Investigation on flexural toughness evaluation method of steel fiber reinforced lightweight aggregate concrete

The main purpose of this paper was to investigate the influence of steel fiber (SF) content on the flexural properties of steel fiber reinforced lightweight aggregate concrete (SFLWC) and propose a suitable method for evaluating flexural toughness. At the first step, the effects of SF content on the basic properties, including workability, density and compressive strength were investigated. Additionally, the microstructure of SFLWC was also observed by using scanning electron microscope (SEM). A slight change was made for Deng's proposed toughness index which could reflect the degree to which the fiber improves the post-cracking toughness of plain concrete. A simple and practical method for evaluating the flexural toughness of fiber reinforced concrete was recommended by JG/T 472-2015 standard, which solved many problems in the existing methods. This method makes full use of pre-peak and post-peak information which can reflect the influence of fiber on the pre-peak and post-peak behaviors. The results revealed that SF had a negative impact on the workability and density of lightweight aggregate concrete (LWC). However, the addition of SF could improve the compressive strength of LWC to some extent. The optimal SF content of 2.0% was proposed based on the degree to which the fiber improved the toughness of plain LWC. SF addition could significantly enhance the equivalent initial flexural strength and the equivalent residual flexural strength of LWC. The effectiveness of SF on pre-peak behavior was superior to that on the post-peak behavior. The interfacial transition zone between aggregates and paste was not the weakest link in SFLWC.