recycled aggregate replacement ratio.(3)The flexural test of 13 SFRAC beams were conducted to investigate the effects of water content,recycled aggregate replacement ratio and volume ratio of steel fiber on the cracking moment,crack propagation,crack width,concrete strains and deflection of midspan section.With consideration of the enhanced effect of steel fibre on the cracked section of beams,the calculation method and formulas for the flexural capacity,cracking moment and crack width of SFRAC beam were proposed.Moreover,by following the current national and international standards,the section stiffness of SFRAC beams was predicted based on the effective moment of inertia method and analytical method.The calculation model and formula of crack width and spacing based on bond stress slip theory were established.