Study On Properties Of POM Fiber Reinforced Concrete

In recent years,Polyformaldehyde(POM)has developed a kind of high strength,high elastic modulus,with excellent acid and alkali corrosion resistance,outstanding mechanical properties,excellent dispersion in the composite matrix fiber.At present,most research on fiber concrete foeuses on polypropylene fiber and steel fiber,but few on POM fiber.In this paper,the POM fiber content and the mechanical properties,durability,thermodynamic coupling properties and post-high temperature properties of POM fiber concrete under the optimal content were studied.Five water-binder ratios(0.50,0.45,0.40,0.35 and 0.30)were used to test the compressive strength,split tensile strength and flexural strength of concrete.The differences between PFC and benchmark concrete were compared to analyze the influence of PFC on the mechanical properties of concrete.At the same time,five water-binder ratios of concrete were used for the dry and wet cycle test of sulfate resistance,impermeability test and freeze resistance test to compare and study the influence of POM fiber on the durability of concrete.MTS 810 material testing system was used to study the damage characteristics,damage law and damage constitutive model of concrete under the coupled action of heat and force.The performance change rule of concrete under different cooling mechanism under high temperature was studied by using high temperature furnace.The main conclusions are as follows:(1)1.2kg/m3 dosage is the optimal dosage for this test.The compressive strength,split tensile strength and flexural strength of POM fiber concrete with five water-binder ratios were studied.It was found that the POM fiber had little effect on the eompressive performance of concrete,but enhanced the split tensile and flexural performance of concrete significantly.(2)The lower the water-binder ratio,the stronger the resistance of concrete to sulfate attack.POM fiber can improve the resistance of concrete to sulfate attack.The frost resistance of POM fiber concrete is better than that of reference concrete.POM fiber is beneficial to enhance the intermal compactness of concrete and improve the impermeability of concrete.(3)After 400?,concrete under the action of outer load pore is gradually being close-grained,and producing larger disturbance.The temperature change has a larger effect on concrete performance.The thermal decomposition of CaCO3 in aggregate leads to the destruction of concrete structure after 700?,which is insufficient to withstand extermal loads,and the thermal strain decreases gradually.During the heating process,the concrete expands under the influence of temperature and generates thermal strain.The incorporation of fiber can restrain the thermal deformation of concrete caused by temperature effectively(4)Based on acoustic emission parameters,the Ds value of high-temperature thermal damage of concrete and the DT value of damage in loading stage are defined.The Ds value curve of thermal damage can reflect the deterioration trend of concrete in high-temperature environment.The thermal damage caused by high temperature has a great impact on the performance of concrete.In the loading stage,the damage Dr value can well describe the process of concrete failure at this stage.The damage D value was modified in consideration of the high-temperature loading test environment.The damage constitutive model was established in the loading stage,which was applicable to all temperature segments.The single factor analysis method was adopted to analyze the material coefficient in the constitutive model which was established.The coefficients v and q only affect the change trend of stress and reflect the strength of the material,while the coefficient p has an impact on both stress and strain,reflecting both the strength and ductility of the material.At the same time,the constitutive model of concrete at 400?is studied,and the constitutive equation of concrete at 400? is obtained by three groups of stable and reliable data calculation.(5)After high temperature cooling naturally,the compressive strength of concrete firstly rises,and then decreases gradually,at 200? and 400?,the concrete compressive strength is higher than normal temperature,and immersion cooling secondary damage of concrete.The compressive strength showed a trend of gradual decline.Adding POM fiber can improve the compressive strength of concrete at high temperature.The difference between the splitting strength of POM fiber concrete and the reference concrete in the two cooling methods is not significant,and the POM fiber has little influence on the splitting strength of concrete at high temperature.With the increase of temperature,the relative dynamic modulus of concrete decreases gradually and the damage D value increases gradually.Meanwhile,the addition of POM fiber can improve the dynamic elastic modulus of warm concrete and reduce the damage D value of concrete after high temperature and delay the damage of concrete at high temperatureIn the high temperature environment,a series of reactions occur in the concrete,resulting in the loss of concrete quality.