Development and Stabilization of Hybrid Structure of Asphaltene and Graphene

Petroleum and its derivatives, such as bitumen, are complex colloidal system. Their chemical behavior is influenced by various internal and external factors. Adding graphene derivatives to this system will only increase its complexity, thus it must be carefully considered to ensure successful integration. In this thesis, we examine the challenges of introducing graphene derivatives into bitumen and focus on three key questions: a) phase stability of graphene derivatives in bitumen, b) interaction between graphene and asphaltene aggregates, and c) an environmentally friendly and optimal method to modify graphene derivatives for improved bitumen properties. We use various characterization techniques to answer these questions and find that the best strategy for introducing graphene derivatives into bitumen is non-covalently functionalized graphene using the Molecular Wedging method (MW-graphene). The MW-graphene is compatible with asphaltene aggregates and stabilizes in bitumen through mutual interaction. The use of MW-graphene improves the mechanical stability of asphaltene aggregates in bitumen

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

Modification of cement hydration at early ages by natural and heated wood

International audienceHeat treatments of wood are widely used for the reduction of wood swelling and dimensional instability of wood-cement composites. The effect of natural and heated wood on the hydration of cement at early ages was investigated by isothermal calorimetry, thermogravimetry (TGA) and Fourier transform infrared (FTIR) spectroscopy. The addition of wood strongly delays and inhibits the hydration of the silicate phases. Consequently, the amount of portlandite is lower in composites than in neat cement. Approximately 30% of the inhibition of portlandite precipitation is due to an increase of calcium carbonate content in cement paste. The absorption of a part of water by wood produces a decrease in gypsum consumption. Nevertheless, the ettringite formation is not significantly affected since a diffusion of sulfate ions from wood occurs

Thermo-gravimetric analysis as a tool for the optimisation of wood heat treatment parameters

9 pagesRetification is a heat treatment that decreases the swelling of wood and increases its resistance to fungal attack. It consists in a mild pyrolysis of wood (180°C-260°C) that takes place in a non oxidative atmosphere (nitrogen). The industrial development of retification requires optimisation of the treatment temperature and duration. In order to enhance the homogeneity of temperature in the furnace, and to avoid exothermic reaction, low temperatures seem to be preferable to high temperature. On the contrary, duration and temperature of treatment have to be high enough to provide good biological resistance and stabilization to the wood. However, high temperatures lead to a loss of mechanical strength. A question arises from these previous observations: is there any equivalence between a treatment of short time carried out at high temperature and a treatment of longer time at lower temperature? Answering this question can help to optimise rétification temperature and duration. The purpose of this study is to evaluate the relevance of a “time temperature equivalence” (TTE) for wood pyrolysis in the temperature range of retification. The principle of TTE is adapted from the study of wood viscoelastic properties. In this study, it is applied to the rate of anhydrous weight loss during wood pyrolysis. Thermo-gravimetric analysis (TGA) were performed on maritime pine (Pinus pinaster Ait.-) and beech (Fagus sylvatica) wood powder. Isothermal degradations were carried out at different temperatures ranging from 160°C to 260°C. A specific data analyse was carried out on the TGA derivative (DTG) in order to assess the relevance of the TTE in the temperature range of retification. It gave interpretable results for maritime pine, but not for beech. It showed that for maritime pine wood the TTE is confirmed from 200°C to 220°C, and not confirmed for temperatures superior to 230°C. An optimization of the temperature and time of treatment is thus possible

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