Study On Pressure Sensitive And Mechanical Properties Of Iron Tailings Carbon Fiber Cement-based Materials Under Dry-Wet Cycles

Carbon Fiber Cement-Based Materials(CCM)has unique pressure-sensitive properties,which make it suitable for real-time health monitoring of structures after reasonable integration.The durability of this material and how to improve its pressure-sensitive performance are relatively less studied by scholars at home and abroad.Therefore,in this paper,a new type of Iron Tailings Carbon Fiber Cement-Based Materials(ICCM)was prepared by replacing some natural sand with a reasonable amount of iron tailings.Through the test and analysis of the test block,the influence of iron tailings replacement rate on its pressure sensitivity and mechanical properties was studied,and the durability of this test blocks under dry and wet cycles were studied.The main research work and results are as follows :(1)A total of 78 CCM and ICCM test blocks in 26 groups were prepared by using different contents of carbon fiber such as 0.2 %,0.4 % and 0.6 % and different substitution rates of iron tailings such as 15 %,30 % and 45 %.Through the mechanical properties test and analysis,the main mechanical properties of the above materials under different conditions were studied.The results show that the cube compressive strength and splitting tensile strength of ICCM are higher than those of CCM under different working conditions.When the carbon fiber content is 0.4 % and the replacement rate of iron tailings is 30 %,the compressive strength and splitting tensile strength of ICCM increase by 13.2 % and 10.6 %respectively compared with CCM.(2)A total of 39 test blocks in 13 groups were tested by electrode method which can measure the stress-resistivity change rate of materials in real time.The effects of different carbon fiber content and different iron tailings substitution rate on the pressure sensitive properties of CCM and ICCM were studied.The parameters such as stress(σ)-resistivity change rate(FCR)curve and average stress sensitivity coefficient()are used to reflect the general law and sensitivity of the change of pressure sensitivity of materials.The results show that with the increase of carbon fiber content and iron tailings replacement rate,the average stress sensitivity coefficient of the material increases first and then decreases.When the carbon fiber content is 0.4 % and the iron tailings replacement rate is 30 %,the average stress sensitivity coefficient of the material is larger.Compared with CCM,the value is increased by about 87.4 %.(3)A total of 234 groups of 702 CCM and ICCM test blocks were prepared by using the above-mentioned carbon fiber with different contents and iron tailings with different substitution rates.These test blocks were subjected to long-term dry-wet cycle tests in general atmospheric environment and sulfate environment.The results show that after 90 dry-wet cycles,the mass loss rate of ICCM test block in sulfate environment increases by 370 %,the relative dynamic elastic modulus decreases by 18.1 %,the compressive corrosion resistance coefficient decreases by 10.3 %,and the average stress sensitivity coefficient decreases by11.8 % compared with that in general atmospheric environment.(4)The effects of different carbon fiber content,different iron tailings replacement rate and different dry-wet cycle on the microstructure of CCM and ICCM were studied by nuclear magnetic resonance test and SEM scanning experiment.The results show that 0.4 % carbon fiber content can bear the load together when the material is compressed / pulled,and inhibit the development of cracks.The 30 % iron tailings replacement rate can optimize the gradation and improve the density of the material.With the increase of the dry-wet cycle period,in the sulfate environment,the cement products in the pores of the ICCM microstructure are first filled with expanded crystals formed by the reaction of SO42-.As the sulfate corrosion continues,the increase of corrosion products causes cracks inside the material,which provides a new channel for sulfate ions to enter the interior of the specimen.The internal corrosion of the material is aggravated.The macroscopic performance is that the surface mortar and the edge of the material are loose and cracked or even fall off,resulting in a decrease in various performance indicators,which explains the mechanism of ICCM being eroded by sulfate.