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Adhesive surface characteristics of bitumen binders investigated by Atomic Force Microscopy
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
SP Technical Research Institute of Sweden, Box 5607, SE-114 86 Stockholm, Sweden . (YKI)
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.ORCID iD: 0000-0003-0889-6078
2013 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 113, 248-256 p.Article in journal (Refereed) Published
Abstract [en]

Bitumen is a complex hydrocarbon whose composition-structure-property relationship is not well-understood. In this paper, microphase-separated topographic morphologies of unaged penetration grade 70/100 bitumen binders have been visualized by means of AFM QNM, and the relationship to local mechanical properties has been demonstrated. AFM QNM is a surface force mapping technique which measures parameters such as topography, adhesion and elastic modulus simultaneously. The resulting data can then be presented as images representing individual or overlaid parameters, e. g. topographic images with an adhesion overlay or topographic images with a modulus overlay. AFM QNM results show that the adhesive forces measured in the region surrounding (peri phase) the periodic topographic features resembling 'bees' (catana phase) and the region in the 'bee' areas are lower than the adhesive force measured in the smooth matrix (para phase). Likewise it was 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).

Place, publisher, year, edition, pages
2013. Vol. 113, 248-256 p.
Keyword [en]
Bitumen, AFM, Adhesion, Young's modulus, Topography
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-107700DOI: 10.1016/j.fuel.2013.05.042ISI: 000323937300029Scopus ID: 2-s2.0-84879473761OAI: oai:DiVA.org:kth-107700DiVA: diva2:577698
Projects
T7729T7736
Note

QC 20130320. Updated from submitted to published.

Available from: 2013-03-20 Created: 2012-12-16 Last updated: 2017-12-06Bibliographically 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.
Series
TRITA-TSC-PHD, 2014:004
National Category
Civil Engineering Materials Engineering
Identifiers
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)
Opponent
Supervisors
Note

QC 20140609

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

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