Nondestructive Testing Of Fiber Distribution And Tensile Properties Of Steel Fiber Reinforced Concrete

Steel fiber reinforced concrete(SFRC)has developed rapidly in modern civil engineering due to its excellent mechanical properties such as tensile strength,toughness,and impact resistance.The uniformity and directionality of fiber distribution in concrete matrix have a significant impact on its crack resistance and toughness.There are significant differences in fiber distribution in SFRC with different working properties.In this paper,for plastic,flow,large flow,and self compacting SFRC specimens,non-destructive testing,electromagnetic induction,and image analysis methods are used to study fiber distribution uniformity and directionality,and uniaxial tensile and flexural tests are conducted to establish the relationship between nondestructive testing and tensile properties of SFRC fiber distribution.The main research contents are as follows:(1)Design calibration tests to conduct inductance tests on self compacting SFRC with0.4%～1.2% steel fiber content and 0°～90° fiber distribution direction,and test the inductance parameters and inductance increments of SFRC.It is found that there is a linear relationship between the steel fiber content and the inductance parameters.By testing the inductance increments in the three main axis directions of the test piece,the spatial distribution of the fibers can be determined,thereby determining the feasibility of applying the electromagnetic induction method to testing the distribution of SFRC fibers.At the same time,conduct inductance testing and image processing analysis on the self compacting SFRC specimen after the bending and tensile test,and use the phase sum coefficient to compare the similarity of the fiber spatial distribution obtained from the inductance test and image analysis to verify the accuracy of the electromagnetic induction method applied to testing the fiber spatial distribution.(2)Using large head specimens,uniaxial tensile tests were conducted on self compacting SFRC with steel fiber content of 0% to 1.2%,plasticity,fluidity,and high fluidity SFRC with steel fiber content of 0.8%.The effects of different steel fiber content and different working properties on the axial tensile properties of SFRC were studied.The results show that for self compacting SFRC,when the volume fraction of steel fibers is between 0% and 1.2%,the axial tensile strength of concrete increases with the increase of the volume fraction of steel fibers,reaching the maximum at 1.2%,which is 2.47 times the axial tensile strength of plain concrete.When the volume fraction of steel fiber is 0.8%,the axial tensile strength of SFRC decreases as the workability of concrete decreases,and the axial tensile strength of self compacting SFRC is 1.26 times that of plastic SFRC.Based on artificial statistics of the fiber distribution in the failure section of axial tensile specimens,it is found that the number of fibers in the section and the fiber dispersion coefficient are closely related to the axial tensile performance,and the fiber dispersion coefficient decreases with the decrease in the workability of concrete.The inductance test on axial tensile specimens shows that the fiber distribution ratio in the axial tensile direction decreases as the workability of concrete decreases.The relationship between the electromagnetic induction method,the inductance increment,and the axial tensile strength,is established.(3)Using beam type specimens,flexural and tensile tests were conducted on self compacting SFRC with steel fiber content of 0% to 1.2%,and plastic,fluidity,and high fluidity SFRC with steel fiber content of 0.8%.The effects of different steel fiber content and different working properties on the flexural and tensile properties of SFRC were studied.The results show that adding 1.2% steel fiber can increase the flexural tensile strength of self compacting SFRC by 2.41 times.The flexural and tensile strength of concrete is positively correlated with its workability.The volume fraction of steel fiber is0.8%,the flexural tensile strength of SFRC gradually increases with the enhancement of concrete fluidity.Using artificial statistics on the fiber distribution in the failure section of SFRC flexural tensile specimens,the results show that the flexural tensile strength increases with the increase in the number of fibers in the failure section and the dispersion coefficient,which is proportional to the volume fraction of steel fibers and the workability of concrete.The approximate ratio of the fiber distribution in the main axis direction of the concrete of the flexural tensile specimen tested by the inductance test is CIx: CIy: CIz=2.56:1.82:1.The relationship between the electromagnetic induction method,the inductance increment,and the flexural tensile strength,is established.