Research On Pore Structure And Mechanical Properties Of Basalt Fiber Reinforced Concrete Under Freezing And Thawing Conditions

In order to analyze the effect of freeze-thaw medium type,basalt fiber content and freeze-thaw cycle on the freeze-thaw resistance,compressive strength loss and pore structure damage degradation of concrete,the freeze-thaw test,pore structure analysis test and compression test of concrete were performed.Meanwhile the fractal dimension,as a representative pore structure parameter of concrete to study its relationship with concrete frost resistance and compressive strength,were calculated by fractal model that established based on fractal theory.The simple model of concrete compressive strength and pore structure was established based on the fractal dimension.The test results are as follows:(1)The effect sequences of the freeze-thaw medium for the scaling on the surface of the specimen is as follows: salt,water and aircraft deicing fluid.The mass loss and the relative dynamic elastic modulus loss of the specimen during freeze-thaw cycles from high to low are salt,water and aircraft deicing fluid.(2)During freeze-thaw cycles in both water and salt solution,the mass loss of ordinary concrete specimens increases sharply with the number of freeze-thaw cycles;the relative dynamic elastic modulus drops sharply with the number of freeze-thaw cycles;but the mass loss and relative dynamic elastic modulus of basalt fiber reinforced concrete specimens are slightly affected with the number of freeze-thaw cycles.(3)During freeze-thaw cycles in both water and salt solution,the compressive strength of ordinary concrete decreases linearly with the increase of freeze-thaw cycles and the compressive strength of concrete with different basalt fiber content increases linearly with the increase of the fractal dimension.The compressive strength loss rate of concrete is below 2% after 16 freeze-thaw cycles and begin to increase after 32 freeze-thaw cycles.The compressive strength loss rate under salt-freezing conditions is higher than that under water-freezing conditions.The concrete with 0.2% basalt fiber content has the lowest loss rate of compressive strength after freezing and thawing cycles.(4)Before freezing and thawing cycle,the air content,the average chord length of pores and the air void spacing coefficient of basalt fiber reinforced concrete decrease linearly with the increase of the fractal dimension and decrease gradually with the increase of basalt fiber content.The surface area of pores increases exponentially with the increase of the fractal dimension and increases with the increase of basalt fiber content.The fractal dimension increases linearly with the increase of basalt fiber content and the linear correlation is very high,which can characterize quantitatively the pore structure of concrete.(5)As the number of freeze-thaw cycles in both water and salt solution,the pore specific surface area decreases,the spacing coefficient and the average chord length increase,the frequency of the small pore chord lengths decreases and the frequency of the large pore chord increases.The variation ranges of the above parameters are wider under salt-freezing than water-freezing conditions,and the concrete with 0.2% basalt fiber content has the least freeze-thaw damage.(6)The fractal dimension shows good positive and negative correlation with relative dynamic elastic modulus and cumulative mass loss,respectively.The fractal dimension and the total volume of pores with the diameter in the range of 100-500?m were chosen as parameters and a simple model between the fractal dimension and the compressive strength of basalt fiber reinforced concrete was established.