Effect of pre–shearing regimes on rheological parameters of cement paste

Abstract

In rheological testing, different test regimes can result in large differences in the rheological curves, and the pre‐shear procedure is one of the most important parts of the test. In order to investigate the effect of the pre‐shear regime on the rheological properties of cement pastes, an Anton Paar 102 rotary rheometer was used for the test. Two different pre‐shear regimes (RF and CP pre‐shear), three different pre‐shear duration times (50 s, 100 s, 150 s), and four different pre‐shear rates (25 s−1, 50 s−1, 100 s−1) are carried out for the test. The results showed that with the increase of pre‐shear duration or rate, the four rheological parameters (plastic viscosity, yield stress, rheological index, and thixotropy) of the pastes decrease in different degrees. RF pre‐shear was more influenced by shear time, while CP pre‐shear was influenced by shear time and rate. The pre‐shear regimes led to different changes in the flocculation structure of the cement paste, which had a great influence on rheological parameters ultimately. Based on the improved Krieger‐Dougherty model, the effective solid volume fraction of cement paste was calculated. Analysis shows that the phenomenon of “deflocculation” and “re‐flocculation” occurs when the cement paste is subjected to shear action, thus, the pre‐shear regimes destroy the structure of the pastes. With the increase of pre‐shear duration or rate, the effective volume fraction decreased, which indicated that the initial flocculation structure was broken. The greater the damage degree of pre‐shear, the slower the establishment rate of the internal structure of the pastes in dynamic shear, resulting in lower rheological parameters.