Experimental Research On Flexural Behavior Of Hybrid Steel Fiber Concrete With Two Grade Aggregate

Steel fiber reinforced concrete（SFRC）is widely used in many fields such as bridges,tunnels,water conservancy,buildings and so on because of its excellent physical and mechanical properties.In order to expand the scope of use of SFRC,combining with the National Natural Science Foundation of China”The investigation on toughness and fracture properties of steel fiber reinforced two-graded aggregate concrete”,the orthogonal test design is adopted.The factors taken into account are the volume ratio of steel fiber,the proportion of long steel fiber in hybrid steel fiber（hereinafter referred to as"long steel fiber ratio"）and the strength grade of concrete.In this paper,16 groups of orthogonal tests and 2 groups of control tests were designed to study the influence of hybrid different lengths of steel fiber include 31.5mm and 60mm on the working performance,compressive strength,splitting tensile strength and flexural properties of two-graded aggregate concrete,The main research contents and conclusions are as follows:（1）Through the slump test of 18 groups of concrete mixes,the effect of the hybrid steel fibers on the working performance of two-graded aggregate concrete mixture was studied.The results show that the slump of concrete mixture decreases with the increase of the volume ratio of steel fiber,and the influence of hybrid steel fibers on slump is small.（2）Through the standard cubic specimen compressive strength and splitting tensile strength test,the effect of the hybrid steel fibers on the compressive strength and splitting tensile strength of two-graded aggregate concrete was studied.The results of range analysis and variance analysis show that the volume fraction of steel fiber and the proportion of long steel fiber have no significant effect on the compressive strength of C30 and C60 concrete.The volume fraction of steel fiber and the concrete strength grade have a significant effect on the splitting tensile strength,splitting tensile strength increases with the increase of steel fiber volume ratio,and decreases with the increase of concrete strength grade increased,but the ratio of long steel fiber has no significant effect on splitting tensile strength.（3）Through the four-point bending test of 150mm×150mm×550mm specimens,the influence of the hybrid steel fibers on the flexural properties of two-graded aggregate concrete was studied.The results show that the strength grade of concrete and the volume fraction of steel fiber have remarkable effects on the flexural strength and flexural toughness ratio.The change of the proportion of long steel fiber has little influence on the flexural strength,flexural toughness index and flexural toughness ratio,the flexural strength and flexural toughness index I₅、I₁₀、I₂₀ of C30 and C60 hybrid steel fiber reinforced concrete increase with the increase of the volume fraction of steel fiber,and there is no obvious regularity with the change of the proportion of long steel fiber.On the basis of this experiment,the formulas for calculating the flexural tensile strength of C30 and C60 hybrid steel fiber concrete with two grade aggregate are fitted in combination with the previous research results of the research group.（4）Based on the Weibull distribution and the logarithmic normal distribution,the strain equivalent principle is adopted,and considering the influence of the volume fraction of steel fiber and the proportion of steel fiber with two different lengths,the damage model of hybrid steel fiber reinforced two-graded aggregate concrete under bending load is established and the model is in good agreement with the experimental results.