Impact Resistance Of Recycled Aggregate Concrete Reinforced With Steel Fibers

Processing waste concrete into recycled aggregate and using it to partially or completely replace natural aggregate for recycled aggregate concrete(RAC)production,which is beneficial and necessary for saving natural aggregate resources and recycling of building resources.However,due to the defects of recycled aggregate,such as lower apparent density,higher water absorption and lower strength,which result in properties of RAC are deteriorated to a greater extent than that of common concrete.Existing studies shown that the incorporation of a suitable amount of steel fibers into the RAC may inhibit the crack development and change the path of load,thereby increased the strength and toughness of RAC.In addition,steel fiber reinforced RAC structures inevitably suffer from various possible impact loads during the service period,higher requirements are put forward for the bearing capacity and safety of RAC structures.However,at present,the studies on the design theory and test method of steel fiber reinforced RAC mainly focus on the performance under static load,but less attention was paid to the mechanical properties of steel fiber reinforced RAC under impact load.In this paper,the mechanical properties of steel fiber reinforced RAC under impact load were studied through experiments,theoretical analysis and microstructure analysis.The purpose is to provide reference and theoretical basis for later research works of the RAC and its application in practical engineering.The main research contents and conclusions are as follows:(1)The impact test device was designed with reference to the drop-weight impact test method of concrete recommended by ACI Committee 544,and the impact test of steel fiber reinforced RAC was carried out with the device.The effects of different recycled aggregate replacement rates,steel fibers content and steel fiber types on impact resistance of RAC were investigated.The test results show that the impact resistance of RAC gradually decreases with the increase of the replacement rates of recycled aggregate.However,the incorporation of steel fibers significantly improved the impact resistance of RAC,and its impact resistance increased with the increase in the amount of steel fibers.Meanwhile,it was found that the improvement effect of the end hook steel fiber on the impact resistance and crack resistance of the RAC is more significant than that of the corrugated steel fiber.(2)The mathematical statistical model of Weibull distribution was adopted to describe the experimental results and predict the failure probability of RAC.The Weibull distribution parameters were obtained by fitting analysis,and then the numbers of blows under different survival probability was calculated by the fitting regression parameters.The results indicated that the two-parameter Weibull distribution function can better describe the distribution law of the impact life for steel fiber reinforced RAC.Numbers of blows for steel fiber reinforced RAC specimens under different survival rates was predicted by regression calculation,and which provided theoretical analysis for practical engineering application of steel fiber reinforced RAC.(3)The changes in the macro-mechanical properties of fiber reinforced concrete is the reflection of the change in the microstructure at the macroscopic level.The microstructure of cement paste,the interface transition zone of aggregate/cement paste and the interface transition zone of fiber/cement paste were observed by scanning electron microscope(SEM).The effects of different recycled aggregates replacement rates on the strength of RAC,and the crack resistance and strengthening effects of steel fibers were explained from the micro level.