Influence of hydroxypropylguars on rheological behavior of cement-based mortars

International audienceHydroxypropylguars (HPGs) are used as water retention agents in modern factory-made mortars. Nevertheless, these molecules can also impact the rheological behavior of cement-based materials. The influence of HPG and its dosage on mortar rheological properties was thus investigated thanks to a suitable measurement procedure. HPG allows keeping a positive yield stress value while the yield stress of hydroxypropyl methyl cellulose (HPMC) mortars was found to decrease with an increase in dosage. HPG increases the shear-thinning behavior and the consistency of mortars. The study of pore solution viscosity suggests that the entanglement of HPG coils beyond a threshold dosage is crucial to understand the rheological macroscopic behavior of HPG-admixed mortars. Nevertheless, the increase in mortar viscosity induced by HPG was lower than expected which reveals additional and specific repulsive forces induced by polysaccharides

Importance of coil-overlapping for the effectiveness of hydroxypropylguars as water retention agent in cement-based mortars

International audienceThis paper is devoted to the role of hydroxypropylguars (HPG) on water retention (WR) capacities of cement-based mortars. WR and pore solution viscosity of mortars formulated with different dosage and kind of HPG were investigated. The results allowed us to rule-out that WR is only governed by pore solution viscosity. A sharp change in slope was observed on the curve WR vs. polymer dosage. This was attributed to the threshold dosage corresponding to the network formation of hydrocolloidal associated HPG molecules in pore solution. Below this dosage, no effect of HPG on WR was obtained. Above this dosage, HPG aggregates may stop the water flow by plugging the porous network of a thin HPG-enriched filter cake at the interface mortar-substrate. This study showed moreover that additional substitution of alkyl chain on HPG improves its effectiveness at low dosage. This was attributed to an enhancement of overlapping

Use of ultrasonic degradation to study the molecular weight influence of polymeric admixtures for mortars

International audienceThe aim of this paper is to provide a methodology to study the influence of the molecular weight of polysaccharidic admixtures on mortar properties. A wide range of admixtures with different molecular weight and constant structure was prepared. This has been made possible by the use of ultrasonic treatment, a simple, effective, and without additive method. It appears that cellulose and guar gum derivatives, used as water retention agents, exhibit a significant molecular weight reduction according to the ultrasonic treatment duration. The water retention capacity of the mortars mixed with ultrasonically degraded admixture solutions increases with molecular weight for a same admixture. However, comparing water retention values obtained with similar molecular weight of a same family shows that effectiveness of polysaccharides as water retention agent is not linearly linked to their molecular weight

Recent Updates to the CFD General Notation System (CGNS)

The CFD General Notation System (CGNS) - a general, portable, and extensible standard for the storage and retrieval of computational fluid dynamics (CFD) analysis data has been in existence for more than a decade (Version 1.0 was released in May 1998). Both structured and unstructured CFD data are covered by the standard, and CGNS can be easily extended to cover any sort of data imaginable, while retaining backward compatibility with existing CGNS data files and software. Although originally designed for CFD, it is readily extendable to any field of computational analysis. In early 2011, CGNS Version 3.1 was released, which added significant capabilities. This paper describes these recent enhancements and highlights the continued usefulness of the CGNS methodology

Influence of hydroxypropylguars on fresh-state properties of cement-based mortars

