Surface Relaxivity of Cement Hydrates
Numerous aspects of the physical chemistry of colloidal systems are conditioned by the solid–liquid interface, and this is also the case for hydrated cement systems. Estimating the surface area is thus essential for studying the kinetics of cement hydration and admixture adsorption. Proton nuclear magnetic resonance (NMR) relaxation techniques have already proven useful for this objective, but, for hydrating cements at early ages, it is necessary to know the surface relaxivities of all of the individual phases present to correctly interpret the relaxation data. This paper reports the results of a comparison of NMR relaxometry and Brunauer–Emmett–Teller gas adsorption measurements on various…
Vieillissement environnemental accéléré et propriétés mécaniques des fibres issues du chanvre
International audience; Ce travail a pour objectif de caractériser l’influence d’un vieillissement environnemental accéléré sur les propriétés mécaniques de fibres extra-xylémiennes issues du chanvre. Le protocole de vieillissement accéléré proposé dans cette étude consiste en des cycles de 24h comprenant une phase d’immersion de 12h dans une eau distillée à 70°C et une phase de séchage de 12h dans une étuve contrôlée à 50°C. Les résultats montrent une perte de masse significative et une diminution des propriétés de rigidité et de résistance en traction de l’ordre de 50% après 30 cycles de vieillissement.
Undecylenic acid: A tunable bio-based synthon for materials applications
International audience; An undecylenic acid-based monoglyceride prepared from glycidol and undecylenic acid is used as suitable and tunable synthon for polymerization applications. Epoxidation and acrylation reactions lead to photopolymerizable monomers while transesterification with dimethyl carbonate, metathesis and aminolysis reactions provide access to polyhydroxyurethane-based materials. The successive intermediates were synthesized according to a green chemistry approach implicating solvent-less and catalyzed reactions, and were at each step fully characterized by infrared, 1H and 13C{1H} NMR spectroscopy, elemental analysis and mass spectrometry. Analyses of the resulting polymer mat…
Facile and efficient chemical functionalization of aliphatic polyesters by cross metathesis
International audience; An effective preparation of new tailor-made macromolecular materials via a combination of two (atom-efficient) catalytic transformations is reported. First, new aliphatic polyesters with alternated composition have been prepared using a salen aluminum catalyst system. Next, the pendant vinyl moieties in those copolymers have been selectively transformed into various functional groups by metathesis in the presence of homogeneous Grubbs catalysts. The latter metathesis reaction has been optimized in terms of catalytic activity and selectivity, to define the conditions for an effective and safe procedure that does not affect the macromolecular architecture. All polymer …
Design and development of 100 % bio-based high-grade hemp/epoxy composites
International audience; In order to develop 100% bio-based high-grade epoxy composites, in this study, bio-based epoxy thermosets and hemp slivers are processed and characterized by different technologies. Epoxy resins are synthesized from the diglycidylether of Eugenol, extracted from cloves. They are cured with bio-based acid anhydrides. The physicochemical properties of the resulting epoxy resins are characterized using thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and nanoindentation. The mechanical properties of hemp fibres extracted from the slivers are also determined using tensile tests. After their processing and characterization, these bio-based consti…
Early C3A hydration in the presence of different kinds of calcium sulfate.
International audience; Hydration reactions of C3A with various amounts of calcium sulfate hemihydrate, gypsum or a mixture of two, were investigated by isothermal microcalorimetry, and a monitoring of the ionic concentrations of diluted suspensions. This study shows that sulfate type used modifies the early C3A-CaSO4 hydration products and the rate of this hydration. The fast initial AFm formation observed before ettringite precipitation in the C3A-gypsum system is avoided as soon as hemihydrate is present in the suspension. This was attributed to.higher super saturation degrees and then higher nucleation frequency with regard to the ettringite obtained in the presence of hemihydrate. More…
Design and synthesis of biobased epoxy thermosets from biorenewable resources
International audience; Biobased diepoxy synthons derived from isoeugenol, eugenol or resorcinol (DGE-isoEu, DGE-Eu and DGER, respectively) have been used as epoxy monomers in replacement of the diglycidyl ether of bisphenol A (DGEBA). Their curing with six different biobased anhydride hardeners leads to fully biobased epoxy thermosets. These materials exhibit interesting thermal and mechanical properties comparable to those obtained with conventional petrosourced DGEBA-based epoxy resins cured in similar conditions. In particular, a high Tg in the range of 90–130 °C and instantaneous moduli higher than 4.3 GPa have been recorded. These good performances are very encouraging, making these n…
Modification of the rate of formation and surface area of ettringite by polycarboxylate ether superplasticizers during early C3A–CaSO4 hydration
Abstract Early C3A–CaSO4 hydration was studied in the presence of various amounts of two polycarboxylate ether superplasticizers differing in their grafting degree. Hydration and surface area developments were investigated by in-situ NMR relaxometry coupled with BET and DSC during the first 2 h after mixing. This study enables a quantitative comparison of the amount and the specific surface area of the ettringite precipitated along the C3A–CaSO4 hydration with or without PCE. The main effect of PCE is to strongly increase ettringite specific area for a variable period. These effects are clearly dependent on the PCE charge and dosage and are reduced when using delayed addition. In this conte…
Development and characterization of a bio-based epoxy matrix for high-grade bio-based composites
This study aims to develop 100% bio-based hemp/epoxy composites for semi-structural and structural applications. The thermal and mechanical performances of a 100% bio-based matrix derived from biomassare evaluated and reveal properties in the same order of magnitude as those obtained for polyepoxides based on DGEBA, that means a glass transition temperature of approximately 150°C and mechanical properties in the order of 120MPa for the maximum stress and 3.2 GPa for the tangent apparent modulus. This natural origin matrix is then used for the manufacture of composites reinforced with hemp rovings. The bending properties of these 100% bio-based materials are equivalent to those determined fo…
Biomass-derived phenylpropenes as precursors of thermosetting epoxy resins : from synthesis to materials
International audience; As demonstrated by the current international awareness, and supported by several independent studies, the replacement of fossil fuels and the need to find competitive alternatives are crucial issues to reduce global warming, and to limit the consequences for life on Earth [1]. As part of this challenge, the biomass and molecules from the living can be considered as providential pools of renewable building blocks dedicated to the chemistry of the future. This is particularly true in polymer science, where the use of renewable resources for the synthesis of fully or partially biobased materials arouses a great deal of interest, in academia and industry [2].
