Ultrasonic pulse velocity
Measurement of ultrasonic pulse velocity (UPV) is a means of assessing variations in the apparent strength of concrete. UPV equipment is also used for detecting the presence of voids, honeycombing or other discontinuities. The velocity of a pulse of ultrasonic energy in concrete is influenced by the elastic stiffness and mechanical strength of the concrete.
The equipment consists of two transducers, usually in the form of metal cylindrical heads, one of which is used to transmit an ultrasonic pulse and the other is a receiver. They are brought into contact with the concrete surface (‘coupled’) using a gel or grease. They are connected by cable to a control box which contains a pulse generator, timing circuit and digital display. The digital display indicates the time for the ultrasonic pulse to travel between the transmitting and receiving transducers. As in the case of the rebound hammer, it is possible to develop an empirical relationship between pulse velocity and strength but this relationship is influenced by type of cement, type and size of aggregate, presence of reinforcement, moisture condition, compaction and age of concrete.