Experimental Investigation and Modeling of Early-Age Cement Paste Rheology Using a Controlled Shear-Cycling Protocol

Abstract

Early-age cement paste exhibits continuous changes in rheological behavior due to the combined effects of shear, hydration, and time. Conventional rheological tests often include rest periods or stepped shear changes, which can promote thixotropic rebuilding and hide hydration-driven effects. The purpose of this study is to develop a controlled shear-cycling protocol to limit rest-induced structural recovery and maintain a comparable shear history during early-age testing. Cement pastes with w/c of 0.40, 0.45, 0.50, and 0.55 were tested over the first 30 min after mixing using repeated high-shear disruption to maintain a controlled and comparable structural state, followed by short low-shear measurement intervals. Shear stress was observed as a function of shear rate, w/c, and elapsed time under conditions where the paste structure was repeatedly disrupted. A normalized stress index (NSI) was introduced to quantify short-time stress changes during the low-shear phase. Despite suppression of structural rebuilding, shear stress increased progressively for all mixtures, indicating an irreversible contribution from hydration. Most NSI values remained near zero or became negative, confirming that thixotropic recovery did not control stress evolution. Rheological trends are further supported by microstructural observations. A time-regime-based modeling framework was developed without assuming constant rheological parameters. These results are significant to practical processes, including mixing, pumping, placement, and extrusion, where early-age flow control is critical. © 2026 The American Ceramic Society.