Comparative study of the yield stress determination of cement pastes by different methods

摘要

Different methods have been proposed in the literature to determine the yield stress of cement grouts. These methods may present wide differences especially for thixotropic materials such as cement pastes. In this paper, different mixtures of water-cement-superplasticizer were studied for various w/c ratios and superplasticizer dosages. From shear tests of the mixtures in a rheometer, yield stress was determined in different ways: by identification on the experimental flow curve or by modelling flow curve through different rheological models. The conventional rheological models as Bingham model and Herschel-Bulkley model are not in agreement in the majority of the cases studied especially at low shear rates where thixotropy can be observed. In order to enhance the modelling in this area and allows to accurately determine the yield stress, we compared the results obtained through the conventional rheological models to that obtained by a thixotropy model. From the obtained results, it turns out that the latter allows to better predict the behaviour of thixotropic cement grouts and their yield stress.