Experimental Study On Carbonization Performance Of Hybrid Fiber Reinforced Iron Tailings Sand Concrete

Iron tailing sand is a kind of mineral waste.Open storage is a common treatment method of iron tailing sand,which not only has a great impact on the ecological environment,but also occupies a lot of land resources.Therefore,in order to protect the ecological environment and waste utilization,a moderate amount of iron tail mineral sand is used instead of ordinary concrete natural sand in the preparation of iron tail sand concrete,and study by adding suitable amount of hybrid fiber to enhance tail of iron ore under the environment of the mechanical properties and carbonation of concrete durability,etc.,and provide support for engineering application of this material.The main research contents and results are as follows:（1）Referring to the existing research results of the project team,225 ordinary concrete and iron tailing concrete test blocks were prepared by orthogonal experimental design and standard production and curing with 0%,15%,30%,50%and 70%iron tailing sand replacement rates,and through mechanical property tests and carbonization environment simulation.The effects of substitution rate of iron tailing sand and carbonation depth on mechanical properties of concrete materials were studied.The results show that with tail of iron ore,the increase of the replacement rate,the compressive strength,splitting tensile strength,elastic modulus and peak strain were first increases then decreases,30%iron tail sand replacement rate of compressive strength,splitting tensile strength increased by 7.6%and 17.7%respectively,generally replacement rate is 30%when the material has good mechanical properties;With the increase of the substitution rate of iron tailing sand,the carbonization depth of the material decreases first and then increases,and the carbonization depth is small when the substitution rate of 30%is the same.（2）In the above iron tailing sand concrete,1.5%steel fiber is added,and 0%,0.25%,0.5%and 0.75%PVA fiber is added respectively to form hybrid fiber.720 mixed fiber reinforced iron tailing concrete test blocks are prepared.Through mechanical properties and carbonization environment simulation tests,The effects of iron tailing sand substitution rate,single-doped steel fiber,PVA fiber content and carbonation depth on the mechanical properties of the material were studied.The results show that the compressive strength and other mechanical properties of the concrete doped with 1.5%steel fiber are higher than those of the ordinary iron tailings concrete,and the carbonation depth is relatively smaller;When mixing 1.5%steel fiber and different amounts of PVA fiber,the compressive strength of mixed fiber iron tailings concrete increases first and then decreases with the increase of PVA fiber content.When the replacement rate of 30%iron tailings sand is combined with 1.5%steel fiber content and 0.5%PVA fiber content,the mechanical properties of the material are better.The compressive strength,splitting tensile strength and axial compressive strength increased by 16%,22.9%and 14.7%,respectively;Under the same circumstances,the carbonation depth of the material decreases first and then increases.Relatively speaking,the carbonation depth of the material is small when the iron tailings sand substitution rate is 30%,the steel fiber content is 1.5%and the PVA fiber content is 0.5%.（3）Based on the mechanical properties and carbonation test results of the above materials,the carbonation depth prediction model of mixed fiber iron tailings concrete was established by using carbonation ages of 0d,7d,14d,28d and 56d,referring to the existing carbonation depth prediction model of ordinary concrete,and compared with the test results.The results show that with the increase of carbonization age,the compressive strength,splitting tensile strength and carbonization depth of the material increase,but the peak strain relatively decreases,indicating that the brittleness of the material increases.（4）Using nuclear magnetic resonance（NMR）technology,this paper analyzes the different tail of iron ore under different carbonization age substitution rate and tail of iron ore,the changing rule of the pore structure of concrete,at the same time using scanning electron microscopy（SEM）method,hybrid fiber are discussed under different carbonization age tail of iron ore,the microstructure of concrete characteristics,and compared with macro mechanical properties test was carried out.The microscopic test results show that the replacement rate of iron tailing sand has a significant effect on T₂ relaxation spectrum and pore structure.When the replacement rate of iron tailing sand is 30%,the main peak signal and T2 relaxation spectrum area are small,indicating that the total porosity of the material is small at this replacement rate.Referring TO the existing pore-compressive STRENGTH model,the fitting curve,fitting equation and regression parameters of the new pore-compressive strength of the corresponding materials are given by statistical analysis of the NMR test data.In addition,with the increase of carbonation age,the porosity and pore size of the above materials decrease,and the strength and brittleness of the materials increase.