Rheological requirements for printable concretes

Steady state flow of cement suspensions: A micromechanical state of the art

The capability of processing robust Engineered Cementitious Composites (ECC) materials with consistent mechanical properties is crucial for gaining acceptance of this new construction material in various structural applications. ECC’s tensile strain-hardening behavior and magnitude of tensile strain capacity are closely associated with fiber dispersion uniformity, which determines the fiber bridging strength, complementary energy, critical flaw size and degree of multiple-crack saturation. This study investigates the correlation between the rheological parameters of ECC mortar before adding PVA fibers, dispersion of PVA fibers, and ECC composite tensile properties. The correlation between Marsh cone flow rate and plastic viscosity was established for ECC mortar, justifying the use of the Marsh cone as a simple rheology measurement and control method before fibers are added. An optimal range of Marsh cone flow rate was found that led to improved fiber dispersion uniformity and more consistent tensile strain capacity in the composite. When coupled with the micromechanics based ingredient-tailoring methodology, this rheological control approach serves as an effective ECC fresh property design guide for achieving robust ECC composite hardening properties.

Rheology, fiber dispersion, and robust properties of Engineered Cementitious Composites

https://hal.archives-ouvertes.fr/hal-00542980/document

Cellulose ethers influence on water retention and consistency in cement-based mortars

Rheological properties of ultra-high-performance concrete — An overview

The Marsh Cone: A Test Or a Rheological Apparatus?

Abstract We show that the rheological characteristics of a fresh cement paste can be determined from inclined plane tests. The apparent flow curve measured from inclined plane flows coincides with the apparent rheogram from classical rheometer tests and the flow curve obtained from local Couette flow measurements with magnetic resonance imaging (MRI). In order to describe the thixotropic properties of these fluids we suggest to use a simple model, the four parameters of which may be determined from specific, practical, inclined plane experiments.

Thixotropic Behavior of Fresh Cement Pastes from Inclined Plane Flow Measurements

From MRI measurements we show that in a flowing cement paste thixotropic effects dominate over short time scales while irreversible effects become significant over larger timescales. The steady and transient flows exhibit a yielding behavior which differs from usual yield stress model: the transition from the solid to the liquid regime is abrupt. We propose a simple thixotropic model based on these observations. The validation is done on the steady and transient state on local experimental tests. We build the local rheogram which is representative of the intrinsic rheological properties. Comparisons with apparent rheograms demonstrate that it is possible to use correction techniques from the literature to have access to the real behavior law of the material from standard measurements but that, in the case of the material studied in this paper, this would nevertheless lead to an underestimation of the yield stress.

Modelling thixotropic behavior of fresh cement pastes from MRI measurements

Abstract The grouts are suspensions containing cement used in the technique of prestressing by post-tension. Cement, from its chemical nature, protects the wire ropes (strands) from corrosion. To be able to play correctly this protective role, the grout must remain homogeneous and must entirely cover the strands. The lack of stability of the grouts, which results in packing or sedimentation, is a major problem. In this article, we try to correlate the rheological properties of the grout with its capacity to remain homogeneous. We show that an increase in the concentration of superplasticizer, a polymer solution, decreases the thixotropic behavior of the grout, but on the other hand, increases the effects of sedimentation. We explain this phenomenon by the modification of the structure of a three-dimensional network in relation to the interparticle interactions.

Stability of Cement Grout: Study of Sedimentation Phenomena

The proposed approach consists in studying the behaviour of a concrete starting from four uncoupled suspensions scales: suspending fluid, corresponding to water and the additives, cement paste, mortar and concrete. Rheometric tests using controlled shear rates or shear stresses were carried out on each uncoupled suspension. The experimental data exploitation led us to propose a widened parametric analysis. The influence solid concentration and the particles size on the evolution of the rheological parameters such as the yield stress and the apparent viscosity was identified. In addition, the rheological behaviour of an uncoupled suspension is directly controlled by the behaviour of the uncoupled suspension from size range immediately below.

Rhéologie des suspensions à matrice cimentaire : approche expérimentale multi- échelle

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