Jan F. Branthaver

RELATIONSHIPS BETWEEN ASPHALTENES, HEITHAUS COMPATIBILITY PARAMETERS, AND ASPHALT VISCOSITY

ABSTRACT Historically, asphalt rheology has been described in terms of a colloidal model, which depicts asphalts as dispersions of asphaltenes in petrolenes (maltenes). The model leads to a classification of asphalts into sol, gel, or intermediate categories. Sol and gel type asphalts exhibit differences in physical and chemical behavior. Sol asphalts also are described as compatible, while gel asphalts are described as non-compatible. The relative viscosity of an asphalt, defined as the quotient of the viscosity of the whole asphalt divided by the viscosity of the n-heptane soluble maltene fraction at a given temperature and rate of shear is one measure of asphalt compatibility. Based on this definition of compatibility, asphalts with low values of relative viscosity are designated as compatible and higher values of relative viscosity are designated as incompatible. Asphalt compatibility is also related to the asphaltene content, where asphalts with low asphaltene content are designated as compatible. It...

Effect of Hydrated Lime on Long-Term Oxidative Aging Characteristics of Asphalt

An experiment involving neat asphalts AAD-1, ABD, and their mixtures with two different grades of hydrated lime was conducted to investigate the effect of lime on the long-term aging characteristics of asphalt binders. Rheological properties of unaged and aged asphalt-lime mixtures were measured with a dynamic shear rheometer at 25°C (77°F) and 60°C (140°F). The addition of hydrated lime to one asphalt (AAD-1) effectively reduced oxidative age hardening. In addition, the phase angle reached the same value as aging time reached after approximately 800 h at 60°C in the pressure-aging vessel for AAD-1 and its mixtures with lime. After 800 h of aging, the phase angle was greater for the limetreated asphalt than for the untreated asphalt, and it continued to decrease at a slower rate. This result indicates that the addition of lime to this asphalt increases the initial stiffness of the binder, but, more importantly, it preserves elasticity during long-term oxidative aging. Thus, for this asphalt, at a level of oxidation typical of pavements, limetreated and untreated asphalts arrived at the same viscosity with time, but the lime-treated asphalt had better viscous flow properties than the untreated asphalt. It could then be predicted that the aged, lime-treated asphalt would be more resistant to fatigue cracking. The other asphalt tested (ABD) did not exhibit substantial effects of lime on the rate of oxidative age hardening. This highly compatible, low-asphaltene asphalt is not typical of most paving asphalts. Because hydrated lime has been shown to reduce oxidative age hardening both in the laboratory and during the first few years in the pavement, adding hydrated lime should extend the useful lifetime of most asphalt pavements.

The structure of abelsonite

Abelsonite, a C31 nickel-porphyrin of the deoxophylloerythroetioporphyrin type, is shown to have methyl groups in the 2, 3, 7, 12, and 18 positions and ethyl groups in the 8 and 17 positions by high-resolution, high-field 1H nuclear magnetic resonance and nuclear Overhauser effect studies. Removal of the nickel by treatment with methanesulfonic acid permitted confirmation of the structure on the free base porphyrin and demonstrated structural integrity under the conditions required for demetallation. The structure is best accounted for geochemically by the hypothesis that abelsonite is derived from a chlorophyll.

EFFECT OF FILM THICKNESS ON THE RHEOLOGICAL PROPERTIES OF ASPHALTS IN CONTACT WITH AGGREGATE SURFACE

The effect of the interaction between aggregate and asphalt on asphalt mix properties has been a subject of many studies. However, studies using compacted mixtures cannot isolate the pure effects of the asphalt-aggregate interactions, while studies using mixtures of asphalt and fines cannot determine the asphalt rheology at the interface. In this study, direct measurement of asphalt rheology at the interface is investigated using the sliding plate geometry with machined aggregate plates. Significant differences in the behavior of asphalts in contact with aggregate plates have been observed, especially at low shear rates. One asphalt shows substantial aggregate surface-induced structuring, while another asphalt shows essentially none. In addition, the film thickness effect on the rheological properties of asphalt binders and asphalt aggregate mixtures was investigated. The results strongly show that thin films of asphalt on an aggregate surface have substantially changed rheological properties that are asphalt composition–dependent, and that asphalts that are graded alike as bulk materials do not have the same rheological properties as thin films, in this service environment.

STUDY OF STERIC HARDENING EFFECT OF THIN ASPHALT FILMS IN PRESENCE OF AGGREGATE SURFACE

The interaction between asphalt and aggregate surfaces before and after low-temperature storage (reversible, irreversible, or both) at various film thicknesses was investigated by means of the sliding plate geometry with standard Pyrex glass plates and machined aggregate plates. The study of storage and setting in thin films of asphalts on aggregate surfaces indicates that asphalts interact differently and unpredictably with aggregate surfaces. The phenomenon of steric hardening in thin films appears to be retarded (compared with the same phenomenon in bulk asphalts) during short storage times but is enhanced in contact with aggregate surfaces after several weeks’ storage.

