Mechanical Properties Of Calcium Sulfate Whisker Concrete And Carbonization Under Bending Load And Chloride Ion Permeability Performance

During the service of railway reinforced concrete bridges,the beam may be cracked by external load.At the same time,concrete in the beam will be affected by durability factors such as carbonization and chloride ion erosion.Cracking of the beam will make the situation more serious.This paper investigated a way in which increase the elastic modulus of concrete is achieved by adding calcium sulfate whiskers to the concrete,for the purpose to control the cracking of concrete under bending load.At the same time,the development of mechanical properties of different content of calcium sulfate whisker concrete at different age were investigated under combination of the durability factors such as carbonization,bending load and carbonization coupling,chloride ion erosion and chloride ion attack after carbonization.The main research results are as follows:(1)Through the basic mechanical properties test of concrete with two different whiskers content,the development of compressive strength and elastic modulus of calcium sulfate whisker concrete with age was derived:Compared with plain concrete,the compressive strength and elastic modulus of calcium sulfate whisker concrete at different ages have increased greatly.With the increase of whisker content,the compressive strength and elastic modulus of concrete decrease significantly.(2)Scanning electron microscopy image shows that the calcium sulfate whiskers are in good connection with the concrete.The morphologies of calcium sulfate whiskers in the cement paste can be clearly spotted in the early stage of hydration.The slurry gradually wraps around the surface of the whisker and forms a spatial supporting structure with the concrete hydration product;some calcium sulfate whiskers straddle the micro cracks inside the concrete,connecting the two ends of the crack,hindering the development of the crack;some whiskers fill the internal pores of the concrete,increase the compactness of concrete.(3)Considering the influence of calcium sulfate whisker content and curing age on the elastic modulus of calcium sulfate whisker concrete,the three-phase model of concrete and the Weibull distribution theory were used to establish the elastic modulus of calcium sulfate whisker concrete with time.The prediction model was established and the validity of the model was verified by experimental results.(4)Concrete load-carbonization and carbonization-chlorine intrusion test:The self-anchoring method was used to load different amounts of calcium sulfate whisker concrete specimens,followed by rapid carbonization test to measure the specimens carbonization depth at different carbonization ages.The electric flux test was carried out on concrete specimens of different carbonization ages,and the influence of carbonization on chloride ion erosion was investigated.The results show that the ability of concrete with calcium sulfate whisker to resist carbonization is significantly improved compared with ordinary concrete.However,with the increase of whisker content,the ability of concrete to resist carbonization decreases.The load has a great influence on the carbonation resistance of calcium sulfate whisker concrete.The carbonization depth of the compression zone of the specimen is smaller than the carbonization depth of the tension zone,and the gap is more significant with the increase of the tensile force.The concrete with calcium sulfate whisker has a smaller electric flux than plain concrete at different carbonization ages,and the gap gradually decreases with the increase of carbon age.(5)Considering the load sharing effect of calcium sulfate whisker in concrete and the stress characteristics of concrete beam section under bending load,the uneven distribution of stress on the section is taken as the influencing factor,and the strip method is used to accurately calculate the bending.The paper accurately calculates the carbonation depth of concrete sections under bending loads.According to Fick’s second law,considering the influence of carbonization on chloride ion permeability,the influence parameters of carbonization on chlorine intrusion are proposed,and the existing chloride ion permeation model is modified.By comparing the experimental data with the model calculation results,the model agrees well with the experimental results.(6)The carbonization model under the bending load of calcium sulfate whisker concrete and the chlorine intrusion model under carbonization were substituted into COMSOL.The finite element analysis of the carbonization and chlorine intrusion depth of calcium sulfate whisker concrete members is performed.