Investigations of binder rejuvenation related to asphalt recycling

University dissertation from Stockholm : Byggvetenskap

Abstract: Investigations described in this doctoral thesis concernmaterial behaviour related to asphalt recycling. More indetail, the thesis describes development and application ofmethods for characterisation of the rejuvenation process, inwhich old and new binders are mixed. The thesis also includes astate-of-the-art report on asphalt recycling focusing onmaterial-related aspects.As the rejuvenation process involves diffusion of bituminousbinders, a method for measuring rate of diffusion based onFTIR-ATR (Fourier Transform Infrared Spectroscopy by AttenuatedTotal Reflectance) was developed. The method was employed forstudying influence of parameters such as temperature, size andshape of the diffusing molecules as well as the viscosity ofthe medium in which the diffusion takes place. Well-definedsubstances, referred to as markers, were used in some of theseinvestigations. By aid of the FTIR-ATR method, influence ofdegree of binder ageing on the rate of diffusion was analysed.Diffusion in bituminous binders was also characterised byrheological measurements. Finally, knowledge on structuralstability of recycled binders was obtained by solubilitystudies using turbidimetric titrations and three differenttitrants showing widely different solubility parameters(iso-octane, isooctanol and methyl-ethyl-ketone).The literature review shows that there are numerouspublications related to asphalt recycling, but fewinvestigations can be characterised as fundamental, whichillustrates the complexity of the research area. The resultspresented show, among other things, that the influence ofdegree of ageing is in principle negligible. A possibleexplanation for this behaviour could be that diffusion takesplace in the maltene phase, which is relatively unaffected byageing. The change in recorded rheological parameterscorrelated fairly well with the rates of diffusion observedusing FTIR-ATR, which indicates that chemical diffusion isaccompanied by changes in binder stiffness. Nothing in theresults presented regarding structural stability of mixtures ofold and new binder suggests that binder stability should be alimiting factor in asphalt recycling, on condition that the oldand new binder are compatible. The doctoral thesis is based onthe following papers, which will be referred to by their Romannumerals:I. Karlsson R., Isacsson U.?Material-Related Aspectsof Asphalt Recycling?State-of-the-art?Submittedfor publication in ASCE J of Transportation Eng.II. Karlsson R., Isacsson U.?Application of FTIR-ATRto Characterisation of Bitumen Rejuvenator Diffusion?Accepted for publ. in ASCE J of Materials in Civil Eng.III. Karlsson R., Isacsson U.?Bitumen RejuvenatorDiffusion as Influenced by Ageing?Int?l J of RoadMaterials and Pavement Design. 3(2) 2002IV. Karlsson R., Isacsson U.?Laboratory studies ofdiffusion in bitumen using markers?Submitted forpublication in J of Materials Science.V. Karlsson R., Isacsson U., Ekblad J.?RheologicalCharacterisation of Bitumen Diffusion?Submitted forpublication in J of Rheology.VI. Karlsson R., Isacsson U.?Bitumen StructuralStability Characterisation using Turbidimetric Titration?Submitted for publication in Energy and Fuels.

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