Title : SPECIFIC FEATURES OF CEMENTITIOUS MATERIALS AT LOW AND HIGH FLOW RATES IN PRESENCE OF SUPERPLASTICIZERS
Authors : Pascal Boustingorry, Ph.D
Publication : 8 - 10, October 2015
Volume : 1
Pages :
Price : 250
Abstract : Cementitious suspensions all feature common flow characteristics when their flow curve is observed. A minimum in stress is observed towards low shear rates which also corresponds to a transition towards heterogeneous flow. A minimum of viscosity often appears towards high shear rates, beyond which the suspension enters a shear-thickening regime the origin of which remains unclear. In between these two limits of shear rate, the expected shear-thinning behaviour takes place, where apparent viscosity may be linked to a shear-rate-dependent degree of suspension flocculation. The low shear rate limit behavior seems to be related to the competition between flocculation by cement hydration and deflocculation by shear, the latter being influenced by superplasticizers. The high shear rate limit may be interpreted as shear-induced reflocculation. But a close look at data shows that a rise of normal forces is observed in the shear-thickening regime, hinting at a frictional mechanism, and that different superplasticizer technologies do not respond identically. All these phenomena may be of huge importance as far as concrete self-placing or pumping are concerned.