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Storage Stability and Phase Separation Behaviour of Polymer-Modified Bitumen: Characterization and Modelling
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. (Highway Engineering Research Group)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polymer-modified bitumen (PMB) is a high-performance material for road construction and maintenance. But its storage stability and phase separation behaviour are still not sufficiently understood and need to be studied toward a more successful and sustainable application of PMB. In this thesis, the equilibrium thermodynamics and phase separation dynamics of PMB are investigated with the aim at a fundamental understanding on PMB storage stability and phase separation behaviour. The development of polymer modifiers for paving bitumen is reviewed. The phase separation process in unstable PMBs is captured by fluorescence microscopy at the storage temperature (180 °C). A coupled phase-field model of diffusion and flow is developed to simulate and predict the PMB storage stability and phase separation behaviour. The temperature dependency of PMB phase separation behaviour is modelled by introducing temperature-dependent model parameters between 140 °C and 180 °C. This model is implemented in a finite element software package and calibrated with the experimental observations of real PMBs. The results indicate that storage stability and phase separation behaviour of PMB are strongly dependent on the specific combination of the base bitumen and polymer. An unstable PMB starts to separate into two phases by diffusion, because of the poor polymer-bitumen compatibility. Once the density difference between the two phases becomes sufficiently significant, gravity starts to drive the flow of the two phases and accelerates the separation in the vertical direction. The proposed model, based on the Cahn-Hilliard equation, Flory-Huggins theory and Navier-Stokes equations, is capable of capturing the stability differences among the investigated PMBs and their distinct microstructures at different temperatures. The various material parameters of the PMBs determine the differences in the phase separation behaviour in terms of stability and temperature dependency. The developed model is able to simulate and explain the resulting differences due to the material parameters. The outcome of this study may thus assist in future efforts of ensuring storage stability and sustainable application of PMB.

Abstract [sv]

Polymermodifierade bitumen (PMB) är ett högpresterande material för väganläggning och underhåll. Men PMB:s lagringsstabilitet och fassepareringsegenskaper är inte tillräckligt förstådda än och behöver studeras för en mer framgångsrik och hållbar användning av PMB. I denna avhandling studeras termodynamisk jämvikt och fasseparation av PMB med målsättning att uppnå en grundläggande förståelse av PMB:s lagringsstabilitet och fassepareringsegenskaper. Utvecklingen av polymermodifierade bitumen sammanfattas. Fasseparationsprocessen av instabil PMB:s studeras med hjälp av fluorescens mikroskopi vid lagringstemperatur (180 °C). En kopplad fas-fälts modell som beskriver diffusion och flöde har utvecklats för att simulera och förutsäga PMB:s lagringsstabilitet och fassepareringsegenskaper. Temperaturberoendet hos PMB:s fasseparation har beskrivits genom att införa temperaturberoende modellparametrar mellan 140 °C och 180 °C. Denna modell är införd i ett finit element program och kalibrerad med experimentella observationer på verkliga PMB. Resultaten indikerar att lagringsstabiliteten och fasseparationen hos PMB är starkt beroende av den specifika kombinationen av basbitumen och polymer. En instabil PMB börjar separera i två faser genom diffusion, beroende på dålig bitumen-polymer kompatibilitet. När skillnaden i densitet mellan de två faserna blir tillräckligt stor kommer gravitationen att driva flödet av de två faserna och accelerera separationen i vertikalled. Den föreslagna modellen, baserad på Cahn-Hilliards ekvation, Flory-Huggins teori och Navier-Stokes ekvation, kan beskriva stabilitetsskillnaderna mellan de undersökta PMB:erna och deras distinkta mikrostruktur vid olika temperaturer. De olika materialparametrarna hos PMB bestämmer skillnaden i fassepareringsegenskaper i termer av stabilitet och temperaturberoende. Den utvecklade modellen kan simulera och förklara de resulterande skillnaderna på grund av materialparametrarna. Resultatet av denna studie kan bidra till att säkerställa lagringsstabilitet och hållbara applikationer för PMB.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 71 p.
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 143
Keyword [en]
Polymer-modified bitumen; Storage stability; Phase separation; Fluorescence microscopy; Phase-field modelling
Keyword [sv]
Polymermodifierad bitumen, Lagringsstabilitet, Fasseparation, Fluorescensmikroskopi, Fas-fälts modellering
National Category
Infrastructure Engineering
Research subject
Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-195089ISBN: 978-91-7729-187-9OAI: oai:DiVA.org:kth-195089DiVA: diva2:1044013
Public defence
2016-11-22, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20161102