Fluidizing efficiency of comb-like superplasticizers: The effect of the anionic function, the side chain length and the grafting degree
Superplasticizers and especially polycarboxylate grafted polyethylene oxide (PCE) demonstrated their efficiency to fluidify concrete. The aim of this work is to investigate the evolution of the fluidity as a function of adsorption in a sulfated solution with a wide variety of comb-like superplasticizers and at incomplete adsorption rate. Polymers with various side chain lengths, grafting ratios and also with modified anionic functions (carboxylate, dicarboxylate and phosphate) were synthesized. Inert calcite suspensions were used to mimic early age cementitious materials avoiding the cement hydration. Models of polymer conformation and yield stress prediction have been tested. But the most …
Towards Fully Bio-Based Thermosets: From Prepolymers Synthesis to Composite Applications
International audience
Changes in Cement Paste and Mortar Fluidity after mixing induced by PCP: A parametric study
International audience; The interaction mechanism between polycarboxylate-type superplasticizer (PCP) and cement hydration is not fully understood and incompatibilities between concrete and additive are sometimes observed. In some cases, the fluidity tends to increase (“overfluidification”) few minutes after mixing. This is a problem because the overfluidification leds to bleeding of the concrete which could be critical on job site. Our study consisted first in highlighting the phenomenon of “over-fluidification” by slump flow tests on mortar. Next, the time evolution of the rheological behaviour of cement pastes in the presence of PCP was analysed thanks to a rheometry protocol in order to…
New reactive isoeugenol based phosphate flame retardant : toward green epoxy resins
A biobased reactive phosphate flame retardant derived from isoeugenol was synthesized and fully characterized (1H, 13C, 31P NMR, FTIR, MS) with the aim of improving flame retardancy behavior of bio...
Development and characterization of a bio-based epoxy matrix for high-grade bio-based composites
This study aims to develop 100% bio-based hemp/epoxy composites for semi-structural and structural applications. The thermal and mechanical performances of a 100% bio-based matrix derived from biomassare evaluated and reveal properties in the same order of magnitude as those obtained for polyepoxides based on DGEBA, that means a glass transition temperature of approximately 150°C and mechanical properties in the order of 120MPa for the maximum stress and 3.2 GPa for the tangent apparent modulus. This natural origin matrix is then used for the manufacture of composites reinforced with hemp rovings. The bending properties of these 100% bio-based materials are equivalent to those determined fo…
Étude d'un procédé de traitement innovant des fibres de chanvre sous condition de fluide supercritique et propriétés induites
International audience
Tailoring the anionic function and the side chains of comb-like superplasticizers to improve their adsorption
Nowadays admixtures and especially superplasticizers are unavoidable components of the concrete formulation. The high fluidizing efficiency of the comb-like superplasticizers must not overshadow their high costs. This study aims to determine the PCE structure parameters which influence their adsorption in order to enhance their resistance to sulfate competitive adsorption and thus minimize their dosage. The PCE adsorption has been studied on calcite and ettringite which are both surfaces representative of early hydrating cement. The effect of the POE side chain length and density and also of the PCE anionic function i.e. carboxylate, dicarboxylate or phosphate on the adsorption has been ana…
Influence of three types of superplasticizers on tricalciumaluminate hydration in presence of gypsum.
International audience; Different types of superplasticizers have been widely used over the past few decades in order to produce a more fluid or very high strength and durable concrete. These chemical admixtures interfere with the various physico-chemical processes occurring in early cement paste. In this paper we present results from a study on the influence of superplasticizers on pure tricalciumaluminate hydration in presence of gypsum. The suspensions hydration has been investigated by conductimetry, isothermal calorimetry and total organic carbon analysis of the liquid phase. The time taken for ettringite formation has been determined without superplasticizer and in presence of three d…
Crystal structure of the diglycidyl ether of eugenol
The diepoxy monomer (DGE-Eu) was synthesized from eugenol by a three-step reaction. It consists of a 1,2,4-trisubstituted benzene ring substituted by diglycidyl ether, a methoxy group and a methyloxirane group. The three-membered oxirane rings are inclined to the benzene ring by 61.0 (3) and 27.9 (3)°. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming layers parallel to the ab plane.