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Fundamental investigation to improve the quality of cold mix asphalt
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Cold mix asphalt (CMA) emulsion technology could become an attractive option for the road industry as it offers lower startup and equipment installation costs, energy consumption and environmental impact than traditional alternatives. The adhesion between bitumen and aggregates is influenced by diverse parameters, such as changes in surface free energies of the binder and aggregates or the presence of moisture or dust on the surface of aggregates, mixing temperatures, surface textures (including open porosity), nature of the minerals present and their surface chemical composition, as well as additives in the binder phase. The performance of cold asphalt mixtures is strongly influenced by the wetting of bitumen on surfaces of the aggregates, which is governed by breaking and coalescence processes in bitumen emulsions. Better understanding of these processes is required. Thus, in the work this thesis is based upon, the surface free energies of both minerals/aggregates and binders were characterized using two approaches, based on contact angles and vapor sorption methods. The precise specific surface areas of four kinds of aggregates and seven minerals were determined using an approach based on BET (Brunauer, Emmett and Teller) theory, by measuring the physical adsorption of selected gas vapors on their surfaces and calculating the amount of adsorbed vapors corresponding to monolayer occupancy on the surfaces. Interfacial bond strengths between bitumen and aggregates were calculated based on measured surface free energy components of minerals/aggregates and binders, in both dry and wet conditions.

In addition, a new experimental method has been developed to study bitumen coalescence by monitoring the shape relaxation of bitumen droplets in an emulsion environment. Using this method, the coalescence of spherical droplets of different bitumen grades has been correlated with neck growth, densification and changes in surface area during the coalescence process. The test protocol was designed to study the coalescence process in varied environmental conditions provided by a climate-controlled chamber. Presented results show that temperature and other variables influence kinetics of the relaxation process. They also show that the developed test procedure is repeatable and suitable for studying larger-scale coalescence processes. However, possible differences in measured parametric relationships between the bitumen emulsion scale and larger scales require further investigation.

There are several different research directions that can be explored for the continuation of the research presented in this thesis. For instance, the rationale of the developed method for analyzing coalescence processes in bitumen emulsions rests on the assumption that the results are applicable to large-scale processes, which requires validation. A linear relationship between the scales is not essential, but it is important to be able to determine the scaling function. Even more importantly, qualitative effects of the investigated parameters require further confirmation. To overcome the laboratory limitations and assist in the determination of appropriate scaling functions further research could focus on the development of a three-dimensional multiphase model to study coalescence processes in more detail, including effects of surfactants, pH and other additives such as mineral fillers and salts. Additionally, better understanding of the breaking process and water-push out could help significantly to optimize CMA mix design. Different methods, both numerical and experimental could be explored for this.

Abstract [sv]

Cold mix asphalt (CMA) eller kall asfaltbetong med hjälp av emulsionsteknik kan vara ett attraktivt alternativ för vägbyggnadsindustrin då det möjliggör lägre uppstart- och investeringskostnader, lägre energiförbrukning och mindre miljöpåverkan än traditionella alternativ. Adhesionen mellan bindemedel och stenpartiklarna påverkas av ett flertal parametrar, så som förändring i fri ytenergi hos både bindemedel och partiklar i närvaro av fukt eller damm på stenytorna, blandningstemperatur, yttextur (inklusive ytporositet), mineralegenskaper och ytornas kemiska sammansättning lika väl som tillsatsmedel i bindemedlen. Beteendet hos kall asfaltbetong är starkt påverkad av vätningsegenskaperna hos bindemedlet när det kommer i kontakt med stenmaterialet och detta i sin tur är beroende på bitumenemulsionens brytegenskaper och förmåga att blandas. Bättre förståelse av dessa processer är av största vikt. I detta arbete är avhandlingen baserad på fri ytenergi hos både mineraler/aggregat och bindemedel, baserat på kontaktvinkel och på ångabsorptionsmetoder. Den exakta specifika ytan hos fyra typer av aggregat och sju mineraler undersöktes med en metod baserad på BET (Brunauer, Emmett och Teller):s teorier genom att mäta den fysiska adsorptionen av utvalda gaser på ytorna och beräkna mängden adsorberad ånga som korresponderade mot ytlagret. Styrkan hos kontaktytornas bindning mellan bindemedlet och stenaggregaten beräknades baserat på mätningar av den fria ytenergin hos bägge ingående komponenterna, dels i torrhet dels i våta omgivningar.

Som tillägg har en ny experimentell metod utvecklats för att studera bitumens blandbarhet genom att studera bitumendroppars relaxation i en emulsionsmiljö. Genom att använda denna metod har korelationen mellan sväriska droppar av bitumen undersökts mot förändringen i ytans area under blandningsprocessen. Testprotokollet utformades för att studera blandningsprocessen i varierande miljöer i en klimatkammare. Presenterade resultat visar att temperatur och andra variabler påverkar de kinetiska förhållandena vid relaxationsprocessen. De visar även att den utvecklade testmetoden är repeterbar och passar för studier av storskaliga blandningsprocesser. Det bör dock påpekas att vidare studier krävs för att påvisa skillnaderna mellan bitumenemulsionsskalan och större skalor.

