Acoustic emission and ultrasonic pulse velocity of concrete

Both acoustic emission and ultrasonic pulse velocity measurements were used to try to monitor the structural integrity of concrete. Specimens in the form of 150 mm cubes were loaded monotonically to failure, and acoustic emission and ultrasonic pulse velocity were measured simultaneously. Four different concrete mixes were each tested at ages up to two years to provide a wide range of concrete strengths. The results indicated that ultrasonic pulse velocity measurements began to show internal cracking at stresses of about 33 to 66% of the ultimate stress; this method therefore appeared to be more sensitive to damage than acoustic emissions, which indicated severe cracking only at about 80 to 90% of the ultimate stress. However, both ultrasonic pulse velocity and acoustic emission seemed to be affected by the age of the concrete. It was concluded that, for acoustic emission to be used as a reliable indicator of concrete damage, extensive work would have to be done to establish a standard test procedure.