Proportion Design And Performance Test Of Steel Fiber Reinforced Concrete In Anchorage Area Of Bridge Expansion Joint

The concrete in the anchorage zone of bridge expansion joint is vulnerable due to vehicle impact and fatigue load.Steel fiber can significantly improve its impact resistance and fatigue resistance.This paper is based on the science and technology project "Application Research of high toughness concrete in bridge expansion joint" entrusted by Beijing Municipal Fourth Construction Engineering Co,Ltd.The mix ratio of steel fiber reinforced concrete(SFRC)was optimized with different targets and the difference of impact resistance and fatigue resistance among them was compared.The main contents and conclusions of this paper are as follows:(1)SFRC is prepared according to the engineering requirements,and compared with ordinary concrete,the results show that the "scaffolding" effect formed by steel fiber in concrete mixture will lead to the decrease of slump and increase of expansion.The results show that steel fiber can increase the concrete proportion limit by 18.8%,the ductility coefficient by 8.4%,the flexural strength by 18%,the fracture energy by 8.5 times,and the deformation resistance and flexural toughness of concrete are obviously improved,but the compressive strength has no significant change.(2)This paper analyzes the main factors affecting the physical and mechanical properties of SFRC,studies the influence of each factor and its significance level through orthogonal test,establishes regression equation,optimizes with two different objectives,and compares the performance differences.The results show that the performance of SFRC has different trends with the changes of sand ratio,aggregate cement ratio,steel fiber content and length,and the aggregate cement ratio and sand cement ratio are different The influence of steel fiber ratio on the workability of concrete is more significant,and the influence of steel fiber parameters on the mechanical properties of concrete is more significant.The compressive strength,proportional limit,ductility coefficient and fracture energy of SFRC obtained by the efficiency coefficient method are increased by 14.8%,13.3%,3.4% and 30% respectively.The flexural strength is also slightly increased.The load decline speed after the peak load is slowed down.The plastic failure characteristics of concrete are further eased.The deformation resistance and bending toughness of SFRC are improved Although the compressive strength and proportion limit of concrete increase by 28% and 33.4%,the ductility coefficient,flexural strength and fracture energy of concrete decrease by 5.2%,2.6% and 41% respectively.The plastic failure of concrete is intensified,and the deformation resistance and bending toughness are insufficient.(3)Through the research on the impact resistance of SFRC,it is found that:steel fiber can avoid the phenomenon of concrete cracking under the impact load,improve the brittle failure characteristics,and increase the impact energy consumption by more than 2.4 times.The impact energy consumption,ductility ratio and toughness coefficient of SFRC obtained by the efficiency coefficient method are increased by 6.7% and 3.0% respectively,The impact energy consumption of SFRC with the highest compressive strength has no significant change,but the impact ductility ratio and toughness coefficient decrease by 15.2% and 3.9%,and the impact resistance is poor.(4)The results show that the peak load of concrete decreases and the corresponding strain increases.At the initial stage of loading,there is no obvious degradation of concrete performance.With the increase of loading times,the degradation phenomenon intensifies,and brittle failure occurs after reaching the peak value.Steel fiber can reduce the average growth rate of plastic strain of concrete by 10.8%,and increase the residual stress.The growth rate of plastic strain and residual deflection of SFRC obtained by efficiency coefficient method is slowed down by 7.9% and 1.6%,and the slope of compression and bending curves is slowed down by 8% and 8.6%.While the plastic strain and residual deflection of SFRC obtained by compressive strength method are reduced by 2.9% and 4.8%,but the bending resistance of SFRC is improved The slope of the curve decreased by 4.9%.(5)Aiming at the failure of concrete in anchorage zone at the early stage of service,the performance changes of concrete after a certain number of fatigue loads with different stress levels are studied.The results show that:after a certain number of fatigue loads are applied,there is no significant crack on the surface of concrete block.With the increase of stress level,the peak load decreases and the corresponding strain increases,The results show that the ratio limit,deflection,flexural peak load and fracture energy of SFRC are-8%,20%,-7% and-8%respectively by the efficiency coefficient method,while the variation range of SFRC with the maximum compressive strength is-22%,17%,-12% and-20%.The ductility coefficient of each concrete has no significant difference,but the ductility coefficient of SFRC optimized by the efficiency coefficient method is also the same With higher coefficient,its deformation resistance and flexural toughness are obviously better than other concrete,and it has better fatigue resistance.