| Due to the poor tensile performance of concrete,cracks usually appear at the negative bending moment of reinforced concrete(RC)continuous beam bridges.The structure with cracks is more subjected to Chloride ion erosion.Engineered cementitious composites(ECC)is widely used in the construction field due to its excellent tensile property.The paper used ECC to substitute ordinary concrete in the zone bore the negative bending moment,considering the stress characteristics and actual diseases of the precast concrete continuous girder bridge.Based on the coupling of chloride salt dry wet cyclic erosion and negative moment bearing capacity,the mechanical performance of ECC in the negative moment zone of RC continuous beam bridges was studied via model tests and theoretical analysis.The ECC-RC composite continuous beams(hereinafter referred to as ECC beams)casted in the middle of RC concrete were designed and manufactured.Meanwhile,two RC concrete beams were used as control groups.Wet-dry cycles were performed every 7 days(4 days of wetting and 3 days of drying).The variables were 25 times,40 times,70 times of wet-dry cycles and 30 %,50 %,70 % Pu loading.The main conclusions were as follows:(1)The long-term deterioration test of ECC beams under the coupling effect of salt intrusion and sustained load was carried out,and the cracking behavior of the test beams and steel corrosion rate of the test beams were studied.The results showed that the crack width of ECC beam was smaller than that of RC beam in salt intrusion stage.The beam with the smallest long-term load had the smallest crack width and the lowest corrosion rate.The corrosion rate of steel bars gradually increased with time.The bending test of the deteriorated beam was carried out to observe and record the crack development and failure mode of the test beam in the bending test.The failure mode of ECC beam was that a small amount of ECC in the compression zone is crushed,and then the tensile steel bar is broken.For ECC,multi-cracks cracking occurred during the bending test.In the bending test,the crack width of ECC beam was much thinner than that of RC beam under the same load.(2)The deformation performance of the test beam under the coupling effect of salt intrusion and load was analyzed.The deflection growth of ECC beams under salt intrusion was thinner than that of RC beams.The deflection growth of beams increased with the increase in loading.The load-deflection curve of the test beam during the bending test was studied.The results showed that the ultimate deflection of ECC beam decreased after salt intrusion.The ductility of specimens with long loading time and large loading grade decreased more seriously.After salt intrusion,the stiffness of the test beam increased while the porosity of ECC decreases causing the increase in stiffness.The porosity was the lowest when Wet-dry cycles reached 40.(3)The ultimate bearing capacity of the deteriorated ECC beam was studied.The ultimate bearing capacity of the test beam decreased after salt intrusion,and the load loss rate of ECC beam was less than that of RC beam.The decrease in bearing capacity of the test beam was proportional to the long-term load level.The ultimate bearing capacity of ECC beams with small load level slightly changed with time.The corrosion of steel bars would cause the decrease in ultimate bearing capacity of ECC beams,and the more corrosion of steel bar,the more decreased in the bearing capacity of the beams.ECC beam had a better resistance to salt intrusion than RC.ECC and steel bar possessed well compatibility of deformation.(4)The bearing capacity degradation model of the test beam under the coupling of salt intrusion and sustained load was established,and the calculated data was in consistent with the experimental data.When calculating the bearing capacity of ECC,it should consider the tensile effect of ECC.For ECC-RC beams,the relative bearing capacity of ECC and concrete sections should be calculated,and the minimum value was adopted. |
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