Cracking behavior of steel fiber reinforced concrete revealed by means of acoustic emission and ultrasonic wave propagation

Van Hauwaert, A Delannay, Francis [UCL] Thimus, Jean-François [UCL]

An experimental study on the cracking behavior of steel reinforced concrete (SFRC) is reported. Third-point bend tests were carried out on notched beams. Test setup enabled recording of load bean deflection, and crack mouth opening displacement. Simultaneously, acoustic waves caused by cracking were counted. At regular time intervals, ultrasonic compression waves were induced at one beam end and recorded at the other beam end after propagation through the sample. Both methods reveal the cracking behavior of SFRC. A frequency analysis of the acoustic activity reveals that low-frequency events can be attributed to microcracking, while high-frequency emissions unveil macroscopic happenings such as macrocracks, load transfer from matrix to fibers, and fiber pullout. The ultrasonic waves can be interpreted from their energy or velocity The wave energy is affected by microcracking, while the wave velocity exhibits a change when a macrocrack has developed over a certain beam depth. The conjunction of both methods helps to determine, in an objective manner, the moment when the first macrocrack appears.