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

An experimental study on the cracking behavior of steel reinforced concrete (SFRC) is reported. Third-point bend tests were carried out on notched bea ms. Test setup enabled recording of load bean deflection, and crack mouth o pening displacement. Simultaneously, acoustic waves caused by cracking were counted. At regular time intervals, ultrasonic compression waves were indu ced at one beam end and recorded at the other beam end after propagation th rough the sample. Both methods reveal the cracking behavior of SFRC. A freq uency analysis of the acoustic activity reveals that low-frequency events c an be attributed to microcracking, while high-frequency emissions unveil ma croscopic happenings such as macrocracks, load transfer from matrix to fibe rs, and fiber pullout. The ultrasonic waves can be interpreted from their e nergy or velocity The wave energy is affected by microcracking, while the w ave velocity exhibits a change when a macrocrack has developed over a certa in beam depth. The conjunction of both methods helps to determine, in an ob jective manner, the moment when the first macrocrack appears.