Study on early ultrasonic characteristics of cemented paste backfill

The ultrasonic properties of cemented paste backfill are measured during 48 hours after mixing, and the ultrasonic wave velocity, frequency spectrum and first-wave amplitude are analyzed, which provides a reference for testing the early strength formation and initial setting of the cemented paste backfill.The ultrasonic wave velocity measured after transmitting cemented paste backfill indicated that the wave velocity increases with the curing time, but the growth rate of ultrasonic wave velocity reduces with the increase of binder contents during 1 000 min.The ultrasonic wave velocity is stable and then it increases quickly and suddenly with the increase of curing time and binder contents, which confirms that the change of ultrasonic wave velocity and curing time curve could reflect the level of hydration reaction.According to the frequency spectrum analysis, the process of hydration reaction is smooth and steady for the specimen with three percent of binder contents, but it is dramatic change with seven percent of binder contents from 1 250 min to 2 000 min.The frequency spectrum is found to become gathered with curing time and it increases with binder contents.Based on the analysis of the first-wave amplitude, the first-wave amplitude is found to increase with curing time.But the amplitudes of ultrasonic waves are similar for pastes with different binder contents at the same curing time which indicates that the first-wave amplitude isn’t sensitive to binder contents.