| Popis: |
Abstract The setting behavior of concrete mixtures can be indirectly monitored by the penetration resistance test given by ASTM C 403. Arbitrary values of penetration resistance are associated to the initial and final set times. This test is carried out on the previously sieved mortar portion of the concrete mixture, which makes its practical use rare. Alternatively, ultrasound testing can be used to characterize this transition period, since the propagation of ultrasonic waves is greatly affected by the formation of cement hydration products and the extent of microstructure development. In this research, the propagation of ultrasonic waves in fresh concrete during the setting period was studied. In addition to the ultrasonic pulse velocity (UPV), other ultrasonic parameters such as group velocity, parameters related to ultrasonic energy and frequency were monitored during the setting period of various concrete mixes. It was observed that as setting progressed, there was a greater ease of ultrasonic transmission with a continuous increase of wave amplitudes. The results indicated that a combined analysis of the time domain parameters of UPV, group velocity and the time that 10% of energy has propagated (t10) could be used to improve the characterization of the microstructure development regarding the setting behavior of concrete mixtures. |
