Rheology of Fresh Cement and Concrete: International Conference Proceedings
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A unique procedure for finding the rheological properties of fresh Portland cement concrete using concrete shear tests. Author s : S. Girish, B.
Rheological properties are characterized by flow behavior and are described by Bingham parameters. Based on the measured test results, the storage modulus, G' representing the elastic portion in viscoelastic materials , and the loss modulus, G representing the viscous portion. The strain sweep showed variations in the storage modulus with strain amplitude, which was expected for a flocculated suspension.
The storage modulus, G , was independent of the strain up to 0. This reflects the breakdown of the flocculated network structure as the strain is increased. The product of the modulus and the strain at which breakdown is first observed, i. This static yield stress is not necessarily related to the yield stress under flowing conditions, which is reflected in the Bingham or Herschel-Bulkley yield stresses.
The loss modulus, G'', was smaller than the storage modulus at LVR, indicating a solid-like response, where most of the stress in the system is supported by the solid colloidal network structure.https://europeschool.com.ua/profiles/wijyhume/contactos-gordas-madrid.php
The rheology of fresh cement and concrete - A review — Heriot-Watt University
As the strain amplitude goes beyond the critical value, the loss modulus becomes higher than the storage modulus, which means the behavior changes to a more fluid-like response. Note that the level of G is still significant, and this structure results in a yield stress in steady flow. Based on the results of the strain sweep, the strain amplitude of 0. In Fig.
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As in the strain sweep, the storage modulus in the frequency sweep was higher than the loss modulus in the. Both parameters for the dynamic oscillatory tests were within the LVR and the frequency sweep tests were then performed. The results are shown in Fig. The observations for the storage modulus, G , complement the observations from the steady shear flow results. Several conclusions can be drawn from these measurements:. In the case of FA mixtures, the storage modulus increased slightly with increasing replacement ratios of FA but this was not observed clearly.
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- Rheological behaviour of fresh cement paste as measured by squeeze flow.
On the other hand, the SF mixtures showed a clear difference. The overall variation of the oscillatory shear measurement has a close relationship with the results of the steady shear measurement. Therefore, in this study, a detailed investigation was conducted to determine the relationship between the variation of the storage modulus and yield stress.
The yield stress provides information concerning the microstructure of the sheared suspension. In this experiment, it is the structure that exists as the shear rate is decreased. In dynamic oscillatory shear, the storage modulus and critical strain are related to the fundamental microstructural aspects of the flocculated suspension at rest Schultz and Struble Several studies have shown that systems with G'values independent of frequency also show yield stresses in steady shear flow Lobe and White ; Davis a, b; Ahuja Onogi et al.
They analyzed data on a crosslinked polystyrene latex. While depletion floc-culation was initially described by Asakura and Oosawa , it was not until Heath and Tadros that the depletion effect was connected to gelation and the rheolog-ical measurements of the modulus.
Determination of Bingham Parameters of Fresh Portland Cement Concrete Using Concrete Shear Box
Onogi obtained the yield stress by fitting the non-linearity in their viscosity data with a Casson model, even though their data showed no actual yield point. They obtained G'and G" as functions of frequency, and the data did not display a frequency-independent plateau. They then proposed a relationship between the yield value and the complex stress defined by. Yang et al. Franck reported excellent agreement between the yield stress and the component, G0c0c, where c0c is the critical strain amplitude corresponding to the onset of nonlinear vis-coelastic behavior.
Based on the power law relationship between the yield stress and complex modulus, the following equation is proposed, which is a modified version of the equation proposed by Onogi et al. For the measured results from all mixtures, the relationship between the yield stress and storage shear modulus was. As shown in Fig. The final approximation in Eq. The prefactor, a, in Eq. Moreover, the dynamic oscillatory measurements are much faster to perform than the shear history that needs to be imposed to obtain the yield stress.
Therefore, the measured parameters from the oscillatory shear measurement were utilized to understand the rheological properties. In addition, the viscoelastic properties, which provide information on the microstructure of the sheared suspension should be examined carefully to predict the flow behaviors in a pipe. To understand the flow behavior in a pipe under high pressure, the properties of the lubrication layer between bulk concrete and a pipe wall should be examined. In this study, along with steady shear measurements, oscillatory shear measurements were performed to examine the viscoelastic properties.
The following conclusions were obtained:. Each of the three mixture systems incorporating BSF, FA, and SF displayed different interactions depending on the types and replacement ratios of the mineral admixtures. Through integrating the results from the steady shear and the dynamic oscillatory measurements it was possible to draw conclusions about the types of interactions occurring.
Rheological behaviour of fresh cement paste as measured by squeeze flow
The best correlation between the measured yield stress and the complex modulus followed a power law that is somewhat different in form from the mechanical models that are generally used to relate the yield stress to the modulus. The initial behavior of pumped concrete can be analyzed systematically by examining the viscoelastic properties via oscillatory measurements. This article is distributed under the terms of the Creative Commons Attribution 4. Ahuja, S. Effect of carbon black on the rheological properties of styrene n-butyl methacrylate copolymer melt. Astarita, G. Nicolais Eds.
New York, NY: Springer. Aleekseev, S. On the calculation of resistance in the pipes of concrete pumps. MekhanizatsiyaStroitel'stva, 9 1 , Asakura, S. Interaction between particles suspended in solutions of macromolecules.
Journal of Polymer Science, 33, Atzeni, C. Comparision between rheological models for portland cement pastes. Cement and Concrete Research, 15, Banfill, P. Browne, R. Tests to establish concrete pumpability. Proceedings ACI Journal, 74 5 , Choi, M. Prediction on pipe flow of pumped concrete based on shear-induced particle migration.
Cement and Concrete Research, 52 10 , Lubrication layer properties during concrete pumping. Cement and Concrete Research, 45 3 , Chow, T. The rheological properties of cement slurries: Effects of vibration, hydration conditions, and additives. SPE Production Engineering, 3, Cooke, C. Primary cementing improvement by casing vibration during cement curing time.