Testing of Rheological Properties of Concrete Mixtures Using a Special Vibroviscometer

The rheological properties of concrete mixtures are presently important when new technologies for transporting, handling, placing, and compacting concrete are used in new concrete construction technologies. A new methodology and equipment, the remolding type viscometer, was developed for testing the rheological properties of concrete mixtures. During the vibration, the flowing time of the concrete mixture from an inner cylinder to a cylindrical vessel with different pressure is measured and the rheological characteristics, the yield stresses and viscosity, are calculated according to the developed equations. By using this equipment the rheological behaviors of concrete mixtures (thixotropy and dilatancy) can be analyzed. This testing methodology can be used to optimize the proportions of different concrete mixtures addressing factors such as aggregate granulometry, admixtures dosage optimization, and other considerations. Experiments were conducted with vibrated concrete mixtures having sand content from 50 to 75% in the aggregate mixture. The yield stresses, viscosity, and dilatancy of concrete mixtures were calculated according to the abovementioned testing methodology. The tests revealed that the rheological curves of the concrete mixture are not linear as in Bingham’s model but have a curved shape. Increasing the sand content in the aggregate from 50 to 65% increases the yield stress of concrete mixture approximately 1.5 times and afterward remains constant. The lowest viscosity and highest workability is obtained with the sand content in the aggregate ranging between 50 and 65%. The lowest values of dilatancy index were obtained with the sand content in the aggregate ranging within 50–65%.