Modification of water retention and rheological properties of fresh state cement-based mortars by guar gum derivatives

International audienceThe present study examines the influence of chemical composition and structure of guar gum derivatives on water retention capacity (WR) and rheological behavior of fresh state cement-based mortars. The investigation was also completed by adsorption isotherms. For this, original guar gum, three HydroxyPropyl Guars (HPG) and two hydrophobically modified HPGs were selected. The effect of the molar substitution (MSHP) and of hydrophobic substitution (DSAC) was investigated. The results highlight that chemical composition of HPGs has a remarkable effect on fresh state properties of mortars. The original guar gum does not impact on neither WR nor rheological behavior. Increasing MSHP leads to an improvement of the WR and the stability of mortars while the hydrophobic units further enhance WR and lead to a decrease in the yield stress and an increase in the resistance to the flow of admixed mortars

Effect of Guar Gum Derivatives on Fresh State Properties of Portland Cement-Based Mortars

International audienceMortars are traditionally made from a mixture of sand, a binder and water. However, modern factory-made mortars are currently, very complex materials. Indeed, to exhibit various properties from the fresh paste to the hardened material, mortar formulations are composed of many mineral and organic admixtures. Among organic admixtures, polysaccharides are widely used in mortar formulation to improve water retention capacity of the freshly-mixed materials. The water retention capacity is an essential property of mortars to enhance cement hydration and its adhesion to a substrate. Moreover, many polysaccharide admixtures, acting as viscosity-enhancing agents, prevent segregation and improve the homogeneity and workability of cement-based system. Indeed, the viscosity of the system strongly increases using polysaccharides. Nevertheless, polysaccharides, as sugars, act on cement hydration. The main drawback is the retarding effect in hydration mechanism and setting-time of the cement.The aim of this study is to focus on the effect of guar gum derivatives on fresh state properties of Portland cement-based mortars, such as water retention, rheological behavior and the hydration delay. This work focuses on the guar gum derivatives since their manufacturing process is low pollutant and they provide very good properties to cement-based mortars. The results highlight that the chemical composition of guar gum derivatives (MS, DS, additional alkyl chain) are the key levers to improve water retention of mortars and to adapt the rheological behavior of the cementitious paste to a specific application

Single Molecule Analysis Research Tool (SMART): An Integrated Approach for Analyzing Single Molecule Data

Single molecule studies have expanded rapidly over the past decade and have the ability to provide an unprecedented level of understanding of biological systems. A common challenge upon introduction of novel, data-rich approaches is the management, processing, and analysis of the complex data sets that are generated. We provide a standardized approach for analyzing these data in the freely available software package SMART: Single Molecule Analysis Research Tool. SMART provides a format for organizing and easily accessing single molecule data, a general hidden Markov modeling algorithm for fitting an array of possible models specified by the user, a standardized data structure and graphical user interfaces to streamline the analysis and visualization of data. This approach guides experimental design, facilitating acquisition of the maximal information from single molecule experiments. SMART also provides a standardized format to allow dissemination of single molecule data and transparency in the analysis of reported data

Carbohydrate-derived ionic liquids : Exploring the chiral pool for novel reaction media

The exploration of Chiral Ionic Liquids (CILs) have expanded exponentially over the last five years, and the increasing number of new CILs published so far, displaying either chiral anion or chiral cation, gives good reason for the recent reviews reporting their synthesis and applications [1]. CILs have been designed to act as stereoselective solvents in asymmetric synthesis, as chiral phase in gas chromatography, as shift reagents and chiral selectors in the determination of enantiomeric composition of pharmaceutical drugs. The synthesis of many CILs exploits the asymmetry already present in the chiral pool, especially in natural aminoacids or \uf061-hydroxy acids. However, no ILs based on natural carbohydrates have been reported so far. Carbohydrates are among the most abundant, low-cost natural sources of chiral material. Moreover, their manipulation has widely developed over more than one century, so that the protection and derivatization of natural monosaccharides can be easily performed through largely applied standard reactions. These considerations prompted us to design the synthesis and characterization of carbohydrate-based ionic liquids as new chiral solvents. Due to the presence of many hydroxyls, these CILs are provided of high coordination ability that can be tuned by varying the electronic density of their oxygens through a proper protecting group pattern. Therefore, carbohydrate-based ILs could be used as coordinating solvents in stereoselective and/or metal-catalysed reactions and, in principle, they could be used as shift reagents. We synthesized compounds 1-3 as the first carbohydrate-based ILs, starting from commercially available methyl-\uf061-D-glucopyranoside [2]. As these new CILs were supposed to act as solvents in organic reactions, they had to be stable in common reaction conditions. For this reason, the reactivity of hydroxyls was considerably lowered by protection as methyl ethers, and the labile anomeric acetal was reduced to an inert methylene group. ILs 1-3 were prepared following a common synthetic approach through a four-step procedure, and they were fully characterised in their physico-chemical properties. They represent the first terms of a new class of chiral solvents from low-cost natural sources

GLUCOSE-DERIVED IONIC LIQUIDS: EXPLORING LOW-COST SOURCES FOR NOVEL CHIRAL SOLVENTS

The exploration of Chiral Ionic Liquids (CILs) have expanded exponentially over the last five years, and the increasing number of new CILs published so far, displaying either chiral anion or chiral cation, gives good reason for the recent reviews reporting their synthesis and applications.1 CILs have been designed to act as stereoselective solvents in asymmetric synthesis, as chiral phase in gas chromatography, as shift reagents and chiral selectors in the determination of enantiomeric composition of pharmaceutical drugs. The synthesis of many CILs exploits the asymmetry already present in the chiral pool, especially in natural aminoacids or \uf061-hydroxy acids. However, no ILs based on natural carbohydrates have been reported so far. Carbohydrates are among the most abundant, low-cost natural sources of chiral material. Moreover, their manipulation has widely developed over more than one century, so that the protection and derivatization of natural monosaccharides can be easily performed through largely applied standard reactions. These considerations prompted us to design the synthesis and characterization of carbohydrate-based ionic liquids as new chiral solvents. Due to the presence of many hydroxyls, these CILs are provided of high coordination ability that can be tuned by varying the electronic density of their oxygens through a proper protecting group pattern. Therefore, carbohydrate-based ILs could be used as coordinating solvents in stereoselective and/or metal-catalysed reactions and, in principle, they could be used as shift reagents. We synthesized compounds 1-3 as the first carbohydrate-based ILs, starting from commercially available methyl-\uf061-D-glucopyranoside. As these new CILs were supposed to act as solvents in organic reactions, they had to be stable in common reaction conditions. For this reason, the reactivity of hydroxyls was considerably lowered by protection as methyl ethers, and the labile anomeric acetal was reduced to an inert methylene group. ILs 1-3 were prepared following a common synthetic approach through a four-step procedure, and they were fully characterised in their physico-chemical properties. They represent the first terms of a new class of chiral solvents from low-cost natural sources