Study On Mechanics And Chlorine Resistance Of PVA Fiber Ceramsite Concrete

The concrete structure must not only meet the relevant mechanical performance requirements,but also withstand various environmental erosion effects during the service period.How to improve the durability of concrete under different service environments has become a hot spot in the engineering community.PVA(polyvinyl alcohol,PVA)fiber ceramsite concrete’s relavant engineering applications have gradually increased in recent years due to its advantages of light weight,high strength,resistance to chloride salt erosion and cracking,etc.Scholars at home and abroad have done many researches on the mechanical properties of PVA fiber ceramsite concrete,but few researches have been carried out on its durability.This paper conducts experimental researches on the mechanical properties and the resistance to chloride salt erosion of PVA fiber ceramsite concrete.The laws of compressive strength,electrical resistivity and chloride ion concentration of PVA fiber ceramsite concrete are explored.The main work completed in the paper is as follows:(1)Using PVA fiber length,volume content,and curing age as the test parameters,complete the mechanical properties and the resistivity tests of 126 groups(378 pieces)of test blocks.The test results show that with the increase of the PVA content,when the fiber length is 12 mm and the content is 1.2kg/m3,the compressive strength of test block reaches the maximum.In the 28 d drying state,the best condition is that the fiber length is 9mm and the content is 0.4kg/m3.Compared with the blank control group,the strength increased by 73.2%,14.6%,18.3%,respectively;Compared with the blank control group,when the fiber length is 9mm and the content is 1.2kg/m3,the increase in flexural strength is 35.1%;When the fiber length is 12 mm and the content is 0.8kg/m3,the increase in splitting tensile strength is 25.9%;When the fiber length is 6mm and the content is 0.8kg/m3,the increase in compressive strength is 22.4%.The changing law of resistivity is that it first decreases and then rises with the increase of fiber content.There is no inevitable correlation between the resistivity and compressive strength of the 3d and 28 d specimens.There is a good non-linear relationship between the 28 d compressive strength of the PVA fiber ceramsite concrete after drying and the fiber content.(2)Under the condition of fixed fiber content,with PVA fiber length as the main test parameter,52 groups(156 pieces)of test blocks under the three ages of 28 d,56d and 84 d were tested for the resistance to chloride salt erosion and the chloride ion migration coefficient and the chloride ion concentration.The test results show that there is a good non-linear correlation between the compressive strength of PVA fiber ceramsite concrete eroded by chloride salt and the fiber content.The compressive strength of the specimens increases first and then decreases with the increase of fiber content while the resistivity first decreases and then rises.The resistivity reached the lowest peak value when 6mm,9mm and the fiber content is 0.8 kg/m3.The resistivity value was the smallest at 12 mm,1.2 kg/m3.When the fiber length is 6mm、9mm and the content is 0.8 kg/m3,the resistivity reaches the lowest peak value.When the fiber length is 12 mm and the content is 1.2kg/m3,the resistivity is the smallest.(3)The chloride ion mobility coefficient after salt etching increases first and then decreases with the fiber content increases while the chloride ion concentration first decreases and then rises.The chloride ion concentration and chloride ion mobility coefficient of 6mm and 9mm both reach peak at 0.8 kg/m3.The chloride ion migration coefficient reaches the maximum at the content of 1.2 kg/m3 at 12 mm while the chloride ion concentration value reaches the minimum.The chloride ion migration coefficient value of PVA fiber ceramsite concrete decreases with the increase of resistivity,showing an inverse proportional function relationship,and conforms to the Nernst-Einstein equation.(4)Thinking about the binding capacity of ceramsite and chloride ions in concrete,the defects of ceramsite concrete itself and the attenuation effect of chloride ion diffusion coefficient,the M Maage model was modified.The chloride ion concentration model and chloride ion migration coefficient model were derived.The revised M Maage model and chloride ion concentration model are verified with test data.