Experimental Study On Flexural Fatigue Behavior Of PVA-ECC Reinforced Beam With Salt And Frost Cycles

Compared with ordinary concrete material,PVA-ECC material has good crack control ability,high toughness and strong deformation ability.It has great research significance and practical value for the durability of the structure.Combined with the severe damage of frost damage to concrete bridge structure in cold area of our country,and the great development of high performance concrete.And good application prospect.It is of practical significance to study the durability of PVA-ECC material.In this paper,the component of PVA-ECC reinforced beam is taken as the research specimen.Experimental study on fatigue behavior of PVA-ECC reinforced beams after chloride and freeze-thaw cycles.The main work of this paper is as follows:(1)Freeze-thaw cycle test of PVA-ECC reinforced beam under chloride environment,study the specimens before and after freeze-thaw damage appearance development,mass loss,the loss of relative dynamic elastic modulus,and microstructure analysis of salt freezing damage mechanism.The experimental results show that: the freezing resistance of the specimens with fiber volume fraction of 2% and 1% is close,and the frost resistance of the specimens is far more than that of the non doped specimens.(2)In order to provide the theoretical basis for the subsequent fatigue test,the bending static load test of PVA-ECC reinforced beams was carried out.The development of crack number,width and height are analyzed,and the load-deflection curves of the specimens under different factors(fiber volume fraction and the number of freeze-thaw cycles)are analyzed.The results show that: freeze-thaw cycle can reduce the bearing capacity of the test beam.After 300 cycles of freeze-thaw,the reduction of bearing capacity is not obvious.The load-deflection curve into two stages of development,The incorporation of fiber can improve the bearing capacity and stiffness of the beam.The more the number of freeze-thaw cycles,the first entry of the beam into the yield stage.After freezing and thawing of the beam into the yield stage,the flexural toughness decreases obviously,and the beam quickly destroyed.(3)The fatigue test of PVA-ECC reinforced beam was carried out,and the fatigue failure mode and crack development were analyzed.The fatigue deflection-cycle number curve and fatigue residual deflection-cycle number curves of the test beams were analyzed.Based on the relationship between the stress level and the number of fatigue cycles,theS-N curve equation was established to fit the experimental data.The results show that: the maximum load deflection and residual deflection of the test beams are similar to those of the fatigue cycles,which can be divided into three stages.The higher the stress level or the more the number of freeze-thaw cycles will lead to the increase of the maximum bending deflection and residual deflection of the test beam,the shorter the fatigue life.The maximum fatigue strain and residual strain of PVA-ECC beam are also considered as the three stage model.The law of strain development reflects the change of damage in the test beam.With the increase of freeze-thaw cycles,the internal defects of the test beams increase,which results in the increase of strain.The increase of fatigue stress accelerated the internal damage of the test beam,which showed that the strain increased.