Saint-Quentin-Fallavier, France
Saint-Quentin-Fallavier, France

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Kaci A.,Cergy-Pontoise University | Chaouche M.,Ecole Normale Superieure de Cachan | Andreani P.-A.,Center Dinnovation Of Parexlanko
Cement and Concrete Research | Year: 2011

Fine mineral additives are often used in the formulation of ready-mix mortars as thickeners and thixotropic agents. Yet, these attributed fresh state properties are not clearly defined from the rheological point of view. In the present study, we consider the influence of bentonite (montmorillonite-based clay mineral) on the rheological behaviour of mortars, including in particular creep and thixotropy. The mortar pastes are subjected to different shear-rates and then allowed to creep under fixed shear stresses until reaching steady state, which corresponds to either rest if the applied stress is smaller than the yield stress or permanent flow otherwise. The evolution of the creep strain is investigated depending on shear history for different contents of bentonite. The microstructure rebuilding kinetics after shear (thixotropy) is considered by analysing the temporal evolution of the creep strain for different applied shear stresses (lower than the yield stress). As expected, bentonite is found to enhance the mortar creep (or sag) resistance. This enhancement consists of both an increase of the yield stress recovered after shear, and a diminution of the characteristic time for yield stress recovery (related to microstructure rebuilding). © 2011 Elsevier Ltd.

Kaci A.,Ecole Normale Superieure de Cachan | Bouras R.,Ecole Normale Superieure de Cachan | Phan V.T.,Ecole Normale Superieure de Cachan | Andreani P.A.,Center Dinnovation Of Parexlanko | And 2 more authors.
Cement and Concrete Composites | Year: 2011

Adhesive properties of fibre-reinforced joint mortars in fresh state are investigated using the probe tack test. This test consists of measuring the force required to separate at a given velocity two plates between which a thin layer of the tested material is inserted. The adhesive properties of the mortars, including cohesion and adherence to the plate surface, are inferred from the curves representing the evolution of the tack force versus instantaneous plate separation for different pulling velocities. The adhesive properties are qualitatively related to the rheological behaviour of the mortars. The latter are shown to behave as Herschel-Bulkley shear-thinning fluids. The influence of fibre content on both adhesive and rheological properties is investigated. © 2010 Elsevier Ltd. All rights reserved.

Cappellari M.,Ecole Normale Superieure de Cachan | Cappellari M.,Center Dinnovation Of Parexlanko | Daubresse A.,Center Dinnovation Of Parexlanko | Chaouche M.,Ecole Normale Superieure de Cachan
Construction and Building Materials | Year: 2013

In this study, we consider the influence of different types of polymer thickening admixtures on the rheological behavior of render mortars. The admixtures considered include cellulose-ethers with different molecular weights, a guar ether, and a starch ether. A thorough rheological investigation is performed, including the characterization of the steady state flow behavior and the microstructure at rest. The latter is examined through measuring linear viscoelastic properties using oscillatory rheology. First, it is shown that the fresh mortars behave generally as Hershel-Bulkley fluids with a non-trivial evolution of the rheological parameters with admixture content. The evolution of the viscoelastic properties with admixture content shows that the cellulose ethers and guar ethers decrease the gel-like response of the mortars, while starch ether increases their gel feature. This indicates that there should be a profound difference between the two types of admixtures regarding their organization within the pore solution and their interactions with the mineral particles. The rheological properties are discussed in relation to water retention. It is shown that the ratio between dissipation and elasticity (or cohesion) correlates well with water retention. The more the admixture introduces viscous dissipation (as compared to cohesion) into the system, the more it increases its water retention capacity. Water retention is also correlated with air-entrainment, indicating that the surfactant property of the admixture is a contributing factor. © 2012 Elsevier Ltd. All rights reserved.

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