Framtida forskning kommer att koncentreras på utveckling av tredimensionella multifas­modeller för att studera blandningsförlopp på en mer detaljerad nivå, inkluderande effekter på ytaktiva ämnen, pH-värden och andra additativ så som mineralfiller och salt. Som tillägg kommer nyttan av nya karaktäriseringsmetoder att utvärderas, så som lågvikelspridning av neutroner eller kombinationer av röntgen, neutronradiologi och datortomografi, för att studera brytmekanismer hos bitumenemulsioner vid kontakt med mineraler och aggregat.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 59 p.
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 142
Keyword [en]
Bitumen, Cold Asphalt Mixtures, Minerals/Aggregates, Surface Free Energy, Sorption, Contact Angle, Bitumen Emulsions, Breaking and Coalescence.
Keyword [sv]
Bitumen, kallblandad asfaltmassa, mineraler/aggregat, fri ytenergi, sorption, kontaktvinkel, bitumenemulsion, brytning och blandning.
National Category
Infrastructure Engineering
Research subject
Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-191527OAI: oai:DiVA.org:kth-191527DiVA: diva2:957207
Presentation
2016-09-26, B2, Brinellvägen 23, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20160901

Available from: 2016-09-01 Created: 2016-09-01 Last updated: 2016-09-01Bibliographically approved
List of papers
1. Surface energy measurements and wettability investigation of different minerals and bitumen for cold asphalts
Open this publication in new window or tab >>Surface energy measurements and wettability investigation of different minerals and bitumen for cold asphalts
2014 (English)In: Asphalt Pavements - Proceedings of the International Conference on Asphalt Pavements, ISAP 2014, CRC Press, 2014, Vol. 1, 61-70 p.Conference paper (Refereed)
Abstract [en]

For environmental reasons, low installation cost and initial investment; low energy infrastructure materials are becoming of high interest. A potential option to replace current hot mix asphalts is emulsifications, where bitumen binder is dispersed in a water phase aided by emulsifier and shear forces, and mixed at ambient temperature with unheated stones. Long term performance must, however, be guaranteed, otherwise the application benefits will be significantly diminished. In this paper, the main issues of cold mix (emulsion based) asphalt, like wetting in the presence of moisture and dust, and coalescence issues are discussed. Since both bitumen droplets and mineral surfaces were upscaled, pure mineral surfaces were investigated as stone material consists of different minerals. As a measure of the interfacial bond strength, surface free energies of different mineral aggregates and bitumen have been investigated in this paper as a stepping stone for further analyses of emulsions. From the analyses it was found that bitumen has only dispersive forces whereas most of the minerals surfaces have polar nature. According to Fowke's additive nature of the forces, bitumen and water are roughly equally strongly adsorbed to plagioclase and calcite, whereas water will displace bitumen from quartz, gypsum, potassium feldspar and mica surface.

Place, publisher, year, edition, pages
CRC Press, 2014
Keyword
Low energy infrastructure materials, cold mix asphalts, bitumen emulsions, wettability, minerals Surface energy
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-158305 (URN)000347408100007 ()2-s2.0-84904122214 (ScopusID)978-1-138-02693-3 (ISBN)978-1-315-73675-4 (ISBN)
Conference
12th International Conference on Asphalt Pavements, ISAP 2014, Raleigh, NC, United States, 1 June 2014 through 5 June 2014
Note

QC 20150107

Available from: 2015-01-07 Created: 2015-01-07 Last updated: 2016-09-01Bibliographically approved
2. 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
(English)In: Construction and Building Materials, ISSN ISSN: 0950-0618Article in journal (Refereed) Accepted
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.

 

Keyword
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)
External cooperation:
Note

QC 20160902

Available from: 2016-09-01 Created: 2016-09-01 Last updated: 2016-09-12
3. Toward understanding breaking and coalescence of bitumen emulsions for cold asphalts
Open this publication in new window or tab >>Toward understanding breaking and coalescence of bitumen emulsions for cold asphalts
2016 (English)Conference paper (Other academic)
Abstract [en]

Cold mix asphalt (CMA) emulsion based technology is a potential option to replace traditional hot mix asphalt due to environmental benefits and less energy consumption of producing it. However, there are some issues concerned with CMA, for instance, pre-mature coalescence of bitumen emulsions while mixing with minerals or aggregates, which might need more attention to improve the performance of CMA. Actually, the adhesion between the binder and the aggregate surface is largely dependent on the breaking process of bitumen emulsions and the water push-out from the mixtures. This breaking process helps to predict the materials behavior as well as the long term mechanical performance of the mixtures; however, the exact nature of the breaking mechanism of bitumen emulsion is not completely understood until today. The objective of this research is to develop understanding of the structural changes during the phase separation and coagulation stages of the bitumen emulsion. Wettability of bitumen was analyzed by changing the substrate climate conditions. Moreover, this study was extended with the addition of emulsifier and other additives to the binder itself as well as to the water phase. Similar kinds of experiments were setup for exploring the coalescence of bitumen drops in water and emulsifier with other additives.

Keyword
Cold Mix Asphalts, Bitumen Emulsions, Coalescence, Breaking Mechanism, Wettability, Surface Free Energy.
National Category
Infrastructure Engineering
Research subject
Transport Science
Identifiers
urn:nbn:se:kth:diva-191534 (URN)
External cooperation:
Conference
6th Euroasphalt & Eurobitume Congress, Czech Republic, June 1-3, 2016
Note

QC 20160902

Available from: 2016-09-01 Created: 2016-09-01 Last updated: 2016-09-02Bibliographically approved
4. 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, 228-240 p.Article 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
Keyword
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 (ScopusID)
External cooperation:
Note

QC 20160407

Available from: 2016-04-07 Created: 2016-04-01 Last updated: 2016-09-12Bibliographically approved

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