Study On Frost Resistance Of Mineral Powder Reinforced Fiber Concrete To Mixed Salt

Freeze-thaw cycles and salt corrosion are the main causes of insufficient durability of concrete,and the damage caused by them has a coupling effect.In order to research the durability of Fiber reinforced Concrete(FC)in extreme environments,Silica Fume(SF)and Secondary Aluminum Dross(SAD)were used as mineral powder reinforcement materials in this paper.The effects of two kinds of mineral powder to replace the cement on the compressive strength,flexural strength,splitting tensile strength,compressive strength after salt freezing,flexural strength after salt freezing,splitting tensile strength after salt freezing,mass loss and relative dynamic elastic modulus loss of fiber reinforced concrete were studied.The fiber types are the polyethylene fiber and cellulose fiber,and the content of both is 0.9 kg/m~3.The mass fraction of one kind of mineral powder replacing cement is 2.5%,5%,7.5%and10%,and the mass fraction of equal mixed mineral powder replacing cement is 5%and 10%.In this paper,the microstructure,interface elements and hydration mechanism of concrete were analyzed by Scanning Electron Microscope(SEM)and Energy Dispersive Spectrum(EDS),and the prediction model of salt freezing damage of concrete was studied.The main research results and conclusions are as follows:(1).The results of concrete mechanics test show that:(1)With the increase of mineral powder content,the mechanical strength of SF concrete increases,but the mechanical strength of SAD concrete decreases.(2)For the damage rate of compressive strength after salt freezing,splitting tensile strength after salt freezing and flexural strength after salt freezing,the average strength damage rates of SF test group were 6.19%,-23.19%and 28.06%,respectively.The average strength damage rates of SAD test group were 12.09%,17.84%and 15.59%,respectively.(2).The experimental results of the durability of concrete mixed salt freezing show that:(1)After 200 cycles,the mass loss rate of FC specimens was 1.162%,and the mass loss rates of SF test group,SAD test group and SF-SAD test group were0.470%,2.585%and 1.989%,respectively.The relative dynamic elastic modulus of FC specimens was 0.803,and the relative dynamic elastic modulus of SF test group,SAD test group and SF-SAD test group were 0.889,0.906 and 0.915,respectively.(2)Through SEM and EDS tests,it is found that SAD will lead to an increase in air content of concrete,and the pores formed are spherical micropores with regular shape.After salt freezing cycle,the Cl element of FC specimen,SF test group and SAD test group increased by 0.76%,0.08%and 0.13%respectively,and the S element increased by 1.53%,0.87%and 0.45%respectively.(3).The research results of concrete salt freezing damage prediction model show that:(1)The determination coefficients of the two-parameter Weibull distribution model,the univariate cubic polynomial model and the Stirling exponential function model are basically above 0.90,and the fitting accuracy of the univariate cubic polynomial model is the highest.(2)After predicting the service life of concrete based on the univariate cubic polynomial model,it is found that the final salt freezing cycles of FC specimens are 282 times.The final salt freezing cycles of the SF test group,the SAD test group and the SF-SAD test group were all more than 310 times.