Experimental Study On Shearing Behavior Of Steel Fiber-reinforced Concrete With Recycled Aggregates Beam Without Stirrups

The construction industry is a traditional high-pollution,high-energy and labor-intensive industry.Under the strategic background of national industrial upgrading,it has become an inevitable trend to realize green sustainable development of construction industry.The recycled aggregates with different particle sizes were prepared by crushing of waste concrete,which partially or totally replaced natural aggregates for engineering construction.This approach can alleviate the overexploitation of natural resources and realize the resource utilization of construction waste.Milled steel fibers are added into recycled aggregate concrete as aggregate to prepare steel fiber-reinforced concrete with recycled aggregates,which can make up for the defects of crack resistance and durability of recycled aggregate concrete.Therefore,it is necessary to research the mechanical properties of ssteel fiber-reinforced concrete beam with recycled aggregates.In this paper,10 steel fiber-reinforced concrete with recycled aggregates beam without stirrups are designed and manufactured.Under the condition of the same concrete strength,shear span ratio and section size,it takes the volume ratio of steel fibers as the experimental variable,and the volume ratio of steel fibers influences the shear performance of steel fiber-reinforced concrete with recycled aggregates beam without stirrups.It summarizes the specimens with steel fiber volume fractions of 0%,0.8%,1.2%,1.6%and 20%respectively,including crack development,failure mode,deflection,initial crack load and the growth law of ultimate load.At the same time,the formulas of shear capacity of steel fiber-reinforced concrete with recycled aggregates beam without stirrups proposed by current concrete codes at home and abroad and other scholars are checked with test data,and the correlation between the formulas and the measured data of steel fiber-reinforced concrete with recycled aggregates beam without stirrups is tested.The specific conclusions are as follows:1.The failure modes of steel fiber-reinforced concrete with recycled aggregates beam and recycled aggregate concrete beams are the same,both of which are shear-compression failure.The volume ratio of steel fiber has no effect on the failure types of specimens.2.The existence of steel fibers can improve the cracking load of recycled aggregate concrete beams without stirrups.When the volume ratio of steel fiber is 0.8%,1.2%,1.6%,and 2.0%,the cracking load of steel fiber-reinforced concrete with recycled aggregates beam without stirrups is 10%,11.43%,24.29%and 20%higher than that of recycled aggregate concrete beams without stirrups.3.After the main oblique cracks suddenly appear in some beams without stirrups,the internal stress will be redistributed to reach a new internal force equilibrium state.When the internal force of the beam without stirrups is balanced,the ultimate load of the test beam will be higher than that of the main oblique crack.The main oblique cracks of some beams without stirrups do not form a new internal force balance state,and then they will be destroyed rapidly after the main oblique cracks occur.4.The strain law of longitudinal reinforcement of steel fiber reinforced recycled aggregate concrete beams without stirrups is very similar to that of recycled aggregate concrete beams without stirrups.At the beginning of the strain period of longitudinal reinforcement in the shear span region,it develops slowly.When there are oblique cracks in the shear span region,the strain of longitudinal reinforcement in the corresponding position accelerates obviously.When there are main oblique cracks in the shear span region,the strain of longitudinal reinforcement in the corresponding position changes abruptly.5.Steel fiber can increase the deflection of steel fiber-reinforced concrete with recycled aggregates beam without stirrups and make the specimens have better ductility.