Available from: 2016-11-02 Created: 2016-11-01 Last updated: 2016-11-02Bibliographically approved
List of papers
1. Polymer modification of bitumen: Advances and challenges
Open this publication in new window or tab >>Polymer modification of bitumen: Advances and challenges
2014 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 54, no 1, 18-38 p.Article, review/survey (Refereed) Published
Abstract [en]

Advances and challenges in the field of bitumen polymer modification for road construction during the last 40 years are reviewed in this paper. The history of bitumen polymer modification is described chronologically. Some popular plastomers and thermoplastic elastomers in bitumen modification are discussed regarding their advantages and disadvantages, including polyethylene (PE), polypropylene (PP), ethylene-vinyl acetate (EVA), ethylene-butyl acrylate (EBA), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS) and styrene-ethylene/butylene-styrene (SEBS). Although these polymers all improve bitumen properties to some extent, there are still some drawbacks limiting the future development of bitumen polymer modification, such as high cost, low ageing resistance and poor storage stability of polymer modified bitumen (PMB). Researchers attempted various ways to remove these drawbacks. Some technical developments for removing drawbacks are reviewed in this paper, including saturation, sulfur vulcanization, adding antioxidants, using hydrophobic clay minerals, functionalization and application of reactive polymers. The future development of polymers for bitumen modification is analyzed as well. Since it is currently challenging to perfectly achieve all expected PMB properties at the same time, some compromised recommendations are given in this paper, among which greatly enhancing the properties with an acceptably high cost, significantly reducing the cost with relatively poor properties and their combinations. Functionalization is emphasized as a promising way to enhance the properties of currently used polymers and develop new-type polymer modifiers with much greater success in the future. It is also recommended that future research on bitumen polymer modification focuses more on function development towards enhancing: adhesion with aggregates, long-term performance and recyclability.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Advance, Challenge, Future development, Polymer modified bitumen
National Category
Infrastructure Engineering Polymer Technologies
Research subject
Transport Science
Identifiers
urn:nbn:se:kth:diva-144175 (URN)10.1016/j.eurpolymj.2014.02.005 (DOI)000336111000003 ()2-s2.0-84898809979 (ScopusID)
Note

QC 20140612

Available from: 2014-04-11 Created: 2014-04-10 Last updated: 2016-11-01Bibliographically approved
2. Towards the development of a viscoelastic model for phase separation in polymer-modified bitumen
Open this publication in new window or tab >>Towards the development of a viscoelastic model for phase separation in polymer-modified bitumen
2015 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no S1, 39-49 p.Article in journal (Refereed) Published
Abstract [en]

The development of a viscoelastic model for phase separation in polymer-modified bitumen (PMB) is proposed in this paper. PMB is considered as a pseudo-binary blend. Equilibrium thermodynamics and phase separation dynamics of PMB are discussed. The effects of dynamic asymmetry on phase separation in PMB are analysed with related theories and some image data. Based on the discussion in this paper, it is concluded that the effects of dynamic asymmetry between bitumen and polymer should be taken into consideration when studying phase separation in PMB. By analysing related literature and image data, it is found that some features of viscoelastic phase separation are shown during the phase separation process in some PMBs. It is possible to develop a viscoelastic model for PMB to describe its phase separation behaviour. The stress-diffusion coupling would play a key role in the model by introducing composition-dependant mobility, shear and bulk stress.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2015
Keyword
polymer modified bitumen, storage stability, viscoelastic phase separation, model
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-163539 (URN)10.1080/14680629.2015.1030834 (DOI)000355122400004 ()2-s2.0-84929953979 (ScopusID)
Note

QC 20150616

Available from: 2015-04-07 Created: 2015-04-07 Last updated: 2016-11-01Bibliographically approved
3. Experimental investigation on storage stability and phase separation behaviour of polymer-modified bitumen
Open this publication in new window or tab >>Experimental investigation on storage stability and phase separation behaviour of polymer-modified bitumen
2016 (English)In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268XArticle in journal (Refereed) Published
Abstract [en]

