Abstract
The rheological properties of fresh cement paste are highly influenced by a large number of parameters, among which the most important factors are the applied shear stress, and the shear history, the age of the sample and the temperature. The effects of these parameters on the yield stress (designated as structural limit stress in this work), the viscosity and the structural recovery rate (i.e., the change in dynamic viscosity with time at rest) were studied. In parallel, the changes in ion composition of the carrier liquid, mineral phase content and granulometry were investigated. The results reveal that all investigated rheological parameters exhibit an approximated bi-linear trend with respect to the degree of hydration, with a period of quasi-constant properties until a degree of hydration of approximately 0.07, followed by a non-linear increase. This increase could be attributed to the formation of calcium hydroxide (CH) and calcium-silicate-hydrate (C-S-H) via calorimetry results. With regard to the effect of the shear history of the sample on the rheological properties, the structural limit stress showed a minor dependency on the shear history immediately after the end of shearing, which, however, vanished within the first minute at rest. The same is true for the structural recovery rate. The presented results give detailed insights into the influences of hydration and shear on the rheological properties—especially the thixotropy—of fresh cement pastes.
Highlights
The control of the rheological properties of fresh concrete during casting is essential for the production of high-quality concrete structures
This effect occurs at hydration stages, which are not relevant for rheology, the results reveal that sulphate depletion depends on temperature, since the associated peak is shifted to later hydration stages with decreasing temperature
The total heat after 96 h in the case of the 30 ◦ C samples is used to calculate the degree of hydration assuming that these samples are completely reacted, despite the fact that this values is not reached in practice
Summary
The control of the rheological properties of fresh concrete during casting is essential for the production of high-quality concrete structures. The rheological properties of fresh concrete are subject to a great variety of influencing factors. Among the most important are the age of the concrete (time after water addition), the shear history—i.e., the shear the concrete was previously exposed to, e.g., due to mixing, transport and placement—and the temperature (see, e.g., [1]). All of these influencing factors primarily act on the interaction behavior. The investigations in this paper are carried out on fresh cement paste, which allows for a much more detailed study of the underlying processes
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