Study of fresh concrete flow curves

Abstract

Two constants - plastic viscosity and upper yield point obtained by extrapolation from measurements at high speeds of shear in rotation viscometer - are often considered as sufficient to describe fresh concrete rheological behaviour. In the present work the investigation has been expanded to include tests at low shear velocities and at lower yield point because of a practical significance in concrete technology. Tests have shown that three shapes of fresh concrete flow curves appear, which display characteristic shear thinning along the transition from the area of low shear velocities to the area of high shear velocities. Shear thinning or thickening in the region of higher rotation speeds are characteristic for some mixes. The phenomena of shear thickening and thinning can partly be explained as being due to dilatancy and to the related changes in the fluid phase to pore air ratio in fresh concrete. Simple shear static tests have shown that fresh concrete dilatancy is proportional to the square of shear stress. © 1980.