Storage stability and phase separation behaviour of four styrene-butadiene-styrene (SBS) polymer-modified bitumen (PMB) binders are investigated by conventional binder tests and fluorescence microscopy in this paper. Since no separation happened in the stable PMBs, research focus was placed on capturing and analysing the phase separation process in the unstable PMBs. A phase inversion phenomenon was observed in one unstable PMB during the phase separation, showing the possible viscoelastic effects. Furthermore, it is indicated that criteria only based on compositional parameters can give misleading predictions of PMB storage stability. New criteria still need to be defined. The potential approaches to PMB phase behaviour prediction are reviewed and exploratively discussed in the context of the four investigated PMBs. This leads to a further discussion on the possibility of having a thermodynamic approach to PMB phase behaviour prediction by looking into the free energy of PMB. The Flory–Huggins theory provides a way to do this, upon the consideration of PMB as a pseudo-binary blend and some made assumptions. Free energy curves have the strength of giving more information like the equilibrium phase composition. In addition, some more aspects should be also considered for PMB phase behaviour prediction towards an applicable criterion.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
Keyword
Polymer-modified bitumen, Storage stability, Phase separation, Fluorescence microscopy, Flory-Huggins theory
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-189976 (URN)10.1080/10298436.2016.1211870 (DOI)2-s2.0-84979085761 (ScopusID)
Note

QC 20160727

Available from: 2016-07-26 Created: 2016-07-26 Last updated: 2016-11-30Bibliographically approved
4. Modelling and numerical simulation of phase separation in polymer modified bitumen by phase-field method
Open this publication in new window or tab >>Modelling and numerical simulation of phase separation in polymer modified bitumen by phase-field method
2016 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 107, 322-332 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a phase-field model with viscoelastic effects is developed for polymer modified bitumen (PMB) with the aim to describe and predict the PMB storage stability and phase separation behaviour. The viscoelastic effects due to dynamic asymmetry between bitumen and polymer are represented in the model by introducing a composition-dependent mobility coefficient. A double-well potential for PMB system is proposed on the basis of the Flory-Huggins free energy of mixing, with some simplifying assumptions made to take into account the complex chemical composition of bitumen. The model has been implemented in a finite element software package for pseudo-binary PMBs and calibrated with experimental observations of three different PMBs. Parametric studies have been conducted. Simulation results indicate that all the investigated model parameters, including the mobility and gradient energy coefficients, interaction and dilution parameters, have specific effects on the phase separation process of an unstable PMB. In addition to the unstable cases, the model can also describe and predict stable PMBs. Moreover, the phase inversion phenomenon with increasing polymer content in PMBs is also well reproduced by the model. This model can be the foundation of an applicable numerical tool for prediction of PMB storage stability and phase separation behaviour.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Polymer modified bitumen; Storage stability; Phase separation; Phase-field method
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-188830 (URN)10.1016/j.matdes.2016.06.041 (DOI)000381532800040 ()2-s2.0-84974808182 (ScopusID)
Note

QC 20160620

Available from: 2016-06-20 Created: 2016-06-20 Last updated: 2016-11-29Bibliographically approved
5. Numerical investigation on phase separation in polymer modified bitumen: Effect of thermal condition
Open this publication in new window or tab >>Numerical investigation on phase separation in polymer modified bitumen: Effect of thermal condition
(English)Manuscript (preprint) (Other academic)
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-195087 (URN)
Note

QC 20161103

Available from: 2016-11-01 Created: 2016-11-01 Last updated: 2016-11-03Bibliographically approved
6. Numerically Predicting Storage Stability of Polymer-Modified Bitumen: A Coupled Model of Gravity-Driven Flow and Diffusion
Open this publication in new window or tab >>Numerically Predicting Storage Stability of Polymer-Modified Bitumen: A Coupled Model of Gravity-Driven Flow and Diffusion
(English)Manuscript (preprint) (Other academic)
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-195088 (URN)
Note

QC 20161103

Available from: 2016-11-01 Created: 2016-11-01 Last updated: 2016-11-03Bibliographically approved

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