Toughness test and acoustic emission characteristics analysis of fiber reinforced concrete

Aiming at the problems of building cracking and damage caused by underground mining, a concrete material with strong deformation resistance is developed. The compressive, splitting, axial compressive and four-point bending tests of fiber reinforced concrete(FRC) with five different fibers including hooked steel fiber, wave-shaped steel fiber, microfilament copper-plated steel fiber, imitation steel fiber and filamentous polypropylene fiber are carried out. The variation rules of compressive toughness evaluation index and flexural toughness evaluation index of FRC are studied. The initiation and propagation of cracks in the wave-shaped fiber reinforced concrete during four-point bending are monitored through acoustic emission test. The mechanical behavior of FRC in the whole bending failure stage is analyzed by combining acoustic emission related parameters with the bending toughness of concrete. Based on the existing evaluation methods of concrete's bending toughness, a new bending toughness evaluation method is proposed containing five new flexural toughness indexes. This method can quantitatively analyze the pre-peak and post-peak bending properties of fiber reinforced concrete. According to the experimental results, it can be concluded that the microfilament copper-plated steel fiber has the greatest improvement on the compressive toughness of concrete and can effectively inhibit the cracking and spalling of concrete. The hooked steel fiber and wave-shaped steel fiber have the greatest improvement on the flexural toughness of C40 and C50 concrete and change the crack growth mode. The addition of fiber reduces the crack width and the generation of early microcracks, prolongs the crack propagation time, and the transformation from tensile crack to shear crack is the main reason for the improvement of FRC toughness and the irregular rise of cracks. Acoustic emission characteristic parameters can accurately monitor the characteristic points of crack initiation stage, stable growth stage, unstable cracking stage, residual failure stage and the characteristic points of particular deflection value. The improved evaluation method of bending toughness can more intuitively reflect the bending performance of FRC.