Determination of Bingham Parameters of Fresh Portland Cement Concrete Using Concrete Shear Box

The workability of fresh concrete should be characterized by its rheological properties based on material science approach to overcome the inadequacies of traditional empirical tests like slump test. Generally the rheological properties of fresh concrete are described by Bingham parameters in terms of two physical quantities, namely yield stress and plastic viscosity. Rheometers are used to find the two rheological parameters, which use high speed torque to shear the concrete and the stimulus provided during testing is dynamic. But, there is no concurrence in the measurement of rheological values by various rheometers. In this systematic study the Bingham parameters of normal concrete was found from using a specially fabricated new concrete shear box. The advantage of this test is the low shear rate applied on the specimen during testing which is similar to the condition the fresh concrete experiences in the field and the static condition of the test. The procedure is unique in that, after finding the peak shear stress, shear stress at zero normal stress and at zero displacement were found and finally finding the Bingham parameters. The water was varied from 160 to 190 l /m3 and cement content from 300 to 450 kg/m3. Different displacement rates (5 to 25 mm/min) and normal stresses (0.015 to 0.035 N/mm2) were used. Total number of tests considered was 324 and the mixes were prepared with and without Superplasticizer. The results show that the concrete shear box can be used as a new tool to measure the relative values of yield stress and plastic viscosity of fresh concrete effectively as a static test, with low shear rate. The values are higher but the trends are very similar to the studies using rheometers.