Effect Of Fibers On Mechanical Properties And Freeze-thaw Behaviour Of Self-consolidating Concrete

In the cold regions of northern China,the concrete freeze-thaw cycles is the primary causes of concrete performance degradation and structural damage.In this paper,the problems of flexural failure and self-consolidating concrete structures freeze-thaw damage subjected to freeze-thaw cycles in cold regions of northern China are studied from freeze-thaw cycles test,three-point bending test of notched beam and 3D laser scanning test.The purpose is to evaluate the effect of fibers on the frost resistance of self-consolidating concrete by applying fractal theory and freeze-thaw damage theory.it provides guidance for the service life and the frost resistance and durability design of self-consolidating concrete structures in cold regions of northern China.The main content of this paper is as follows:(1)According to the relevant domestic and foreign specifications,the workability test of self-consolidating concrete is carried out,The slump flow and slump-flow time T500 of freshmixed self-consolidating concrete can be measured by the slump flow test.The slump flow and T500 can be used to evaluate the flow properties and filling properties of fresh-mixed selfconsolidating concrete.Through the J-ring flow test,the J-ring Δh and J-ring flow and the difference between the concrete slump flow and the J-ring flow(PA)can be measured by the J-ring flow test.The index evaluates passing ability of the fresh-mixed self-consolidating concrete.The percentage of the static segregation measured by a standard sieve test is used to detect the segregation resistance of the self-consolidating concrete.The test results show that the incorporation of fibers can reduce the slump flow of self-consolidating concrete and increase the T500 value;the incorporation of fibers can reduce the J-ring flow of selfconsolidating concrete and increase the difference of J-ring height.(2)Through the rapid freeze-thaw cycles test of self-consolidating concrete specimens,the effects of fiber and freeze-thaw cycles on freeze-thaw damage of concrete specimens are studied.The results show that: The effects of macro steel fiber on the mass loss rate of concrete after freeze-thaw cycles is greater than that of macro polypropylene fiber.The hybrid fibers have positive hybrid effect on mass loss rate.As the number of freeze-thaw cycles increases,the ultrasonic wave velocity of the specimens are more sensitive to the concrete freeze-thaw damage than the dynamic elastic modulus,and the test effect is more significant.(3)Through the test of bending flexibility of specimen after freeze-thaw cycles,the effect of fiber type and fiber contents on the flexural properties index of each specimen after freezethaw cycles is studied.The results show that as the time of freeze-thaw cycles improves,flexural resistance of concrete beam can be reduced obviously,with the increase of macro steel fiber and macro polypropylene fiber content,flexural resistance of concrete beam can be improved.When the time of freeze-thaw cycles is declined,the mixed of steel fibers and polypropylene fibers shows positive hybrid effect on the capacity absorption of concrete beams.When the time of freeze-thaw cycles is improved,the hybrid effect is not significant.(4)After the three-point bending test of the notched beam,the 3D laser scanning test of the fracture surface is carried out.The test achieves the 3D’s visualized reconstruction of specimens’ fracture surface after freeze-thaw cycles.Statistical analysis of Z-coordinates of specimens’ fracture surface,its pattern after freeze-thaw cycles are studied based on standard deviation and fractal dimension theory.The test results show that as the number of freeze-thaw cycles increases,the Z-coordinate standard deviation of the fracture surface of the specimen increases,and the degree of dispersion shows more obvious.The specimen’s fractal dimension is related to the fiber content.As the number of freeze-thaw cycles increases,the fractal dimension D of the concrete section increases.