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Theau Conte, Rachid Bennacer, Mohend Chaouche
Thixotropic behavior of cement paste under large amplitude oscillatory shear

Appl. Rheol. 27:5 (2017) 53914 (9 pages)

Cement-based materials exhibit highly complex rheological properties, in particular yielding and thixotropy. These two properties can be characterized by considering rebuilding under a constant stress (creep) after shear at high rate. The rebuilding kinetics can be considered through the time evolution of the viscoelastic properties. However at the beginning of the rebuilding process the oscillatory behavior may be non-linear since the microstructure is destroyed by the shear flow. In the present investigation the rebuilding kinetics of cement pastes under oscillatory stress is considered through the transition from large amplitude oscillatory shear (LAOS) regime to small amplitude oscillatory shear (SAOS) regime. Three different cement paste mixes are considered: plain cement, nano-clay blended cement paste and cellulose ether blended cement paste. These three mixes are selected in order to deal with qualitatively different rheological properties.

Cite this publication as follows:
Conte T, Bennacer R, Chaouche M: Thixotropic behavior of cement paste under large amplitude oscillatory shear, Appl. Rheol. 27 (2017) 53914.

N. Ouari, A. Kaci, A. Tahakourt, M. Chaouche
Rheological behaviour of fibre suspensions in non-Newtonian fluids

Appl. Rheol. 21:5 (2011) 54801 (10 pages)

The influence of short fibre addition on the rheological behaviour of different non-Newtonian fluids is investigated experimentally. Two types of suspending fluids are considered: power-law shear thinning fluids and yieldstress shear-thinning fluids. The power-law suspending fluids consist of aqueous xanthan solutions at different concentrations. The yield stress fluids are mortar tile adhesives characterised by different rheological parameters. The flow curves of the suspensions at different fibre contents are determined at controlled stresses. Three rheological parameters are inferred from the flow curves: the yield stress, the consistency and the fluidity index. The influence of the fibres on the rheological behaviour of purely shear-thinning fluids is found to be quite similar to what can be expected for Newtonian suspending fluids. On the other hand, addition of fibres to yield stress granular fluids leads to a qualitatively different change of their rheological properties compared to the case of Newtonian suspending fluids. In particular, it is found that the fibres can lead to the decrease of the apparent viscosity and the yield stress for low fibre concentrations in the case of granular suspending fluids. Our experimental findings indicate that the models for fibre suspensions in Newtonian solvents cannot be used straightforwardly in the case of fibre suspensions in granular materials such as building materials, ceramic materials, etc.

Cite this publication as follows:
Ouari N, Kaci A, Tahakourt A, Chaouche M: Rheological behaviour of fibre suspensions in non-Newtonian fluids, Appl. Rheol. 21 (2011) 54801.

Abdelhak Kaci, Rachid Bouras, Mohend Chaouche, Pierre-Antoine Andreani, Herve Brossas
Adhesive and Rheological Properties of Mortar Joints

Appl. Rheol. 19:5 (2009) 51970 (9 pages)

Adhesive properties of fresh mortar joints containing different dosage rates of a water-soluble polymer (cellulose ether based) are investigated using the probe tack test. This test consists of measuring the evolution of the normal force required to separate at a given velocity two plates between which a thin layer of the sample is sandwiched. Three different adhesive components are inferred from the measured stretching force: cohesion, adhesion and adherence. The influence of the polymer dosage rate and the pulling velocity on the evolution of these adhesive properties is investigated. The adhesive components are then related the rheological properties of the mortars which are shown to behave as Herschel-Bulkley shear-thinning fluids.

Cite this publication as follows:
Kaci A, Bouras R, Chaouche M, Andreani P, Brossas H: Adhesive and Rheological Properties of Mortar Joints, Appl. Rheol. 19 (2009) 51970.

