Per Redelius

On the Existence of Wax-Induced Phase Separation in Bitumen

In previous research efforts, it has been shown that at elevated temperatures, the wax content in bitumen does not have a significant impact on the rutting behaviour of asphaltic mixes. However, the presence of wax in bitumen does cause a physical hardening effect at lower temperatures, which encourages the propagation of cracks. Using waxy bitumen, asphalt mixtures tended to exhibit a higher fracture temperature. The study implied that the effect of wax on bitumen quality and asphalt mixture performance depended on many factors, such as precise chemical composition of the bitumen and particularly the nature of the wax. In the current paper, the discussion of the effect of wax on bitumen is continued. In this paper, atomic force microscopy and neutron scattering techniques are utilised to confirm the appearance of wax-induced phase separation and a new hypothesis is developed for its effect on the cracking and healing potential of the bitumen.

The structure of asphaltenes in bitumen

ABSTRACT The definition of asphaltenes and some of its chemical properties like polarity and molecular weight is discussed, based on available knowledge. A critical examination of the currently common claim that asphaltenes is dispersed in bitumen in the shape of micelles is made. It is concluded that it is not likely that any micelles exist in bitumen. An alternative model, a thermodynamic solubility model is suggested. As a support for the solubility model, the Hansen solubility parameter is used to describe the solubility properties of bitumen, asphaltenes and maltenes. In the solubility model bitumen is considered to be a mixture of million of different molecules which is kept in solution by its mutual solubility. A continuum of different polarities and molecular weights are necessary for complete stability. The model predicts that if certain fractions are removed from bitumen the stability may be lost resulting in formation of precipitate and phase separations. The usefulness of the model is illustrated by the ability to relate polarity to the elasticity of the bitumen at normal service temperatures (<70°C).

The Morphology of Bitumen-SBS Blends by UV Microscopy: An Evaluation of Preparation Methods

ABSTRACT The morphology of bitumen-SBS blends is studied using Epi-Fluorescence microscopy. Morphology is defined as the partition of polymer-rich and bitumen-rich phases. Existing sample preparation methods for microscopy on bitumen are compared and the obtained morphologies are shown. In a second part, differences in morphology are related to differences in rheological behavior. The morphological properties strongly depend on the temperature, where a sample is taken, upon the cooling rate and upon isothermal annealing periods. During isothermal storage the morphology can undergo major changes. The so-called bulk morphology, which is obtained from a freeze-fractured surface, is different from the morphology seen on the surface which has been in contact with air or with silicon.

Non-classical Wax in Bitumen

ABSTRACT A new procedure for isolation of the wax fraction in bitumen has been proposed. The procedure consists of collecting the fraction SEC II by Size Exclusion Chromatography as suggested in the SHRP program, followed by precipitation at −20°C. The wax was isolated and washed by filtration. Chemical analysis of the wax has been made using TLC/FID, IR spectroscopy, GC/MS and UV/VIS spectroscopy. The results indicate that the material consists mainly of saturated compounds with very small amounts of n-alkanes. There are also small amounts of material present, which show a strong absorption in UV/VIS. To verify that the isolated wax has the ability to crystallise in bitumen, several mixes with bitumen were made. The mixes were analysed using DSC, which verified that the material crystallise in bitumen and thus is regarded as a true crystallising material. Not to confuse the material isolated by the procedure above with the wax isolated by classical procedures, we propose to call our fraction “crystallizing material”.

Asphaltenes in Bitumen, What They Are and What They Are Not

ABSTRACT Asphaltenes in bitumen and crude oil are generally defined as the fraction which is insoluble in n-heptane. There is also a perceived definition which describes asphaltenes as a very polar, high molecular weight fraction in bitumen. The standard definition and the perceived definition are not identical and thus a lot of confusion has been created. In this paper we conclude that the asphaltenes consist of a very heterogeneous fraction with molecular weights from about 250 g/mol up to 2000 g/mol, with an average of about 750 g/mol. The amount of the hetero atoms nitrogen and oxygen is not enough to make asphaltenes particular polar. A careful examination of the chemistry of asphaltenes reveals that they consist basically of three types of molecules, polycyclic aromatic compounds, n-alkanes with a chain length larger than 40 carbons and metal containing porphyrines.

