Rheological study of Portland cement pastes modified with superabsorbent polymer and nanosilica

Abstract

This paper addresses the use of rotational rheometry in determining the rheological parameters (viscosity and yield stress) of cement pastes over time. This study employed Portland cement pastes modified with superabsorbent polymer (SAP) and nanosilica (NS). Nine pastes were tested: one reference paste, two pastes with different amounts of SAP, two pastes with different amounts of NS, and four hybrid mixtures. Flow tests were performed using a parallel plate geometry in a rotational rheometer to determine the viscosity by graphical results and yield stress via the Herschel–Bulkley model. The results show that the flow test is satisfactory for determining the rheological properties, primarily the viscosity. Statistical analysis was performed to quantify the effect of each random variable and their interactions on the rheological properties, providing graphical tools for analyzing the tendencies of the viscosity and yield stress for both additives (SAP and NS). SAP exerted a weak effect on the rheological properties; in contrast, NS caused large changes in both rheological parameters (viscosity and yield stress) in the tested pastes. For pastes containing 2% NS, the presence of SAP caused slight reductions (less than 10%) in the rheological parameters, casting doubt on the absorption of SAP when in contact with mineral additives.