A. Kaci, M. Chaouche, P.-A. Andreani, H. Brossas
Rheological behaviour of render mortars

Appl. Rheol. 19:1 (2009) 13794 (8 pages)

Steady state and transient rheological behaviours of a one-coat render mortar are considered experimentally using a shear rheometer equipped with the vane geometry.The flow curves performed at controlled shear-rates exhibit highly pronounced minima, which is attributed to shear localization and strong thixotropy. This latter property is further investigated separately by considering the temporal growth of the apparent stress at very low shear-rate, reflecting the material's microstructure rebuild up following shearing at different high shear rates. It is found that rebuilding characteristic time is roughly independent upon shear history, indicating that this is a material parameter. The influence of water dosage rate on the rheological behaviour is considered. As expected, apparent viscosity and yield stress decrease with increasing kneading water amount. The rebuilding up kinetics is found to be non sensitive to water dosage rate, suggesting that the material's processability would be preserved when changing this parameter, although significant creeping may be expected at high water dosage rates.

Cite this publication as follows:
Kaci A, Chaouche M, Andreani P-A, Brossas H: Rheological behaviour of render mortars, Appl. Rheol. 19 (2009) 13794.

Rachid Bouras, Mohend Chaouche, Salah Kaci
Influence of Viscosity-Modifying Admixtures on the Thixotropic Behaviour of Cement Pastes

Appl. Rheol. 18:4 (2008) 45604 (8 pages)

Water soluble polymers such as cellulosic or starch ethers are often included in the mix-design of Self Compacting Concretes (SCCs) in order to improve their stability and robustness. The stability, including resistance to liquid-solid separation and sedimentation, may be attributed to the increase of the viscosity of the liquid phase due to the thickening effect of the polymer. The later is then referred to as a Viscosity-Modifying Admixture (VMA). In the present study, we consider the influence of VMAs on the rheological properties of the material at cement scale level. In particular, the change in the thixotropic properties of the cement paste due to the inclusion of VMA is investigated. It is found that addition of VMA significantly enhances rebuild-up kinetics at rest following shearing at high shear rate. The influence of VMA on the steady state rheological properties is also considered. As reported in the literature, the yield stress is found to monotonically increase with VMA content, while the consistency presents a minimum indicating the existence of an optimum value of the VMA for which the workability of the cement paste is maximum.

Cite this publication as follows:
Bouras R, Chaouche M, Kaci S: Influence of Viscosity-Modifying Admixtures on the Thixotropic Behaviour of Cement Pastes, Appl. Rheol. 18 (2008) 45604.

T.H. Phan, M. Chaouche
Rheology and stability of self-compacting concrete cement pastes

Appl. Rheol. 15:5 (2005) 336-343

The rheological behaviour of a cement paste used in Self-Compacting Concretes (SCC) formulations is compared to that of an 'ordinary' cement paste (OC) devoid of organic admixtures. In order to mimic the flow conditions experienced by the cement paste in the inter granular space of concretes, the rheological behaviour is investigated in a squeeze flow geometry. By considering the evolution of the squeeze force for different velocities as a function of the instantaneous distance between the discs, it is found that the behaviors of the two cement pastes are qualitatively different. For the OC pastes, the force decreases with increasing squeeze velocity for any given discs separation, indicating that the material is undergoing fluid-solid separation due to filtration of the fluid phase through the porous media made up by the grains. Such behaviour reflects the very poor flowability of the OC paste. The behaviour of the SCC paste is qualitatively different. Above a certain critical value of the speed Uc, the force is an increasing function of the speed for any given disc separation. Under these flow conditions the rheological behaviour of the material is that of a viscous, although highly non-Newtonian, fluid which corresponds to the flowability conditions of the material. For squeeze speeds smaller than Uc, the rheological behaviour of the SCC paste is similar that of OC, indicating that below this critical velocity the material undergoes solid-fluid separation corresponding then to its non-flowability zone.

Cite this publication as follows:
Phan,PH, Chaouche M: Rheology and stability of self-compacting concrete cement pastes, Appl. Rheol. 15 (2005) 336.

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