Experimental Study On Flexural Behavior Of Reinforced Concrete Beams Repaired With ECC

Engineered Cementitious Composites(ECC)has attracted the attention of scholars at home and abroad for its ultra-high toughness and crack control characteristics since it was proposed.With the in-depth study of the basic mechanical properties of ECC materials,some scholars began to consider the use of ECC as an external material for the repair of reinforced concrete structures.However,the current research on ECC repair of reinforced concrete structures mostly focuses on improving the bearing capacity of the repaired structures,and the research on crack performance of the repaired structures in the normal service stage is not perfect.Based on four-point bending tests of 10 ECC repaired beams and 1 RC beam,the effects of experimental variables such as volume fraction of PVA fibers in ECC layer,thickness of ECC repaired layer and damage parameters of existing reinforced concrete beams on flexural properties of repaired beams are analyzed,and the crack calculation model and flexural capacity calculation formula of ECC repaired beams in service stage are established.The main contents and achievements of this paper are as follows:Based on the bending test of ECC repairing existing RC beams,the failure modes,load-deflection curves and the strain and characteristic loads of reinforcement and concrete of the test beams are studied and analyzed.The results show that the stiffness of ECC repairing beams is improved to varying degrees compared with RC beams,and the deformation lags behind that of the contrast beams.The crack properties of the repaired beams are improved,the crack spacing and width of the repaired beams are smaller than those of the comparative beams,and the crack morphology is more compact,and the larger the fiber content in the ECC layer of the repaired layer,the more significant the improvement of the cracks;the thicker the repaired layer,the finer the vertical cracks of the repaired beams in the pure bend section;the larger the damage parameters,the more disadvantageous the improvement effect of the repaired beams cracks.?According to the analysis of the test results,With the increase of PVA fiber content in ECC of repairing layer,the characteristic load of repairing beam increases remarkably,and the effect on cracking load is most obvious;the effect of repairing layer thickness on bearing capacity is not positively correlated;when the thickness of ECC layer is too large,the ECC layer fails prematurely and the increase of bearing capacity begins to decrease due to the inconsistency of interface deformation;the damage parameters also have a certain degree of influence on the characteristic load of repairing beam.The larger the damage parameters are,the smaller the increase of the characteristic load of the repaired beam will be,and the impact of the damage parameters on the yield load of the repaired beam will have a greater impact on the ultimate load.Based on the crack calculation theory of ordinary reinforced concrete beams in normal service stage and considering the crack control characteristics of ECC layer,the effects of experimental variables such as PVA fiber content in ECC repair layer,thickness of ECC repair layer and damage parameters of existing reinforced concrete beams on cracks in pure bend section of repair beams are analyzed,and a crack calculation model of ECC repair of existing reinforced concrete beams is established,which can be compared with each other.The spacing and width of cracks can be well predicted,and a simplified formula for calculating the flexural capacity of ECC repaired existing reinforced concrete beams is established based on the assumption of section and the effect of test parameters on the stress of repaired beams.The calculated results are in good agreement with the experimental data,which can be used as a reference for engineering design.