Effect Of Steel Fiber Shape And Content On Impermeability And Frost Resistance Of Two-graded Aggregate Concrete

Compared with steel fiber reinforced concrete(SFRC)with single-graded aggregate,the cement content,adiabatic temperature rise,and drying shrinkage of SFRC with two-graded aggregate at the same strength level are significantly reduced.As a good toughening and crack resisting material,it is used in the hydraulic concrete structure.However,due to the characteristics of frequent contact with environmental water in the process of use,the high requirements of impermeability and frost resistance durability are also put forward,which directly affects its application in water conservancy projects.Therefore,under the background of ecological protection and high-quality development in the Yellow River Basin,it is of great practical significance to study the impermeability and frost resistance durability of SFRC,which can provide theoretical guidance for China’s water conservancy engineering,especially the proposed and under construction water conservancy engineering in the Yellow River Basin.Given this,this paper studied the influence of three different shapes of hookedend steel fiber(3D,4D,and 5D)and different volume content(0%,0.5%,1.0%,1.5%,and 2.0%)on the performance of two-graded aggregate concrete,especially the impermeability and frost resistance.The characteristics of pore structure were studied to reveal the mechanism of their influences on impermeability and frost resistance.The main contents were as follows:(1)Through the slump tests of concrete mixture,the influence of the shape and volume content of steel fibers on the working performance of two-graded aggregate concrete mixture was studied.The results show that the flowability of concrete mixtures mixed with different steel fiber shapes is lower than that of the matrix concrete.The slump is less affected by the steel fiber shape when the steel fiber content is the same,and the corresponding steel fiber shape from large to small is 3D,4D,and 5D.The slump decreases with the increase of steel fiber volume content.(2)Through the compressive and splitting strength tests of concrete,the influence of the shape and volume content of steel fibers on the compressive strength and splitting strength of the two-graded aggregate concrete was studied.The results show that the compressive strength is improved by the addition of steel fibers with different shapes and increases with the increase of the steel fiber volume content,increasing firstly and then decreasing.The splitting strength is greatly affected by the shape and volume content of steel fiber.The splitting strength of 3D,4D,and 5D steel fibers increases by49.1%,73.0%,and 84.0%,respectively,and increases with the increase of steel fiber content.The splitting strength is the highest at 2.0% vol and 84.0% higher than that of the matrix concrete.(3)Through the water permeability tests of the concrete,the influence of the shape and volume content of steel fibers on the impermeability of two-graded aggregate concrete was studied.The results show that the impermeability is improved little by the addition of steel fibers with different shapes.With the increase of the steel fiber volume content,the degree of improvement on the impermeability first increases and then decreases.The impermeability is the most improved than that of the matrix concrete,at this time,the average seepage height is the smallest with a decrease of 34.9%,and the impermeability grade is the highest with an increase of 30%.(4)Through the single-side freeze-thaw tests of the concrete,the influence of the shape and volume content of steel fibers on the frost resistance of two-graded aggregate concrete was studied.The results show that the frost resistance is improved little by the addition of steel fibers with different shapes.With the increase of the steel fiber volume content,the degree of improvement on the frost resistance first increases and then decreases.The frost resistance is the most improved than that of the matrix concrete,at this time,the mass of spalling material is the biggest with an increase of 25.97%,and the relative dynamic elastic modulus is the minimum with a decrease of 8.31%.(5)Based on the fractal theory,the influence of the shape and volume content of steel fibers on the pore structure of the concrete was studied by the concrete pore structure tests.The relationships between the fractal dimension and the pore structure parameters,steel fiber volume content,number of freeze-thaw cycles,relative dynamic elastic modulus,and peeling material mass were established from the perspective of the microscopic pores.The results show that the fractal dimension of the pore structure can be used as an index to evaluate the frost resistance of SFRC with the two-graded aggregate.The larger the fractal dimension is,the greater the relative dynamic modulus is,the smaller the peeling material mass is,and the better the frost resistance is.