Fatigue Behaviour of Bituminous Materials: From Binders to Mixes

ABSTRACT Test procedures, aiming at measuring fatigue directly on bituminous binders, are increasingly used. The purpose of this paper is to investigate the relevance of this type of binder fatigue tests and to compare the results with laboratory fatigue properties of the corresponding mixes, using one mix composition for all binders, and similar fatigue tests conditions. Eight binders were selected, derived from two crude sources, including an oxidised and two polymer modified samples. All fatigue tests were performed at equi-stiffness levels. A very good relation was seen for the ε6 value (strain level at which fatigue occurs after one million cycles) in binder and corresponding mix fatigue tests, at least for the non polymer modified binders. The polymer modified samples showed an improved fatigue resistance in binder tests, which was only partially reflected in the asphalt mix tests. In addition, more structured binders, as for example after oxidation, showed better fatigue resistance especially at low strain levels, and under the test conditions used. From this study we can conclude that binder fatigue tests are well related to laboratory mix fatigue behaviour for a given mix composition.

The influence of thermal history on binder rutting indicators

ABSTRACT Binder properties, believed to relate to asphalt rutting, were investigated and compared with each other. Included are: parameters derived from oscillatory tests (e.g. the “zero” shear viscosity and the SHRP rutting parameter), parameters derived from static and repeated creep tests and the traditional R&B softening point. Various binders were tested, including low and high polymer modified bitumen, and bitumen modified with commercial waxes. This study shows that for unmodified bitumen all the investigated binder parameters correlate well with each other and would give similar classifications regarding the rutting susceptibility. For modified binders, the parameters related to low frequency or long loading times, give a different ranking than those related to higher frequencies, as for example the SHRP parameter. The storing and preparation conditions prior to the rheological measurement can have a large influence, especially in the range of long loading times or low frequencies. For elastomer modified binders, the homogenization temperature and the corresponding change in micro-structure can have a large impact. For binders with semi-crystalline modifiers, the storage time and storage temperature before testing can introduce large changes in the polymer network building up. The thermal history effects in rheological tests can be related to variations in crystallinity, as shown by calorimetry, or to variations in morphology, as revealed by fluorescence microscopy. Some of the binders were also investigated in the presence of filler, to see if the thermal effects play a similar role in mastic (binder+filler) as in the neat binder.

Correlation Between Bitumen Polarity and Rheology

ABSTRACT In this study, 26 bitumens covering a large variety in crude origin and processing conditions were evaluated, using rheological tests methods and the recently developed bitumen solubility model (BISOM) titrations. In BISOM, bitumen is characterised by its solubility in three different solvents, relating respectively to Van der Waals, polar and hydrogen bonding interactions. Since both BISOM and rheology produce a large number of data, and since it is not possible to change one parameter at a time, to investigate its influence, a statistical program SIMCA was used. In conclusion, it was found that stiffness versus temperature is, for unmodified bitumen, completely determined by the conventional test methods (penetration, R&B, viscosity) as was already stated by Heukelom. However, the shape of the phase angle with temperature or the elastic behaviour at a given stiffness shows a good relation with the parameters determining the hydrogen bonding potential and the polar interactions. The more hydrogen and polar interactions, the more structured the black curve of a particular bitumen.

Asphalt Production at Reduced Temperatures using Zeolites and the Impact on Asphalt Performance

ABSTRACT The potential benefits of producing and paving asphalt at lower temperatures are beyond discussion. There is already a lot of know-how on various techniques for producing warm mix asphalt, but there is insufficient data available about the impact of these techniques on the final performance characteristics of the asphalt. Nynas and BRRC are working together on a research project, to study the most important and promising warm mix techniques on laboratory and field scale. These techniques are: the use of foamed bitumen, the addition of waxes to the bitumen and the addition of zeolites to the mixture. The present paper focuses on the last technique. The performance of warm asphalt mixtures produced with different types and quantities of zeolites is compared to the performance of a reference hot mix asphalt. Several aspects have been studied: compactability, permanent deformation, water sensitivity and low temperature cracking. Small scale field trials were made to validate the findings of the laboratory research.

Material characteristics of long lasting asphalt pavements

ABSTRACT Based on a catalogue of test roads in Denmark, four long lasting test sections constructed in the early 80s were selected for field sampling and extensive laboratory study. This paper focuses on characterizing the bituminous materials used in the test sections. First, asphalt cores were investigated in a non-destructive way using X-ray tomography and indirect tensile stiffness test. The field samples were further analyzed with respect to binder content, air void content, and aggregate gradation. To characterize recovered binders, both chemical and rheological tests were applied. It was found that the long lasting test sections consisted of thick asphalt layers of low air void contents. The wearing courses contained relatively high binder content except for one with a binder content of slightly below 6%. For all the test sections, no propagated cracks were observed. In achieving a long pavement lifetime, aging of bitumen was indicated as one of the key factors. Field aging of bitumen was strongly dependent on the air voids of asphalt mix. In the test sections of low air voids (< 3% at the time of field sampling), extremely slow bitumen aging was observed. The study also shows that field aged bitumens differ significantly in chemical compositions, and the aging- induced stiffing effect tends to correlate with carbonyl compounds and molecular weight, but not with sulfoxides.