Monitoring of the mechanical behavior of concrete with chemically treated steel fibers by acoustic emission

Abstract Inclusion of steel fibers is an effective way to increase the ductility of concrete. In order to achieve optimal mechanical properties and especially toughness, chemical treatment of the fibers is applied. Suitable agents improve the bonding between the stiff fiber and matrix enabling more efficient stress transfer. In the present study specimens with plain and chemically treated steel fibers are subjected to four-point bending with concurrent monitoring of their acoustic emission (AE) activity. Specific AE parameters demonstrate that coating offers distinct characteristics to the interphase especially after the maximum load has been reached. Parameters like average frequency (AF) and the rise angle of the waveforms, which are used for cracking mode classification, indicate that the post peak behavior of specimens with chemically treated fibers is more closely related to matrix cracking, while untreated exhibit clear shear behavior due to pull-out. It is concluded that coating effectively contributes to the deflection of the cracks from the fiber–matrix interphase into the concrete matrix. AE analysis sheds light into the fracturing behavior of concrete in real time, in a way that is not possible by any other conventional measurement.