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Surface wrinkling: The phenomenon causing bees in bitumen
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
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2013 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 20, 6970-6976 p.Article in journal (Refereed) Published
Abstract [en]

The so called "bee phenomenon" in bitumen has been investigated by means of AFM quantitative nanomechanical property mapping. Bees are a phenomenon that can be observed by topography measurements using AFM. The characteristic "bee" appearance comes from regions with alternating higher and lower bands in the surface topography of bitumen, which are surrounded by a flat area. The proposed mechanism for bee formation is phase separation and differential contraction during cooling from melt temperatures leading to wrinkling due to differences in the elastic modulus of the material phases. Using a laminate wrinkling model, the thickness of the bee laminate was calculated from the wavelengths and Young's moduli of the bee laminate and the matrix. It was found to vary between 70 and 140 nm for the five bitumen samples that contained significant amounts of wax.

Place, publisher, year, edition, pages
2013. Vol. 48, no 20, 6970-6976 p.
Keyword [en]
Atomic-Force Microscopy, Crude Oils, Sacrificial Bonds, Wax, Morphology, Particles, Talc, Afm
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-126046DOI: 10.1007/s10853-013-7505-4ISI: 000322277700013ScopusID: 2-s2.0-84881122549OAI: diva2:641913

QC 20130820

Available from: 2013-08-20 Created: 2013-08-19 Last updated: 2014-06-10Bibliographically approved
In thesis
1. A Fundamental Adhesion Model for Asphalt
Open this publication in new window or tab >>A Fundamental Adhesion Model for Asphalt
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the mechanisms for the deterioration of asphalt is debonding. This is often referred to as stripping. Most losses of adhesion at the bitumen-aggregate interface are attributed to the action of water leading to a reduction in properties such as tensile strength, tensile stiffness and wear resistance. If we move to more accurate models for predicting bitumen-aggregate adhesion based on material properties, then we can be much more effective in building roads that are stable and resist hardening, crack-building, and stripping more effectively.

The main aim of this doctoral thesis was to propose a hypothesis for what makes bitumen binders stay adhered to aggregates (or filler particles such as Portland cement) and to provide a fundamental understanding for the development of a new test method for bitumen-aggregate adhesion.

The Hamaker constant was used to estimate van der Waals interactions. Hamaker’s constant is composed of two parts. The first part describes the Keesom and Debye contribution, which represents the attraction energy at zero-frequency, and the second part the London dispersive (electronic) contribution, which represents the attraction energy in the optical/UV spectrum. Calculations of Hamaker’s constant require accurate dielectric data, i.e. the dielectric constant and the refractive index of the interacting materials and the intervening medium.

Paper I: Hamaker’s constant was introduced to describe and calculate the van der Waals interaction and to determine its relationship to resistance to stripping.

Paper II: The dispersive component of minerals was calculated from their refractive indices using data from mineral data sheets.

Paper III: The dispersive component of un-aged bitumen and aggregates was calculated from their refractive indices, determined by ellipsometery measurements.

Paper IV: The surface force mapping technique, AFM QNM, was used to measure parameters such as topography, adhesion and elastic modulus simultaneously on un-aged 70/100 penetration grade bitumen binders. The result was presented as images representing individual and overlaid parameters, e.g. topographic images with an adhesion overlay and topographic images with a modulus overlay. The adhesion forces measured in the region surrounding (peri phase) the ‘bees’ (catana phase) and the region in the ‘bee’ areas are lower than the adhesion force measured in the smooth matrix (para phase). Likewise it can be observed that Young’s moduli in the region surrounding (peri phase) the ‘bees’ (catana phase) and in the ‘bees’ are higher than Young’s modulus of the smooth matrix (para phase).

Paper V: The mechanism for bee formation was investigated via AFM.

Paper VI: The bitumen components that are expected to migrate to the air interface and to the surface of laboratory glass slides (or to the surface of aggregates), were investigated based on the relative dielectric spectroscopic response of the material components, as determined by their dielectric constants and refractive indices.

The total polarizability can be determined from the dielectric constant. The non-polar London dispersive (electronic) polarizability can be determined from refractive index measurements. In materials with higher permittivity at zero frequency the Keesom and Debye attraction energies will be responsible for a significant part of the polarization. Bitumen as a whole has a low degree of total polarizability. Bitumen contains a small fraction of n-heptane insoluble molecules that have a somewhat higher total polarizability and therefore may contribute to Debye and Keesom interactions. Bitumen as a whole is highly London dispersive (electronic) polarizable and the asphaltene (or n-heptane insoluble) fraction is even higher London dispersive (electronic) polarizable. The degree of non-polar London dispersion polarizability increases with increasing molecular size and with increasing aromaticity.

Paper VII: Adhesion properties of un-aged 70/100 penetration grade bitumen binders were probed by means of permittivity analysis.

The initial adhesion of non-aged bitumen binders to pure quartz aggregates is primarily London dispersive due to low total polarizability of the components.

The higher surface coverage with the addition of the Portland cement to the surface of the aggregates can be explained by the addition of components with higher London dispersive polarizability and higher total polarizability of CaO, MgO and ironoxides. Portland cement is a material contributing to Debye and Keesom interactions. Portland cement could also have chemical influence on its bonding to aggregates.

A strong correlation was identified between the average tangent of the dielectric loss angle in the frequency region of 0.01 to 1 Hz and surface coverage (a common method to indicate suitability of bitumen for use in roads). Surface coverage is higher for bitumen binders having a larger average loss tangent.

It is suggested that the average tangent of the dielectric loss angle in the frequency range of 0.01 to 1 Hz, could be used as an indicator for predicting polarizability and thereby, adhesion potential of bitumen binders.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. x, 44 p.
TRITA-TSC-PHD, 2014:004
National Category
Civil Engineering Materials Engineering
urn:nbn:se:kth:diva-146226 (URN)978-91-87353-42-0 (ISBN)
Public defence
2014-06-13, Sal D2, Lindstedtsvägen 5, KTH, Stockholm, 10:00 (English)

QC 20140609

Available from: 2014-06-10 Created: 2014-06-10 Last updated: 2014-06-10Bibliographically approved

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