Study On Properties Of Iron Tailing Sand-Recycled Concrete Reinforced With Nano Metakaolin

With the rapid development of urbanization and iron and steel industry,a large number of solid wastes,mainly consisting of waste concrete and iron tail ore,are generated.A large number of accumulated waste concrete and iron tail ore not only occupy land but also cause environmental pollution.In order to solve a lot of waste concrete and Iron ore(Iron tailings sand,ITS)caused by the ecological environment problems,this article will Nano metakaolin(Nano metakaolin,NMK)mixed with Iron tail ore-recycled concrete,Studied under the different NMK content and ITS replace rate NMK on Iron tail ore-Recycled concrete(Iron tailings sand-Recycled concrete,the IRC)the compressive strength,splitting tensile strength,bending strength,the influence of In nanometer recycled concrete compressive strength,split strength,bending strength is the basis of establishing the model of mechanical strength analysis of correlation between the nano mechanical strength of recycled concrete.By chloride ion diffusion coefficient of the fast freeze-thaw test equipment,apparatus and concrete chloride ion erosion resistance and the durability of freezing-thawing resisting cycle performance test experiment,explore NMK chloride ion erosion resistance of the IRC and antifreeze performance impact.Through the SEM(Scanning electron microscopy,SEM),mercury intrusion method(mercury injection porosimetry,MIP),nitrogen adsorption method(Barret-Joyner Halenda,BJH)on recycled concrete porosity,pore volume and other characteristics of microstructure analysis,explores the NMK influence on IRC microstructure and the mechanical properties and durability performance improvement mechanism.In this paper,we study the following conclusions:(1)With the increase of ITS substitution rate,resulting in the dominant distribution of small particles in the area close to the aggregate surface,resulting in the formation of loose and porous structures around the aggregate.Therefore,the compressive,split tensile and fracture strength of IRC28 days all show a decreasing trend.Compared with Recycled concrete(RC),when the replacement rate of ITS is30%,the compression,split tensile and fracture strength of ITS recycled concrete decrease by 8.6%,8.1% and 19.4%,respectively.Compared with the ITS recycled concrete specimens without NMK,the change trend of compressive,split tensile and flexural strength of the nano-recycled concrete specimens with NMK replacement rate of 3%,5% and 7% also shows the same law,and the mechanical strength decreases with the increase of ITS replacement rate.(2)With the increase of NMK content,the compressive,tensile and flexion strength of nano-reclaimed concrete Specimens increased after decreased first.When the ITS replacement rate was 30%,the mechanical strength of nano-reclaimed concrete specimens with 5% NMK substitution rate increased the most compared with ITS recycled concrete specimens without NMK.The increase in compressive,tensile,and flexural strength is 15.2%,30.1%,and 28%,respectively.When the NMK substitution rate is 7%,the mechanical strength of NIRC specimens decreases by16.3%,23.6%,and 25%,respectively.(3)The effects of different NMK content and ITS substitution rate the chloride ion migration coefficient of recycled concrete is studied and the freeze-thaw cycle performance.The results show that the chloride ion migration coefficient of reclaimed concrete increases with the increase of ITS displacement.With the same ITS substitution rate,the chloride ion migration coefficient of nano-regenerated concrete first decreases and then increases with the increase of NMK substitution rate.When the replacement rate of ITS is 30% and the replacement rate of NMK is 5%,the chloride ion migration coefficient of ITS recycled concrete is reduced by 34.9%compared with that of ITS recycled concrete without NMK.When NMK is added,The relative dynamic elastic modulus decay rate and mass loss rate of nano-reclaimed concrete decrease is lower than that of IRC specimens without NMK.When the replacement rate of NMK is 5%,the mass loss rate and the relative dynamic elastic modulus decay rate reach the minimum value.Therefore,appropriate amount of NMK can improve the chloride penetration resistance and freezing resistance of IRC.(4)In order to study the effect principle of NMK on the microstructure of iron tailings sand-reclaimed concrete,Changes in interfacial transition zone and hardened cement mortar,Using SEM and MIP,BET more points and BJH method of recycled concrete pore volume and pore size distribution are analyzed.The experimental results showed that the incorporation of NMK made the IRC structure more dense,and improved the mechanical properties and durability of IRC.