Shin-Che Huang

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.

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.

INTERACTION OF ASPHALT FILMS WITH AGGREGATE SURFACES IN THE PRESENCE OF WATER

ABSTRACT Experiments were conducted to investigate the effects of water on mixtures of neat asphalts with two aggregates. In these experiments, samples of mixtures were contacted with warm water for varying lengths of time. When the samples were removed from water, they were dried and then were contacted with n-heptane. This relatively inert solvent dissolves maltenes, precipitates asphaltenes, and should not disturb polar organic molecules of asphalts adsorbed on aggregate surfaces during water soaking. The polar organics then were recovered using a polar solvent and were weighed and studied by infrared spectrometry. The polar organics recovered were adsorbed from neat asphalts and not solutions of asphalts as in other studies. Measurements of the pH of waters in contact with the mixtures indicate that water rapidly penetrates to asphalt-aggregate interfaces in most of the systems studied. In some systems, amounts of polar organics recovered did not change with soak time. In others, amounts of polar organics increased as a result of water soaking, particularly a combination of a waxy asphalt with granite. The infrared results showed that some carbonyl compounds and 2-quinolones are readily displaced from aggregate surfaces by water, as was found in the solvent studies. Sulfoxide groups do not appear to be as labile. Each asphalt-aggregate combination appears to exhibit a characteristic response to water, as is observed in pavements.

Comparative Field Performance of Asphalts from Multiple Crude Oil Sources

A comparative pavement performance site was built in 2001 in central Arizona with four unmodified PG 76-16 asphalts. The four asphalts from different crude oil sources and blends were used to build sections of pavement about three-quarters of a mile long. All other variables (e.g., aggregate source and gradation, geometric and structural design, traffic, climate, and compaction) were held as constant as possible. In a typical project, a construction contractor could have purchased any of the four asphalts because all met the project specifications. Before construction of this site, a search was conducted for existing projects for which the asphalt source was varied and location documentation and original construction materials were available. No such projects were found. The mission was to acquire real-world, long-term pavement performance data for asphalts from different crude oil sources so that the validity of existing and new long-term performance predictive test methods could be examined. The focus was on performance variations related to asphalt crude oil source and thus asphalt compositional features. Several chemical and rheological tests were performed on the asphalts to gain information to relate to field performance. The four asphalt sources showed remarkable differences in performance. Similar comparative pavement performance sites were located in Wyoming, Nevada, Arizona, Kansas, Minnesota, and the Yellowstone National Park east entrance. All sites are monitored annually.

Asphalt mastic characterization by means of chromatography

ABSTRACT Concentrated solutions of asphalts in cyclohexane were separated into non-polar and polar organic fractions by percolation through beds of pulverized aggregates (<200 mesh) mixed with a filter aid. The polar organic fractions were desorbed from the aggregate using a polar solvent. After drying, the polar organic fractions were weighed. Infrared spectra showed that polar functional groups are concentrated in polar organic fractions. Weights of polar organic fractions from eight asphalts separated on seven aggregates varied by a factor of seven. For a given aggregate, asphalts with the highest asphaltene contents yielded the most polar organic fractions, and vice-versa. Two aggregates consistently adsorb substantial quantities of polar organic fractions from the asphalts, and two other aggregates consistently adsorb relatively small amounts of polar organic materials. This rudimentary method should be capable of refinement and speedup. It might be of use in evaluating interactions of asphalts and mineral fines in mastics. In asphalt-aggregate combinations that exhibit comparatively little interaction (as evidenced by adsorption of small amounts of polar organic materials) in mastics, it is unlikely that interactions will be stronger with larger sizes of aggregates. In other cases, too much adsorption of polar organic materials in mastics might adversely affect pavement properties.

A STUDY OF LOW TEMPERATURE HARDENING ON THIN FILM ASPHALT BINDER IN CONTACT WITH AGGREGATE SURFACE

ABSTRACT The interaction between asphalt and aggregate surfaces before and after low temperature storage (reversible and/or irreversible) at various film thickness was investigated by means of the sliding plate geometry with standard Pyrex glass plates and machined aggregate plates. Significant differences in 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 shows essentially none. Moreover, the study of the film thickness effect on the rheological properties of asphalt binders and asphalt aggregate mixtures show that thin films of asphalts on an aggregate surfaces have substantially changed rheological properties from bulk asphalt properties and further, physical properties in thin films are not easily predicted from bulk properties. In addition, the study of storage and setting in thin films of asphalts on aggregate surfaces indicates that oxidative aging occurred afte...