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Synopsis Using a set-up in which the bowl of a two-point workability test apparatus was mounted on an electro-magnetic vibrating table, measurements were made on unvibrated fresh concrete and on the same samples under vibration. It was shown that when vibration is applied the flow properties of fresh concrete are no longer represented by the simple linear Bingham model but approximate to those of a power law pseudoplastic with zero yield value. At very low shear rates behaviour approximates to that of a Newtonian fluid and, subject to the exceeding of a small threshold condition, fluidity decreases as a simple exponential function of the maximum velocity of vibration.

Synopsis Apparatus has been developed to measure the flow curve of concretes of medium to high workability. An impeller in the form of an interrupted helix is rotated uniaxially in the concrete by means of a hydraulic transmission and the torque is determined from measurement of the oil pressure. The flow curves conform closely to the Bingham model and, by suitable calibration, it is possible to express values of yield stress and plastic viscosity in fundamental units.

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Using an apparatus in which fresh concrete is allowed to flow out of a vertical pipe while being vibrated, it is confirmed that under vibration and at low shear rates the material behaves as a Newtonian liquid. Effectiveness of vibration is to be assessed in terms of maximum velocity but there is a threshold amplitude below which, and an upper limiting frequency above which, vibration has no effect. It is shown that fluidity determined by this method correlates with fluidity determined earlier by an entirely different method.