Study On The Mechanics And Durability Of Cementitious Materials Of Iron Tailings Fiber Under Carbonization/Salt Spray Environment

There are plenty of salt lakes in China,mainly distributed in northwest area.The main salt content and salt composition of each salt lake are not the same.Generally,salt lakes can be divided into four types according to the chemical composition of salt water in them,namely,chloride,carbonate,sulfate and nitrate.In recent years,with the development of society and the development of salt lake area,the number of engineering structures using concrete as the main material is increasing rapidly,and the research on mechanical properties and durability of corresponding materials is becoming more and more important.In this paper,the research on the basis of existing research results,through the iron tailings in cement base material mixed with different dosage of PVA fiber and carbon fiber,etc.,design the different dosage of hybrid fiber performance enhancements block iron tailings cement base material,through experiment and analysis,to study the iron tailings carbide/salt fog environment of fiber reinforced cement based materials mechanical performance and durability,The main research work is as follows:（1）Based on the cement-based material of iron tailings with a replacement rate of 40%,270 test blocks of cement-based material of iron tailings were designed and made by adding1.5%volume of PVA fiber and 0.3%,0.6%and 0.9%volume of carbon fiber,respectively.Simulated carbonization tests and mechanical property tests were carried out at ages of 0d,7d,14d,28d and 56d,respectively.The effects of fiber content and carbonization age on the main mechanical properties of cement-based materials were studied.The results show that the compressive strength,splitting tensile strength and flexural strength of the material increase first and then decrease with the increase of carbon fiber content at the age of 0d,40%iron tailings replacement rate and 1.5%PVA volume content.Compared with the other groups,the mechanical properties of the cement-based materials reinforced with 0.6%carbon fiber were better.Compared with the cement-based materials without fiber,the compressive strength,splitting tensile strength and flexural strength increased by 24.6%,33.9%and 11.7%,respectively.The compressive strength,splitting tensile strength and flexural strength increased by 10.9%,10.2%and 6.1%,respectively,compared with the cement-based material doped with PVA fiber alone.The compressive strength,splitting tensile strength and flexural strength increased by 6.1%,14.9%,8.1%and 5.6%,12.1%,8.4%,respectively,compared with the cement based materials mixed with 1.5%PVA volume and 0.3%and 0.9%carbon fiber volume.In addition,with the increase of carbonization age,the main mechanical properties of the material also increase.Generally speaking,the compressive strength,splitting tensile strength and flexural strength of the material are higher when the carbonization age is 56d.（2）the design and construction of the 270 the same as the working condition of the material performance of hybrid fiber reinforced iron tailings cement base material block,respectively through the ages of 0 d,7 d and 14 d and 28 d,56 d salt fog environment simulation and mechanical properties test,studied the different fiber content and salt fog ages on the influence of the main mechanical properties of iron tailings cement base material,At the same time,based on Weibull probability distribution and test results,the damage evolution equation of cement-based materials with mixed fiber iron tailings under salt spray environment is established.The results show that the compressive strength,splitting tensile strength and flexural strength of the material increase first and then decrease with the increase of carbon fiber content at the age of 14 days.Compared with the other groups,the mechanical properties of the cement-based materials reinforced by 0.6%carbon fiber are better.Compared with the cement-based materials without fiber,the compressive strength,splitting tensile strength and flexural strength are increased by 26.4%,20.2%and 38.8%,respectively.Compared with iron tailings cement-based material doped with PVA fiber alone,the compressive strength,splitting tensile strength and flexural strength increased by 10.4%,18.3%and 12.1%,respectively.Compared with the cement-based materials mixed with 1.5%PVA volume and 0.3%and 0.9%carbon fiber volume,the compressive strength,splitting tensile strength and flexural strength increased by 6.5%,10.1%and 6.4%and 5.5%,17.5%and 8.9%,respectively.In addition,with the increase of salt spray age,the main mechanical properties of the material increased first and then decreased.Generally speaking,the mechanical properties of most mixtures reached their peak at 14d and a few reached their peak at 28d.（3）Scanning electron microscopy was used to analyze the microstructure characteristics of cement-based materials of fiber-iron tailings under different fiber content,different carbonization and salt spray ages.Combined with the experimental phenomenon of macroscopic mechanical properties,the influence of microstructure structure changes on macroscopic mechanical properties was explained.The research results show that,in the process of material carbonization,Ca（OH）₂in cement-based material constantly reacts with CO₂to generate new Ca CO₃.The microstructure of Ca CO₃material is densier and the strength is higher,and carbon fiber and PVA fiber bond well with cement-based material.The pull-out effect of carbon fibers and the inherent toughness and ductility of PVA fibers lead to the better strength and toughness of the cement-based materials reinforced with hybrid fibers,thus improving the main mechanical properties of this material.In addition,the chemical reaction produced by the material in the salt spray environment,can generate some new substances such as Friedel salt without cementitious action,the new material particles are small,can partially fill the pores in cement-based materials,resulting in the internal structure of the material more compact,so as to improve the strength of the material;However,when the volume of new particles increases continuously,the original pores will rupture and some stress concentration will occur,which reduces the mechanical properties of the material.However,after mixing a reasonable number of different fibers,the destruction of pores and the extension of microcracks can be reduced,and the mechanical properties of the material can be improved.