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Towards the enhanced applicability of cold mix asphalt:: An experimental study focusing on surface free energies and the breaking and coalescence of bitumen emulsions
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The environmental, social and economic sustainability of our infrastructure network is clearly of paramount importance to the road-engineering sector as well to society at large. Sustainable road materials and reduced transport of those materials therefore play a significant role. Cold mix asphalt (CMA) emulsion technology could be one of the better options for the road industry to explore more thoroughly. Given its lower start-up and equipment installation costs, lower energy consumption and reduced environmental impact, CMA should offer a reliable alternative to some of the Hot Mix Asphalt (HMA) or Warm Mix Asphalt (WMA) options. As CMA is not a new technology, there are many reasons why this material is not currently being used as extensively as it might be. Though risk adverseness of the market may be partly to blame for this, a number of technical challenges and uncertainties related to material behavior are certainly responsible. This thesis has addressed some of the important technical challenges, aiming to provide more guidance in material selection and design, and prediction of the behavior of emulsion-based CMAs. To do so, this research has focused on aspects of the correct formulation of the bitumen emulsions, how to select the correct combinations of material components, and how to control the breaking and coalescence processes in bitumen emulsions better, resulting in usable and predictable adhesive and cohesive bond strengths. Though most of the laboratory and modeling choices that were made in this thesis are based on theoretical considerations, the main contribution is the test protocol development. The systematic surface free energy measurements of the material components, combined with the test set-up to monitor controllably the breaking and coalescence behavior of bitumen droplets in an emulsified environment, gives a new way to approach the design of CMA. It is recommended that future research is focused on taking the developed protocols as a basis for enhanced mix design and making a direct link to validated long-term mechanical properties on the asphalt mixture scale.

Abstract [sv]

Miljömässig, social och ekonomisk hållbarhet är av största betydelse för vår infrastruktur både inom vägbyggnadsområdet och inom samhället i stort. Där kan hållbara vägbyggnadsmaterial och minskade transporter av vägbyggnadsmaterial ge ett betydande bidrag. Tekniken med kallblandade asfaltemulsionsbeläggningar (CMA) är en av de bättre lösningarna för vägbyggnadsindustrin som skulle kunna användas i större utsträckning än som görs för närvarande. Givet teknikens låga uppstarts- och investeringskostnader, minskad energiförbrukning och minskad miljöpåverkan, kan CMA bli ett attraktivt alternativ till varmblandade (HMA) och halvvarma (WMA) asfaltmassor. Då CMA inte är någon ny teknik, finns många skäl att fundera över varför denna teknik inte praktiseras i så stor omfattning idag. Obenägenheten att ta risker med ny teknik på marknaden delvis kan beskyllas för detta, men också ett flertal osäkerheter kopplade till materialegenskaper hos CMA kan också bidra. Denna avhandling har studerat några viktiga tekniska utmaningar med syfte att ge mer vägledning vid materialval och utformning, samt att förutse materialbeteenden hos emulsionsbaserade CMA. För att nå detta har denna forskning fokuserats på sammansättningen av bitumenemulsioner, hur man väljer rätt kombination av materialkomponenter och hur man får en bättre kontroll på brytförloppet och koalescensen, med målet att kunna förutsäga adhesiv och kohesiv bindningsstyrka. Då de flesta laborativa och modelleringsmässiga valen i denna avhandling är baserade på teoretiska överväganden, är det viktigaste bidraget i denna rapport utvecklingen av testprotokollen. De systematiska mätningarna av fri ytenergi hos materialkomponenterna, kombinerat med testmetoder för att på ett kontrollerat sätt studera bryt- och koalescensbeteendet hos droppar i en emulsionsmiljö, ger en ny möjlighet att optimera sammansättningen av CMA. Det rekommenderas att framtida forskning fokuseras på att ta de föreslagna protokollen som bas för förbättrad proportionering och att göra en direkt koppling till validerade mekaniska långtidseffekter på asfaltbeläggningen.

 

 

Nyckelord

 

Bitumen, Kallblandad Asfalt, Mineraler/Aggregat, Fri Ytenergi, Sorption, Kontaktvinkel, Bitumenemulsioner, Brytning och Koalescensen, Emulgatorer, Adhesionsegenskaper.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology , 2018. , p. 58
Series
TRITA-ABE-DLT ; 1802004
Keywords [en]
Bitumen, Cold Asphalt Mixtures, Minerals/Aggregates, Surface Free Energy, Sorption, Contact Angle, Bitumen Emulsions, Breaking and Coalescence, Emulsifiers, Adhesion Promoters.
Keywords [sv]
Bitumen, kallblandad asfalt, mineraler/aggregat, fri ytenergi, sorption, kontaktvinkel, Bitumenemulsioner, brytning och koalescensen, emulgatorer, adhesionsegenskaper
National Category
Engineering and Technology
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-223445ISBN: 978-91-7729-699-7 (print)OAI: oai:DiVA.org:kth-223445DiVA, id: diva2:1184460
Public defence
2018-03-16, Kollegiesalen, Brinellvägen 8, KTH Royal Institute of Technology, Stockholm, Sweden, 10:00 (English)
Opponent
Supervisors
Note

