Study On Flexural Behavior Of Self-compacting Recycled Concrete Beams Under Load And Chloride Erosion

Self-compacting recycled concrete has the advantages of recycled concrete and self-compacting concrete.It not only realizes the secondary utilization of construction waste,but also solves the problem of pouring and tamping complex joints in practical construction.It has broad application prospects in bridge structures.In fact,the mechanical properties of bridge structures often need to consider the dual effects of load and chloride erosion.Based on this,this paper relies on the National Natural Science Foundation of China project "Research on flexural performance and design theory of prestressed high performance recycled concrete bridge"(51608331).7 self-compacting recycled concrete beams and 7 ordinary concrete beams are made.The influence of continuous load and chloride corrosion on the flexural performance of self-compacting recycled concrete beams was studied by electrochemical accelerated corrosion test and theoretical analysis.Its main work is as follows:(1)The accelerated corrosion tests of self-compacting recycled concrete beams and ordinary concrete beams under no load and working load were carried out with corrosion time as parameter.The effects of corrosion time and load on longitudinal reinforcement corrosion rate,surface rust expansion crack morphology and width,integrity of concrete protective layer and mid-span deflection of self-compacting recycled concrete beams were studied and compared with ordinary concrete beams under the same conditions.The results show that the increase of the corrosion time will cause the change of the corrosion morphology of the longitudinal reinforcement surface in the pure bending section of the beam.When the corrosion time is 12 days,the bearing corrosion will cause more serious damage to the longitudinal reinforcement in the ordinary concrete beam,and at this time the concrete beam protective layer occurred varying degrees of spalling.The development direction of corrosion expansion cracks on the surface of self-compacting recycled concrete beams under load corrosion is different from that under non-load corrosion.The maximum width of corrosion expansion cracks tends to be stable with the increase of time.When the load is corroded,the self-compacting recycled concrete beams show better deformation ability than ordinary concrete beams.(2)Four-point bending tests were carried out on self-compacting recycled concrete beams and ordinary concrete beams after accelerated corrosion test.The effects of corrosion time and load on cracking load,ultimate bearing capacity,stiffness and ductility of self-compacting recycled concrete beams were studied,and compared with ordinary concrete beams under the same conditions.The results show that the cracking load of self-compacting recycled concrete beam is basically unchanged when the mass loss rate is less than 5.912 %.Common concrete beams under the same conditions are more prone to brittle failure;The stiffness variation of self-compacting recycled concrete beams is different under the conditions of no load corrosion and load corrosion.The self-compacting recycled concrete beam after corrosion has better ductility than ordinary concrete beam under the same conditions.(3)The calculation formula of steel bar mass loss rate under corrosion time and load level is given.On this basis,different calculation models were used to calculate the ultimate bearing capacity and short-term bending stiffness of self-compacting recycled concrete beams,and their applicability was compared.Finally,the cracking moment and curvature ductility were calculated.