Optimization of superplasticizer dosage for cementitious suspension involved in high shear applications – A point of view

The dosage of superplasticizer ( SP) plays a vital role in influencing the behaviour of fresh concrete through cementitious paste. For optimizing the SP dosage, generally empirical tests like mini-slump and Marsh cone are adopted. However, they do not capture the requirement of suitable SP dosage for processes involving high shear energy like pumping. Recent studies have shown that SP, especially polycarboxylate ether/esters (PCE)-based, influences the shear thickening behaviour of cement-based pastes. The addition of PCE at higher dosage, decreases the apparent viscosity by de-flocculation of cement paste. However, at increased shear forces, the reaggregation results in early onset of shear thickening and also increases its intensity, thus affecting the pumping process. On the other hand, the commercially available, site-specific PCE and the prescriptive SP dosages complicate the problem. The above problem necessitates the need to understand the mechanism behind the action of PCE on shear thickening of cement pastes experiencing high shear energy process. In this regard, it is rational to optimize the SP dosage based on shear rates (corresponding to applications) through rheological studies rather than empirical tests.