Raymond E. Robertson

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.

Modeling of Oxidative Aging Behavior of Asphalts from Short-Term, High-Temperature Data as a Step Toward Prediction of Pavement Aging

The oxidative aging data collected during the Strategic Highway Research Program have been analyzed in terms of kinetics of viscosity change with time and temperature. Changes in viscosity have been used as the measure of the progress of aging. The objective is to model viscosity increases accurately enough to be able to predict aging (in terms of viscosity changes) at pavement temperatures from short-term test data acquired at high temperature. This involved constituting a mathematical model, based on oxidative reactions, and a nonlinear regression of the data to test predictability of the proposed model. Clearly, there is a point beyond which viscosity change becomes independent of time, but no data were collected to that extent. Separately, it has been shown that oxidation of aliphatic sulfide to sulfoxide and oxidation of benzylic carbon to carbonyl are the principal chemical reactions that contribute to an increase in viscosity. The data fit the proposed equation sufficiently well to allow calculatio...

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.

A STUDY OF RHEOLOGICAL PROPERTIES OF LIME TREATED PAVING ASPHALTS AGED AT 60°C IN A PRESSURE AGING VESSEL

Abstract The oxidation and age-hardening propensities of eight widely varying petroleum asphalts used for paving were studied with and without hydrated lime, and with inert particulate matter in place of lime. The results show that oxidation of sulfides to sulfoxides and benzyl carbon to ketone is affected very little by the presence of lime. However, the addition of lime does inhibit age-hardening in asphalt whereas the inert particulate matter in the same amount and particle size has little effect other than the filler effect exhibited by the lime and the inert particulate. The principal inhibition of age-hardening of asphalt by hydrated time occurs at high pavement temperatures (> 60°C). At low and moderate temperatures (<50°C), age-hardening is very slow and typically not a major problem in pavement. It is speculated elsewhere in detailed aging studies that the high temperature age-hardening of paving asphalts results from formation of multimolecular, three dimensional matrices in asphalt formed among...

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...

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 EVALUATION OF SHALE OIL-MODIFIED ASPHALT WITH POLYMER-MODIFIED ASPHALTS

Since the discovery, patenting by Western Research Institute, and licensing to The New Paraho Corporation of a concept for the use of an asphalt modifier that can be produced from western shale oil, nine test strips have been constructed in five states in the United States. Performance evaluations were conducted on three shale oil-modified asphalt (SOMAT) test pavements that were laid in Utah and Wyoming. In all cases the performance of the test pavements was compared with pavement sections that were constructed using polymer-modified asphalts. The results of the evaluation of the pavement performance at the three project sites in general show that rutting, fatigue cracking, and thermal cracking properties of the SOMAT (test) pavements are comparable to the AC-20R and PBA-6a (control) pavements. However, with respect to moisture susceptibility and in-service aging, the SOMAT pavements are less prone to moisture damage and are aging at a slower rate than the control pavements. A life cycle cost analysis was conducted on the SOMAT and AC-20R pavements laid south of Moab, Utah, on U.S. Highway 191. The projected terminal service life for the two pavements, assuming that no remedial actions are taken, is 28 years for the SOMAT test strip and 7 years for the AC-20R control section. The cost of these remedial actions was estimated on the basis of the realization that remedial actions would be conducted and assuming a 30-year service life. The total estimated cost for the SOMAT pavement was

Effect of Aggregates on Isothermal (Steric) Hardening of Asphalts

171,218/lane-mile, and for the AC-20R pavement it was