QC 20180221

Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-03-06Bibliographically approved
List of papers
1. Evaluation of adhesive properties of mineral-bitumen interfaces in cold asphalt mixtures
Open this publication in new window or tab >>Evaluation of adhesive properties of mineral-bitumen interfaces in cold asphalt mixtures
2016 (English)In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 125, p. 1005-1021Article in journal (Refereed) Published
Abstract [en]

The performance of asphalt mixtures is strongly influenced by the physical and chemical properties of the minerals and binders used, at various micro to macro scales. In cold asphalt mixtures a process that particularly strongly influences adherence between the minerals and binders (and thus performance) is the wetting of bitumen on the minerals’ surfaces. Their adhesion is influenced by numerous factors and parameters, such as surface free energies of both binders and aggregates in the presence of moisture or dust on the surface of aggregates, mixing temperatures, surface textures including open porosity, nature of the minerals and their surface chemical composition, as well as additives present in the binder phase. However, the relationships involved are not fully understood. Thus, iowever

n this study the surface free energies of both minerals/aggregates and binders were characterized using two approaches, one based on contact angles and the other on vapor sorption methods. Precise specific surface areas of four aggregates and seven minerals were determined using BET (Brunauer, Emmett and Teller) theory, by measuring the physical adsorption of selected gas vapors on their surfaces, and calculating amounts of adsorbed vapors corresponding to monolayer occupancy on the surfaces. Interfacial bond strengths between bitumen and aggregates were also calculated, based on measured surface free energy components of minerals/aggregates and binders, in both dry and wet conditions. The adhesive bond strength for the binder with each mineral/aggregate combination in wet condition has been improved by using additives. The presented study has highlighted the need for accurate measurements of aggregates’ and minerals’ specific surface areas and (hence) requirements to develop new approaches to resolve problems associated with BET-based methods.

 

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Bitumen, Cold Asphalt Mixtures, Minerals/Aggregates, Surface Free Energy, Sorption, Contact Angle.
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-191530 (URN)10.1016/j.conbuildmat.2016.08.155 (DOI)2-s2.0-84985036619 (Scopus ID)
Note

QC 20160902

Available from: 2016-09-01 Created: 2016-09-01 Last updated: 2018-02-21Bibliographically approved
2. Toward a new experimental method for measuring coalescence in bitumen emulsions: A study of two bitumen droplets
Open this publication in new window or tab >>Toward a new experimental method for measuring coalescence in bitumen emulsions: A study of two bitumen droplets
2016 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 494, p. 228-240Article in journal (Refereed) Published
Abstract [en]

Cold mix asphalt (CMA) emulsion technology could become an attractive alternative for the road industry due to low startup and equipment installation costs, diminished energy consumption and reduced environmental impact. The performance of cold asphalt mixtures produced from emulsions is strongly influenced by a good control of the breaking and coalescence process. The wetting of bitumen on the surface of the aggregates is hereby of major importance for the performance of the asphalt. Premature coalescence of the bitumen emulsions away from the surface, could lead to poor adhesion and decreased mechanical strength of the asphalt. Today, the breaking and coalescence mechanisms of bitumen emulsions are still not fully understood due to their complexities and the lack of fundamental experimental methods and existing models. However, in the past years efforts have been made in defining relationships for understanding the bitumen emulsions. In this paper, a new experimental method is presented to study coalescence of bitumen by using shape relaxation of bitumen droplets in an emulsion environment. The coalescence of spherical droplets of different bitumen have been correlated with neck growth, densification and surface area change during the coalescence process. The test protocol was designed in a controlled climate chamber, to study the coalescence process with varying environmental conditions. The kinetics of the relaxation process was influenced by the temperature as well as other parameters. The research showed that the developed test procedure is repeatable and able to study the coalescence process on a larger scale. However, the relationship between the measured parametric relationships at the larger scale and the bitumen emulsion scale still needs further investigation.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Bitumen emulsions, Breaking, Coalescence, Relaxation, Sintering, Light transmission
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-184520 (URN)10.1016/j.colsurfa.2016.01.045 (DOI)000371394800028 ()2-s2.0-84959517932 (Scopus ID)
External cooperation:
Note