THE INFLUENCE OF METAL-CONTAINING COMPOUNDS ON ENHANCEMENT AND INHIBITION OF ASPHALT OXIDATION

Addition of lime to paving asphalts is known to inhibit oxidative aging of pavements. The mechanism of the action of lime in retarding oxidation is not known. In this work, an asphalt was mixed with a vanadium chelate that is known to strongly promote oxidation in asphalts. This enhancement of oxidation was largely neutralized when the mixtures were combined with hydrated lime. It is possible that lime acts by suppressing the catalytic activity of naturally occurring vanadium compounds that occur in almost all asphalts, although other mechanisms for the action of lime are also possible. The use of vanadium compounds in asphalt aging tests also is discussed.

PREPARATIVE SIZE-EXCLUSION CHROMATOGRAPHY SEPARATION OF SHRP ASPHALTS: CORRELATION WITH YISCOELASTIC PROPERTIES

ABSTRACT Eight core asphalts and eleven other asphalts selected for study in the Strategic Highway Research Program have been separated into two or more fractions by means of preparative size-exclusion chromatography. The first fraction obtained by this technique is believed to consist of materials that form associations and correspond roughly to asphalt dispersed phases. This phase is polar, aromatic, and of high apparent molecular weight. Subsequent fractions obtained by size exclusion chromatography of the asphalts are of progressively lower molecular weight. When the asphalts were separated into nine fractions, the weights of each fraction were plotted versus elution volume to give distinctive bimodal chromatograms, with one exception. The first eluted size exclusion fractions consist of the major viscosity-building components of the asphalts. When these fractions are removed from asphalts, the weight fractions of the residual materials correlate with tan δ (ratio of viscous to elastic moduli)s of the...

THE EFFECT OF MATTALOPORHYRINS ON ASPHALT OXIDATION. II. THE EFFECT OF VANADYL CHELATES FOUND IN PETROLEUM

ABSTRACT Four selected asphalts were blended with zero to five wt. percent of fractions rich in vamady cheltes prepared from two crude oils. The mixture was -coated in a teflon -support, and the whole was heated in an oven at. 113±2°C for 24 hours. The mixture then was analyzed for increases ketone, acid and anhydride functions. in general, functions rich in vanady ponphyrims tended to promote asphalt oxidation, particularly as measured by increase in kentones. Corelation of vanadyl ponphyrim concentration with asphalt oxidation is observed to the direct only if asphalts are mixed with varying amounts of the same fraction derived from the same crude Possible reasons for this phenomenon are discussed in terms of oxidation susceptibility of aspha1ts, the importance of molecular associations, and the relative catalytic activities of metallaporphyrins and other metal chelates

AN INVESTIGATION OF WAXES ISOLATED FROM HEAVY OILS PRODUCED FROM NORTHWEST ASPHALT RIDGE TAR SANDS

ABSTRACT During the late 1970s, the Laramie Energy Technology Center operated two in-situ combustion projects in the Northwest Asphalt Ridge tar sand deposit of Utah. Some of the heavy oils produced were observed to have high pour points, which resulted in handling problems in cold weather. These heavy oils contain waxes, which were found to be n-alkane homologues ranging past carbon number 60. These alkanes seem to have been derived from what are probably Ozokerite veins, which are found in the tar sand deposit. Samples from these veins and waxes derived from produced heavy oils were studied using 13C NMR, IR, and chemical ionization mass spectrometry.

Surfactants in aged asphalt and impact μ on moisture susceptibility of laboratory-prepared mixes

ABSTRACT Short-term aging (rolling thin-film oven test) of an asphalt binder resulted in the production of surfactants (surface-active compounds), while long-term aging (pressure aging vessel test) of asphalt binders resulted in the production of not only surfactants but also strong acids. The strong acids were identified as being sulfonic acids. It was proposed that the generation of surfactants and/or sulfonic acids in asphalt binder would promote moisture damage in asphalt-aggregate mixes. The surfactants could act as a detergent and emulsify components of the mix, and sulfonic acids could attack the aggregate surface, thus, disrupting the asphalt-aggregate interface. A model compound, p-dodecylbenzenesulfonic acid, which incorporates these two structural features, was used as a modifier in several different mixes. Briquets fabricated from the modified mixes were tested for moisture susceptibility using the freeze-thaw pedestal test. It was observed that those mixes, which were originally not susceptible to moisture damage, were now susceptible. It was also noted that the addition of lime to the aggregates prior to the fabrication of the briquets counteracted the influence of p-dodecylbenzenesulfonic acid.