Study On Flexural Toughness Of Hooked-end Steel Fiber Reinforced Concrete And Its Calculation Method

The extensive application of concrete has greatly promoted the development of contemporary water conservancy engineering.However,due to the disadvantages of concrete,such as low tensile strength,poor toughness,and easy cracking,as well as complicated hydraulic engineering conditions,hydraulic concrete structures often have to withstand many factors such as high load,high impact,fatigue,and erosion.Therefore,Higher requirements on the performance of concrete have been put forward in the construction of hydraulic engineering.Steel fiber reinforced concrete prepared by mixing a certain percentage of steel fiber into concrete,it can improve tensile,flexural,toughness and other properties while ensuring the excellent properties of concrete.At present,steel fiber reinforced concrete has been initially applied in hydraulic engineering,which can significantly improve the performance and service life of hydraulic structures.As one of the important indicators for measuring mechanical properties,the toughness of concrete refers to the material's ability to absorb energy from loading to failure.The great toughness of steel fiber reinforced concrete can meet the impact of hydraulic materials or structures in complex working conditions.Flexural toughness is often used as an index to evaluate toughness in actual engineering.Existing research proves that the flexural toughness of steel fiber reinforced concrete is not only related to the strength of the concrete matrix,but also to the strength,dosage,physical dimension,distribution state and type of the steel fiber.With the continuous improvement of concrete properties and the progress of steel fiber production technology,high-strength and high-anchor hooked-end steel fibers have emerged,but the impact of this new type of steel fiber on the flexural toughness of concrete has not been systematically studied.For this reason,this paper studies the influence of the dosage,physical dimension and type of hooked-end steel fiber on the flexural toughness of the steel fiber reinforced concrete based on the experiments.The main research contents are as follows:(1)Through the three-point bending test of the notched beam on 48 groups of 576 specimens with size of 150 mm×150 mm×550 mm,The strength of the concrete matrix,the dosage,physical dimension and types of steel fibers were used as test parameters.The influence of each factor on the load-deflection curve was analyzed by RILEM TC 162-TDF,and the influence of each factor on the flexural toughness was calculated by CECS13:2009.The results show that the load-deflection curve will be fuller and the flexural toughness will be better with the higher of the concrete matrix,the larger of the steel fiber dosage,aspect ratio,length and end hooks number within the range of test parameter changes.(2)The calculation method of mathematical statistics was used to compare the influence of various factors on the flexural toughness of steel fiber reinforced concrete.The results show that the flexural toughness of concrete before cracking mainly depends on the strength grade of the concrete matrix.After the concrete cracks,the steel fibers across the cracks gradually play a toughening role.The flexural toughness is mainly affected by the changes of steel fiber parameters.Dosage is the most important factor affecting flexural toughness.The physical dimension of steel fiber mainly affects the bonding effect between steel fiber and concrete matrix.The steel fiber end hook enhances the bonding effect through anchoring during the bonding phase of steel fiber and concrete,and consumes a lot of energy to improve flexural toughness by generating plastic deformation or crushing concrete during the pulling out of the steel fiber.Among the factors of the steel fiber itself,the effect of the steel fiber end hook on the flexural toughness is the largest.(3)Based on the flexural toughness test results of the notched beam in this paper and related literatures,a calculation method for evaluating the flexural toughness of steel fiber reinforced concrete was proposed,and its rationality is verified.