Use of creep recovery protocol to measure static yield stress and structural rebuilding of fresh cement pastes

In this study, a creep recovery shear rheological protocol was applied to fresh cement pastes. A viscosity bifurcation behavior was observed through applying a range of creep stresses. When applied stress is sufficiently low viscosity increases and the material yields, exhibiting viscoelastic solid-like behavior. Beyond a critical stress viscosity decreases and the material flows, exhibiting viscoelastic liquid-like behavior. Through examining this bifurcation behavior we found that the transition of viscosity occurs at very low strains. The strains at which this transition occurred were compared with critical strains measured through low amplitude oscillatory shear. Results provided support that the solid-liquid transition occurs beyond the critical stress measured through creep, thereby tying it to static yield stress. The protocol was implemented to probe pastes modified with attapulgite clays, a highly thixotropic system, and was found to be effective in characterizing static yield stress and thixotropic rebuilding.