L’ajout d’adjuvants dans les mortiers permet d’obtenir diverses propriétés selon lesperformances souhaitées. Les polysaccharides sont utilisés pour améliorer la capacité derétention d’eau et le comportement rhéologique du mortier. Cependant, ils engendrent unretard de prise du ciment et représentent un poids économique considérable. Il apparaît doncque la compréhension de l’interaction entre les polysaccharides et le ciment est nécessaire.Etant donné que les comportements sont différents selon le type de polysaccharide, l’étuded’une nouvelle famille de polysaccharides constitue un axe de recherche majeur. Leshydroxypropylguars (HPG) ont été choisis car ils ont été présentés comme de très bonsagents rétenteurs d’eau et sont déjà utilisés industriellement.Il s’avère que les HPG confèrent effectivement aux mortiers d’excellentes propriétés derétention d’eau. Le mécanisme de rétention d’eau est attribué à la formation d’agglomératsqui, au-delà d’une concentration critique, bouchent le réseau poreux à l’interface mortier-substrat.De plus, ces molécules ralentissent nettement la cinétique d’hydratation du cimenten modifiant la croissance des hydrates par adsorption. Les HPG augmentent également la contrainte seuil de cisaillement et la consistance des mortiers. Toutes cespropriétés diffèrent lorsque les HPG sont introduits pré-dissout dans l’eau de gâchée. Uneméthodologie de fragmentation par ultra-sons des polysaccharides a été développée dans lebut d’étudier l’impact de leur masse moléculaire sur les propriétés des mortiers à l’état frais.Sur tous ces aspects, le comportement des HPG a été comparé à celui des éthers de cellulose,adjuvants rétenteur d’eau de référence.Modern factory-made mortars are complex materials, in which are added some kinds of admixtures used to exhibit various properties. Polysaccharides are admixtures used in order to improve water retention capacity and rheological behavior of freshly-mixed mortars.However, polysaccharides induce a delay of cement hydration and represent a large part of mortar raw material cost. The improvement of the knowledge about polysaccharide-cement interaction is therefore necessary. In past, different behaviors were observed according to the kind of polysaccharide. The study of a new polysaccharide family is thus a major way of research. The hydroxypropylguars were chosen since they were presented as promising water retention agents and they are now well-established in the construction industry.Results show that HPG improve the water retention capacity of cement-based mortars. The working mechanism is attributed to the formation of HPG aggregates above a critical dosage, which may stop the water flow by plugging the porous network at the interface mortar-substrate. Moreover, HPG induce a decrease in the hydrates growth rate because of adsorption on the cement hydrated phases, and enhance the consistency and the yield stress of mortars. All these properties are influenced by the pre-dissolution of HPG in the mixing water. A methodology of ultrasonic degradation was also established in order to study the molecular weight influence of polysaccharides on fresh-state properties. Cellulose ethers were systematically investigated as polysaccharidic admixture reference

Influence des hydroxypropylguars sur les propriétés des mortiers de ciment à l’état frais

Modern factory-made mortars are complex materials, in which are added some kinds of admixtures used to exhibit various properties. Polysaccharides are admixtures used in order to improve water retention capacity and rheological behavior of freshly-mixed mortars.However, polysaccharides induce a delay of cement hydration and represent a large part of mortar raw material cost. The improvement of the knowledge about polysaccharide-cement interaction is therefore necessary. In past, different behaviors were observed according to the kind of polysaccharide. The study of a new polysaccharide family is thus a major way of research. The hydroxypropylguars were chosen since they were presented as promising water retention agents and they are now well-established in the construction industry.Results show that HPG improve the water retention capacity of cement-based mortars. The working mechanism is attributed to the formation of HPG aggregates above a critical dosage, which may stop the water flow by plugging the porous network at the interface mortar-substrate. Moreover, HPG induce a decrease in the hydrates growth rate because of adsorption on the cement hydrated phases, and enhance the consistency and the yield stress of mortars. All these properties are influenced by the pre-dissolution of HPG in the mixing water. A methodology of ultrasonic degradation was also established in order to study the molecular weight influence of polysaccharides on fresh-state properties. Cellulose ethers were systematically investigated as polysaccharidic admixture reference.L’ajout d’adjuvants dans les mortiers permet d’obtenir diverses propriétés selon lesperformances souhaitées. Les polysaccharides sont utilisés pour améliorer la capacité derétention d’eau et le comportement rhéologique du mortier. Cependant, ils engendrent unretard de prise du ciment et représentent un poids économique considérable. Il apparaît doncque la compréhension de l’interaction entre les polysaccharides et le ciment est nécessaire.Etant donné que les comportements sont différents selon le type de polysaccharide, l’étuded’une nouvelle famille de polysaccharides constitue un axe de recherche majeur. Leshydroxypropylguars (HPG) ont été choisis car ils ont été présentés comme de très bonsagents rétenteurs d’eau et sont déjà utilisés industriellement.Il s’avère que les HPG confèrent effectivement aux mortiers d’excellentes propriétés derétention d’eau. Le mécanisme de rétention d’eau est attribué à la formation d’agglomératsqui, au-delà d’une concentration critique, bouchent le réseau poreux à l’interface mortier-substrat.De plus, ces molécules ralentissent nettement la cinétique d’hydratation du cimenten modifiant la croissance des hydrates par adsorption. Les HPG augmentent également la contrainte seuil de cisaillement et la consistance des mortiers. Toutes cespropriétés diffèrent lorsque les HPG sont introduits pré-dissout dans l’eau de gâchée. Uneméthodologie de fragmentation par ultra-sons des polysaccharides a été développée dans lebut d’étudier l’impact de leur masse moléculaire sur les propriétés des mortiers à l’état frais.Sur tous ces aspects, le comportement des HPG a été comparé à celui des éthers de cellulose,adjuvants rétenteur d’eau de référence

