Etude des phénomènes physico-chimiques à l'interface émulsion de bitume/substrat minéral - Application à la formulation de Bétons Bitumineux à l'Emulsion (BBE)

This PhD thesis contributed to better understand the mechanisms involved at the bitumen emulsion/mineral substrate interface with the aim of controlling the manufacture of bitumen emulsion cold mixtures. The first step of this work was to propose and to implement the pavement design of bitumen emulsion cold-mix wearing courses. After a parametric study involving the emulsion, the mineral components (aggregates and/or Reclaimed Asphalt Pavements) and the mix (residual binder content, total water content), cold mixtures were manufactured in laboratory and in worksite in order to stress the impact of scaling on the mixture properties. The mechanical characteristics of the mixtures were quite satisfactory. Meanwhile, the results pointed out the importance of adopting a more rigorous method to identify the bitumen emulsion/mineral substrate interface. The second step of this work was to study this interface at three levels. The first level concerns the analysis of the mineral substrate in contact with the acid from the emulsion using rise in pH tests and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). These trials allowed showing discrepancies in chemical reactivity due to the petrographic nature of the mineral substrate and quantifying the ion release in aqueous solution. The second level is focused on the characterisation of the interactions between emulsifier and aggregates usingelectrophoretic mobility studies. The results showed the emulsifier coverage onto the substrate and differences in substrate coverage as a function of the emulsifier type. The third level is dedicated to the characterisation of the bitumen emulsion wetting and adhesion onto the substrate using sessile drop tests. The experiments performed underlined the influence of the surface state of the substrate on wetting, but do not show clearly the effect of the nature of the emulsion on wetting. Finally, empirical tests used to characterise emulsion breaking, coating and adhesivity have been compared to rise in pH tests, electrophoretic mobility tests, and sessile drop tests.Cette thèse a contribué à mieux cerner les mécanismes à l'interface émulsion de bitume/substrat en vue de maîtriser la fabrication d'enrobés à l'émulsion. La première étape de ce travail a consisté à proposer et à mettre en oeuvre une méthode de formulation de Bétons Bitumineux à l'Emulsion, utilisés en couche de roulement. Après une étude paramétrique sur l'émulsion, les constituants minéraux (granulats et/ou agrégats d'enrobés) et le mélange (teneurs en liant résiduel et eau totale), des matériaux à l'émulsion ont été fabriqués en laboratoire et sur site réel, notamment afin de rendre compte de l'influence du changement d'échelle. Les propriétés mécaniques des matériaux fabriqués ont été très satisfaisantes. Néanmoins, les résultats ont souligné l'intérêt d'adopter une démarche plus scientifique dans la caractérisation de l'interface émulsion de bitume/substrat. La seconde étape du travail a donc été l'étude de cette interface selon trois axes. Le premier axe concerne l'analyse du contact acide de l'émulsion/substrat via des essais de remontée de pH et de spectroscopie d'émission atomique. Ces tests ont permis de montrer des différences de réactivité chimique selon la nature pétrographique du granulat et de quantifier le relargage d'ions en milieu aqueux. Le second axe est focalisé sur la caractérisation de l'interaction émulsifiant/granulats par mesure de mobilité électrophorétique. Les résultats ont démontré lerecouvrement d'émulsifiant sur le substrat minéral et une différence du recouvrement en surface selon la nature de l'émulsifiant. Le troisième axe est concentré sur la caractérisation du mouillage et de l'adhésion de l'émulsion sur le substrat au moyen d'essais d'angles de contact. Les essais réalisés ont mis en évidence l'influence de l'état de surface du substrat sur le mouillage, mais ne montrent pas clairement l'effet de la nature de l'émulsion sur ce mouillage. Enfin des essais empiriques de rupture, d'enrobage et d'adhésivité d'émulsion ont pu être comparés aux essais de remontée de pH, de mobilité électrophorétique et d'angles de contact

Bitumen extraction and recovery in road industry: A global methodology in solvent substitution from a comprehensive review

International audienc

Effects of surfactants on the formulation, cohesion build-up and moisture resistance of virgin and recycled cold bituminous mixtures and relationship to emulsion breakup

