Ceramics-Silikáty

To clarify the influence of shear history and testing protocol on the rheological characterization of cement paste, two representative dynamic shear protocols, namely linear dynamic shear testing (LDST) and stepwise dynamic shear testing (SDST), were applied under varying maximum shear rates. The shear stress–time and shear stress-shear rate responses were analyzed to evaluate the dynamic yield stress, plastic viscosity, and thixotropy of cement paste. The results show that both protocols exhibit generally consistent rheological evolution characterized by typical hysteresis behavior, indicating good comparability between the two dynamic shear methods. However, the measured rheological parameters exhibit different sensitivities to shear history. The dynamic yield stress shows noticeable dependence on the preset maximum shear rate and shear protocol, suggesting that it should be regarded as a shear-history-dependent apparent parameter rather than an intrinsic material constant. In contrast, the plastic viscosity obtained from the Herschel-Bulkley model remains relatively insensitive to the shear path, indicating good robustness of viscosity characterization under different dynamic loading modes. The thixotropic loop area increases significantly with increasing maximum shear rate and exhibits a regime-dependent response to the shear protocol. The essential difference between LDST and SDST lies in the structural evolution process during dynamic shearing. LDST emphasizes continuous structural disruption under non-equilibrium conditions, whereas SDST allows partial structural adjustment during discrete shear stages. The findings suggest that caution should be exercised when directly comparing dynamic yield stress values obtained using different rheological procedures and provide guidance for selecting appropriate dynamic shear protocols for cement-based materials.