Fabienne Farcas

Molecular weight distribution of asphaltic paving binders from phase-angle measurements

Based on previous works on polymers and regular bitumens, a new method for determining the molecular weight distribution (MWD) of asphaltic paving binders, using the phase angle () of the complex modulus measured in the linear viscoelastic domain, has been developed in this paper. MWDs of pure petroleum bitumens, natural bitumens, modified bitumens and artificially aged bitumens are calculated by this method and compared with MWDs obtained by gel permeation chromatography. The two methods give comparable results, but the δ-method developed here is more sensitive to the molecular weight of species. This method is very simple to implement, and seems a powerful tool in the determination of MWD of bitumens, in the visualisation and repartition of modifiers in the bitumen matrix and in the ageing monitoring and quantification.

Ageing Performances of Asphaltite Modified Bitumens; Comparisons with Equivalent Petroleum Bitumens

This work focuses on the ageing behavior of asphaltite modified paving bitumens. The addition of asphaltites in soft petroleum bitumens gives harder binders which are suitable for the production of high modulus bituminous mixes used in pavements construction. Such techniques are already used in several projects. However it is not known how asphaltite modified binders behave during ageing. In general, bitumens get harder, more elastic and consequently more brittle during ageing. In order to evaluate the ageing incidence we have studied the evolution of several mechanical properties of asphaltite modified bitumens during ageing. The evolutions of asphaltite modified bitumens during aging are compared with the evolutions of pure petroleum bitumens of equivalent grade. The petroleum bitumens of equivalent grade, used for comparison purposes, are produced in refinery in France by the same fabricant as the soft petroleum bitumen which has been selected to be modified by asphaltites. All the petroleum bitumens satisfy the European Norms and are used currently in France and elsewhere. The present study shows that the asphaltite modification gives hard paving binders which have better performances, regarding to the ageing evolution, compared to hard petroleum bitumens produced in refinery. The asphaltite appears to be an ageing inhibitor.

Influence of binder on the multiscale properties of hemp concretes

Abstract Biobased materials are increasingly being used for building insulation. Hemp concrete is an efficient thermal insulation material containing renewable resources, providing living comfort thanks to its acoustical and hygrothermal properties. In this study, two hemp concrete ‘wall’ formulations are manufactured with the same type of hemp shiv and two commercial binders: natural cement and a lime-based formulated binder. Ninety days of curing (65% RH – 20 °C) ensure the hardening of the materials. Mortars are made up simultaneously to control the behaviour of the binders. The influence of binders on functional properties of hemp concretes and the relation with their microstructure are investigated in this article. The two materials exhibit similar thermal conductivity, acoustic performances and hydric properties, linked to their similarities considering density, open porosity, air resistivity, specific surface area and pore size. However, several other parameters describing the microstructure of the concretes are different depending on the binder, such as interparticle porosity, intra-porosity and tortuosity. Both formulations have low compressive strength compared with hemp concretes analysed in other studies. In our case, hydration of binders does not appear to occur. This could be due to an impact of the shiv extractible compounds on the hydration of the mineral binders.

Bitumen Emulsion Destabilization Kinetics: Importance of the Crystallized Wax Content

We study the kinetics of bitumen emulsion destabilization after the addition of sodium hydroxide (NaOH) using macroscopic observations and rheology. Destabilization occurs in a two-step process: first, emulsion flocculates, forming a percolated network of contacting drops, and then coalescence provokes the irreversible connection of bitumen drops, leading to a bitumen continuous network that further relaxes the shape. We show that the destabilization kinetics exhibits a rheological easily identifiable signature allowing reproducible and accurate measurement of the connection/coalescence time trc (which corresponds to the time, determined by rheology, required to form the network made of drops connected by nonrelaxed coalescence). Using this powerful tool, we show that, even if viscosity is thought to govern the shape relaxation of the connected network it does not determine the connection kinetics. Indeed, emulsions with similar rheological behaviors exhibit very different destabilization times. Instead, we evidence a good correlation between the bitumen crystallized wax content and trc. From these experimental results, we discuss the stabilizing effect against coalescence of crystals in bitumen emulsions.

Modeling the linear viscoelastic behavior of asphaltite-modified bitumens

A modeling approach which allows predicting the linear viscoelastic behavior of bitumen blends from the linear viscoelastic properties of individual constituents is presented in this paper. This approach consists in a combination of the Tsenoglou rule for miscible viscoelastic materials with the Palierne model for viscoelastic emulsions. Based on some simple assumptions, this combination predicts satisfactorily the rheological behavior of asphaltite-modified bitumens and, consequently, it can be used for dosage purposes. Beyond asphaltite-modified bitumens, the modeling approach developed here can be applied on reclaimed asphalt-modified bitumens, polymer-modified bitumens, and on blends of partially miscible polymers presenting a suspended droplet morphology.

Bitumen-in-water emulsion: Destabilization by electrolyte solutions and rheological evaluation

The breaking process of the bitumen emulsion is initiated when put into contact with aggregates during the mixing step. It is due to interactions between the binder and the aggregates and also water loss (evaporation and gravity flow). Some mechanisms are supposed to play a role in the breaking process which highly rules the coating quality of the aggregates by the bitumen binder, the implementation step of the mixture on the pavement and the final mechanical properties of the mixture. However the bitumen emulsion breaking process is not fully understood. It remains difficult to know which parameters have a preponderant role on emulsion breaking and how the kinetics of the different involved phenomena impact the global destabilization. The first part of the presented paper aims to determine the influence of electrolyte solutions, used as emulsion destabilizing agents to simulate ionic species release in the aqueous phase of the emulsion by the aggregates, on concentrated oil-in-water bitumen emulsion stability. Secondly, the evolution of rheological properties of the emulsion during destabilization process, which have been put in evidence in the first part, will be presented and discussed The emulsion destabilization, which included a gelation process, has been evaluated by macroscopic and microscopic observations, as well as size distribution and rheological measurements. An interpretation of the destabilization processes will be drawn using rheology, the emulsion formulation and the electrolyte solutions.

Study of UV rays effects on the evolution of bituminous mix behaviour

During their lifetime, asphalt layers are subjected to aging. Recently, attentions have been paid to the laboratory ageing tests with UV radiation applied to the bituminous binders but there are few studies dealing with the photo-oxidation of binders in a bituminous mix. So, the aim of this study was to investigate whether the influence of ultraviolet light on bitumen ageing might be assessed in the bituminous mixes using an experimental apparatus dedicated to the ageing of paint. The results show that the influence of UV radiation on the ageing of bituminous mixes containing an elastomer modified bitumen cannot be totally ignored: compared with thermal aging, the UV impact can be found to be dominant for the production of carbonyl functions, the disappearance of C=C double bond of SBS and the increase of binder’s hardening. This study has highlighted, on the one hand, that inside the bituminous mix, the UV radiations do increase the rate of oxidation and, on the other hand, that the evolution’s kinetics due to a pure thermal oxidation or a photo-oxidation processes are different. Consequently, the UV exposure may affect the bitumen’s properties of pavement upper layers more strongly than the laboratory test (without UV action) does.