The use of bitumen emulsion in pavement structures, coupled with the introduction of reclaimed asphalt pavement (RAP), is an effective approach to preserve non-renewable resources and save energy. The formulation of virgin and recycled cold mix asphalt (CMA) requires the compatibility of the emulsion with the aggregates and RAP, according to their respective physicochemical characteristics. The objective of this research was to investigate the influence of parameters related to the bitumen emulsion and asphalt mixture composition on the implementation and durability of virgin and recycled CMA. The study focused on granite-based CMA with recycling rates of 0 and 50 %. Six emulsions were produced by varying the nature and content of the surfactant (0.9, 1.2 and 1.5 wt%). The mixtures were fabricated with different total water contents. The cohesion build-up and the compressive strength of the optimized mixtures were assessed. The results showed that the optimal total water content of virgin and recycled CMA differed with the surfactant type and decreased when the surfactant content increased, regardless of the composition. Likewise, the kinetics of cohesion build-up of mixtures is influenced by the amount of added water, surfactant nature and content. The moisture resistance of the mixtures is related to their short-term cohesion and is the highest at an optimum emulsifier content. Finally, the recycled asphalt mixes exhibited better compaction properties, higher mechanical strength (+ 0.5-0.7 MPa) and water resistance than those of virgin asphalt mixes

“Towards a better assessment of recycling agent effects on bitumen during hot recycling”

International audienceThe current challenge is to produce asphalt mixtures incorporating higher rates (>50%) of Re-claimed Asphalt (RA) while controlling the quality of the final mix. During the service life of a pavement properties change, mainly due to oxidation and need to be restored. The resulting mix must exhibit at least equivalent performances regarding the mechanical and durability properties compared to that from a mix without RA. Hence, recycling agents are sometimes employed to “rejuvenate” aged bitumen. In this study, three recycling agents were used on both RA and neat bitumens, displaying different compositions. The effects on unaged and aged blends were as-sessed through rheology tests using Dynamic Shear (DSR) and Bending Beam (BBR) Rheome-ters. Data from DSR obtained with 4mm and 8mm parallel plates allowed to calculate the Glov-er-Rowe criteria and to determine the crossover parameters whilst BBR measurements yield Tm, Ts and ΔTc parameters. The blends resulting from the two bitumens displayed a similar evolu-tion of behavior. This outcome suggests that these tests cannot discriminate the origin of the re-juvenation phenomenon since they only highlight the softening effect of the recycling agent and not its impact at the molecular level, i.e. on asphaltene and maltene compounds

Formulation of cold recycled asphalt mixtures: a microscopic scale study of bitumen emulsion wetting on virgin aggregates and reclaimed asphalt pavement (RAP)

International audienceThe cold recycling of bituminous materials recovered from pavements, also called Reclaimed Asphalt Pavement (RAP), presents both economic and environmental advantages. This technique allows the use of bitumen emulsion. At present, there is no rational formulation method for emulsion mixtures and their numerous applications in road pavement remain the expertise of constructors.Recycling with bitumen emulsion raises questions about the interactions of emulsion both with the virgin aggregates and RAP. These two types of materials have very different physicochemical properties. If current knowledge has enabled description of interactions between emulsion and virgin aggregates according to their physicochemical property, those with RAP, aggregates covered with aged binder, remain to be clearly determined. The adsorption process of surfactants on the RAP material, which conditions emulsion wetting and new binder adhesion, should be clarified according to its hydrophobic nature and low reactivity.The main objective of this study is to determine emulsion breaking mechanism on RAP, in comparison with virgin aggregates, whose physicochemical compositions were known. For this purpose, the experimental protocol consisted of conducting surface tension and contact angle measurements on six emulsions, varying the emulsifier nature and content, on polished substrates of diorite and granite and on aggregates coated with an aged binder film extracted from RAP which were exposed to traffic and environmental conditions for several years. The results showed an increase in the surface tensions of emulsions formulated, comparatively to those of aqueous phases from which they were prepared. However, a slight influence of emulsifier nature and content was observed between the surface tension values of the six emulsions tested. The contact angle values of emulsions with RAP are higher than those obtained with the virgin aggregates, whatever the emulsifier nature and content. This indicates the hydrophobic nature of RAP, even though the presence of water inside bitumen emulsions