Influence des hydroxypropylguars sur les propriétés des mortiers de ciment à l'état frais

L ajout d adjuvants dans les mortiers permet d obtenir diverses propriétés selon lesperformances souhaitées. Les polysaccharides sont utilisés pour améliorer la capacité derétention d eau et le comportement rhéologique du mortier. Cependant, ils engendrent unretard de prise du ciment et représentent un poids économique considérable. Il apparaît doncque la compréhension de l interaction entre les polysaccharides et le ciment est nécessaire.Etant donné que les comportements sont différents selon le type de polysaccharide, l étuded une nouvelle famille de polysaccharides constitue un axe de recherche majeur. Leshydroxypropylguars (HPG) ont été choisis car ils ont été présentés comme de très bonsagents rétenteurs d eau et sont déjà utilisés industriellement.Il s avère que les HPG confèrent effectivement aux mortiers d excellentes propriétés derétention d eau. Le mécanisme de rétention d eau est attribué à la formation d agglomératsqui, au-delà d une concentration critique, bouchent le réseau poreux à l interface mortier-substrat.De plus, ces molécules ralentissent nettement la cinétique d hydratation du cimenten modifiant la croissance des hydrates par adsorption. Les HPG augmentent également la contrainte seuil de cisaillement et la consistance des mortiers. Toutes cespropriétés diffèrent lorsque les HPG sont introduits pré-dissout dans l eau de gâchée. Uneméthodologie de fragmentation par ultra-sons des polysaccharides a été développée dans lebut d étudier l impact de leur masse moléculaire sur les propriétés des mortiers à l état frais.Sur tous ces aspects, le comportement des HPG a été comparé à celui des éthers de cellulose,adjuvants rétenteur d eau de référence.Modern factory-made mortars are complex materials, in which are added some kinds of admixtures used to exhibit various properties. Polysaccharides are admixtures used in order to improve water retention capacity and rheological behavior of freshly-mixed mortars.However, polysaccharides induce a delay of cement hydration and represent a large part of mortar raw material cost. The improvement of the knowledge about polysaccharide-cement interaction is therefore necessary. In past, different behaviors were observed according to the kind of polysaccharide. The study of a new polysaccharide family is thus a major way of research. The hydroxypropylguars were chosen since they were presented as promising water retention agents and they are now well-established in the construction industry.Results show that HPG improve the water retention capacity of cement-based mortars. The working mechanism is attributed to the formation of HPG aggregates above a critical dosage, which may stop the water flow by plugging the porous network at the interface mortar-substrate. Moreover, HPG induce a decrease in the hydrates growth rate because of adsorption on the cement hydrated phases, and enhance the consistency and the yield stress of mortars. All these properties are influenced by the pre-dissolution of HPG in the mixing water. A methodology of ultrasonic degradation was also established in order to study the molecular weight influence of polysaccharides on fresh-state properties. Cellulose ethers were systematically investigated as polysaccharidic admixture reference.ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF