Ultrasonic transmission to monitor setting and hardening of fly ash concrete

Nondestructive ultrasonic transmission measurements were used to measure high cement replacement levels by fly ash's effects on concrete's microstructural development. There was comparison of two different devices, respectively equipped with an ultrasound impactor and ultrasound generator. In all mixtures, but at different rates, ultrasonic pulse velocity changed from 200 to 500 m/s (660 to 1,640 ft/s) to 4,000 to 5,000 m/s (13,100 to 16,400 ft/s). The point, which a solid percolation threshold could correspond with, where a sharp increase started in pulse velocity amounted respectively to 2, 3, 7.5, and 9 hours for the reference mixtures and the 10%, 40% and 60% fly ash mixtures. There was variation between 20 hours for the reference and 56 hours for the 60% fly ash mixture for the age of approach for the asymptotic maximum velocity value. Also, mixture composition made pulse energy change dependent on it. When final pulse velocity value was reached, there was maximum semi-adiabatic temperature change. For the 40 and 60% fly ash mixtures, there was significantly lower compressive strength than for reference and 10% fly ash mixtures.