Evaluation Of Hybrid Fiber Reinforced Concrete Toughness

Fiber reinforced concrete is one of the new composite materials that developing the fastest. In consideration of the engineering economy, in order to obtain the required characteristics of the fiber concrete and make cost lower, sometimes two or more than two kinds of fiber composite are used, this is called hybrid fiber reinforced concrete. For the application of ultrahigh strength concrete structure, the toughness of concrete is particularly important. Currently, Technical Specification for Fiber Reinforced Concrete Structures (CECS38:2004) is a steel fiber reinforced concrete structural design theory and method thatare mainly based on strength index, but it hasn’t madethe relevant provisions onhybrid fiber reinforced concrete material properties and structural design so far. At the same time, application of hybrid reinforcedfiber concrete in tunnel engineering, airport runway, bridge pavement, nuclear waste storage is increasingyear by year. And this raises new issues about the toughness evaluation and structural design method of hybrid fiber reinforced concrete. This paper conducts a systematic study of evaluation of flexural toughness of hybrid fiber reinforced concrete with low content, and the paper mainly contains the following contexts:(1)According to research results and conventional fiber reinforced concrete flexural toughness evaluation systems, such as ASTM-C1080、JSCE-SF4、RILEM and Regulation of China Association for Engineering Construction Standardization to analyze and summarizethe characteristics and shortcomings of flexural toughness evaluationmethods that arecommonly used at home and abroad.(2)Accordance with the requirements of Standard test methods for fiber reinforced concrete in China,under the situation that the total volume content is 1%, experiments about third-point bending test and notched beam bending test are done for steel fiber reinforce concreteteel fiber and dura fiber hybrid fiber reinforce concrete and steel fiber and plastic fiber hybrid fiber reinforce concrete.And to analyze characteristics of the third-point flexural toughness evaluation system and notched beam flexural toughness evaluation system. Research shows:notched beam flexural toughness evaluation systemis more suitable for the index of flexural touhness, when evaluating concrete flexural toughness with low content hybrid fiber.(3)0n the basis of the notched beam test research,to studythe influence of hybrid fiber on concrete reinforcement and toughness, andto explorethe linear relationship between mid-span deflection and CMOD. Research shows:bending strength of concrete fl、ultimate bending strength fuand energy absorption valueDlf, D2fhas beenimproved by hybrid fiber,and the amplification is between 12% to 44%.The trilinear relation between mid-span deflection and CMOD isestablished.The flexural toughness of hybrid fiber reinforced concrete can be analyzed and evaluated from the angle of mid-span deflection and CMOD.(4)Referring to RILEM standard, calculation of hybrid fiber concrete fracture energy, the influence of hybrid fiber on concrete fracture energy are studied, and the contact equivalent flexural strength feq1、feq2 and fracture energy GF areexplored. Research shows:concrete fracture energyis improved by hybrid fiber, especially steel fiber. The hybrid fiber reinforced concrete beam specimen during bendingcan be analyzed from two angles of the fracture energy and the equivalent flexural strength.