Abstract
The emergence of new special concretes on construction sites has shown that concretes of the same slump may behave quite differently on the job. For these concretes, one cannot rely on the traditional workability tests for quality control and rheological characterization. It has been claimed that the flow behavior of fresh concrete closely approximates the Bingham model and that at least two parameters are therefore needed to describe its rheology. Thus, rheological measurements must be carried out at not fewer than two shear rates. This study examines the applicability of the Bingham model to fluid and self-leveling highstrength concrete (HSC). Results obtained from a rheometer are compared with results of the standard slump test. Fluid concrete mixtures were investigated that had a water/binder ratio (w/b) of 0.33 and slump values of 200 ± 20 mm and incorporated proportions of limestone filler, silica fume, and ground silica as partial replacement (by volume) of cement. In addition, self-leveling concrete mixtures (torque viscosity ≤ 1 Nm at 15 min) having a w/b ratio of 0.25 and 15 percent replacement of cement by various fillers were examined. The possibility of characterizing the rheology of fluid and self-leveling HSC on the basis of only two tests carried out at two different shear rates was addressed. An effort was made to define which is more relevant in a rheometer flow curve: the ascending part, the descending part, the maximum stress requirement, the flow resistance, the torque viscosity, or combinations of these factors. The possibility of measuring the rapid stiffening behavior of fresh HSC with time and the effect of ultrafine particles on the rheology using rheometric tests were also investigated.
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