QC 20160407

Available from: 2016-04-07 Created: 2016-04-01 Last updated: 2018-02-21Bibliographically approved
3. Investigating effects of salts on the coalescence process in bitumen emulsions
Open this publication in new window or tab >>Investigating effects of salts on the coalescence process in bitumen emulsions
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

The breaking and coalescence process in bitumen emulsions during their application strongly influences the resulting long-term mechanical performance of the cold mix asphalt. This phase separation process is affected by physico-chemical changes at the bitumen/water interface. This paper describes the effects of addition of different salts on the destabilization of bitumen emulsions. This study is limited mainly to cationic rapid setting (CRS) bitumen emulsions and salts which are very commonly added to these emulsions as a stabilizer. However, a few samples with non-ionic emulsifiers were also prepared and analyzed comparatively to understand the electrostatic force balance with varying concentrations of selected salts. The experimental part includes a bitumen droplet relaxation test, droplet size distribution measurement, microscopy, and evaluation of physico-chemical properties of prepared soap solutions e.g. interfacial tension and density measurements. Some experiments on the effect of selected water-soluble organic solvents on the coalescence process were also carried out. The results showed that coalescence was delayed after the addition of salts, while the water soluble organic solvents proved not to affect the emulsion significantly. 

Keywords
Cold Mix Asphalt, Bitumen Emulsions, Breaking, Coalescence, Relaxation, Salts, Organic Solvents.
National Category
Engineering and Technology
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-223443 (URN)
Note

QC 20180221

Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-02-23Bibliographically approved
4. Modelling coalescence process during breaking of bitumen emulsions
Open this publication in new window or tab >>Modelling coalescence process during breaking of bitumen emulsions
2016 (English)In: / [ed] International Society for Asphalt Pavements (ISAP), 2016, p. 1-12, article id Paper 61Conference paper, Published paper (Refereed)
Abstract [en]

Cold mix bitumen emulsion technology is getting a lot of focus by the road industries since a few decades due to the diminished environmental impacts and reduced energy associated with it. The durability and mechanical performance of cold asphalt mixtures very much depend on the breaking, coalescence and phase separation processes in bitumen emulsions; however, the exact nature of the breaking mechanism of bitumen emulsion is not completely understood today. During coalescence or relaxation process, two bitumen droplets are completely fused into a unique spherical droplet and their kinetic is usually recorded in terms of time, denoted as relaxation time or τrelaxation.  In this work, a two dimensional Phase Field model was used to simulate the coalescence process of two bitumen droplets in water phase. The numerical model is based on Finite Element Method and solves Navier-Stokes system of equations coupled with the Cahn-Hilliard equation. The model predictions are validated by direct comparison with the experimental measurements performed in our previous work. Moreover, the study was extended to the small size (order μm) bitumen droplets which are difficult to produce and handle via experimental methods.  

Keywords
Cold Mix Asphalts; Bitumen Emulsions; Coalescence; Breaking Mechanism; Relaxation; Phase Field; Finite Element Method.
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-223442 (URN)
Conference
Paper 61, ISAP Symposium and 53rd Asphalt Peterson Conference, Jackson Hole, WY. USA. July 18-21, 2016.
Note

QC 20180221

Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-02-23Bibliographically approved
5. Effects of surfactants and adhesion promoters on the bitumen-minerals interfacial bond during breaking of bitumen emulsions
Open this publication in new window or tab >>Effects of surfactants and adhesion promoters on the bitumen-minerals interfacial bond during breaking of bitumen emulsions
(English)In: Article in journal, News item (Refereed) Submitted
Abstract [en]

Cold mix asphalt (CMA) emulsion technology has been the subject of research for many decades due to its proven environmental and economic benefits. However, issues relating to its mechanical performance still need to be investigated in order to understand the breaking mechanisms of bitumen emulsions and the surface chemistry involved. Bitumen emulsions are designed to break in a controlled manner to achieve the required level of performance for producing good quality cold asphalt mixtures. In this work, experiments on the coalescence of two bitumen droplets were carried out on a selected grade of Nynas bitumen. In an emulsion environment, the cohesion between bitumen droplets as well as their adhesion to a mineral surface was investigated. The cohesion and adhesion properties were analyzed by varying selected surfactant types and adhesion promoters in the water phase. The research showed that the presence of emulsifiers (with concentrations above the critical micelle concentration) in the water phase inhibits the adhesion of bitumen droplets to the mineral surface. However, a very small addition (0.02%) of adhesion promoter reverses the situation completely, and adhesion is dominant rather than cohesion. Moreover, the kinetics of the coalescence process is strongly controlled by the water phase temperature.

Keywords
Cold Mix Asphalt; Bitumen Emulsions; Breaking and Coalescence; Cohesion; Adhesion; Surfactants; Minerals.
National Category
Engineering and Technology
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-223444 (URN)
Note

QC 20180221

Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-02-23Bibliographically approved

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