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 is claimed that the Heithaus parameters also are measures of asphalt compatibility. Therefore there should be a relationship between relative viscosities (π_rel), Heithaus parameters, and n-heptane asphaltene volume fractions ( φn-heptane)- Such a relationship has been derived assuming that the Heithaus p_a parameter is numerically equivalent to α in the Pal-Rhodes equation.     

高粘度改性沥青的性能评价

根据虹桥综合交通枢纽工程钢桥面铺装的技术要求,对国产高粘度改性沥青进行了沥青性能和混合料性能的评价试验,并与某进口高粘度改性沥青进行了对比。试验结果表明：国产高粘度改性沥青与进口高粘度改性沥青的性能相当,两种沥青均符合工程的技术要求,并具有优异的路用性能。此外,测试了不同温度条件下国产高粘度改性沥青的粘度,试验结果表明在高温条件下,该沥青的粘度与普通的改性沥青差异很小,其混合料生产和施工温度可参考普通的改性沥青的相关规定执行。     

THE EFFECT OF ASPHALT COMPOSITION ON THE FORMATION OF ASPHALTENES AND THEIR CONTRIBUTION TO ASPHALT VISCOSITY

ABSTRACT

Interactions among asphalt components have significant effects on the performance of asphalt binder. To understand those interactions, four asphalts, SHRP AAA-I, AAD-I, AAF-I, and AAG-I, were fractionated into three generic fractions according to Corbett's procedure and reblended into asphaltenes/aromatics/saturates ternary mixtures in various ratios. Mixtures were oxidatively aged with atmospheric air at temperatures of 87.7, 93.3, and 98.8°C for 5 to 33 days. The changes in chemical composition and physical properties were monitored using fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical rheometry

The formation of asphaltenes is a major factor in the hardening of asphalt with aging. The data collected in this study indicate that the saturate content in the maltene phase has a profound impact on the contribution that asphaltenes have on the viscosity of aged asphalt. The data also suggest that the aromatics fraction is solely responsible for the formation of asphaltenes as an asphalt oxidizes.     

Oxidation Hardening Kinetics of the Rheological Function G′/(η′/G′) in Asphalts

Abstract

The authors used 9 asphalts oxidized at various temperatures and pressures to determine the hardening kinetics for the DSR function, an easily measured and meaningful surrogate for 15°C ductility that relates well to age-related binder deterioration. For each asphalt, there is a rapid initial period that slows to a constant rate period. This constant rate period can be represented by carbonyl formation (oxidation) rate times a hardening susceptibility (HS). For the DSR function and viscosity, the HS and initial jump were pressure- but not temperature-dependent. The DSR function initial jump was relatively higher than the viscosity initial jump.     

A STUDY ON AGING KINETICS OF ANSHAN PAVING ASPHALT

ABSTRACT

The aging processes of two Anshan paving asphalts conforming to GB/T15180-94 standard have been studied by Rotation Thin Film Oven Test (RTFOT) and the aging kinetic models of two paving asphalts have been determined. The results show that the aging of the prepared paving asphalt is a first order reaction. The viscosity of the asphalt increases gradually with the aging time. The greater the aging index is, the more easily the asphalt is aged. Because the chains break down to form free radicals, oxidation reactions occur. The aging resistance of the asphalt with lower aromaticity and with less aromatic cycle numbers is weak.     

ASPHALT DURABILITY: FROM LABORATORY TEST TO FIELD IMPLEMENTATION

ABSTRACT

Spray and chip seals are the most important form of road surfacings in Australia. The long term hardening of the asphalt binder (its durability) is of critical importance in determining their life. The Australian Road Research Board (ARRB) Durability Test measures the intrinsic resistance of an asphalt cement to oxidative hardening and has been used in specifications for many years. A model which allows calculation of the rate of asphalt hardening in a sprayed seal has already been presented. It is based on data from road trials monitored for up to 15 years.

A second model now permits calculation of the viscosity level at which seal distress occurs in a particular climatic area. By using the combined models it is possible to predict surfacing life. The parameters required for the calculation are the average temperature at the site and the asphalt Durability Test result.

Application of the models to sites; in the U.S. suggests that, if seal lives comparable to those in Australia are to be achieved, it may be necessary to control asphalt durability in the southern part of the U.S. In temperate climate areas only moderately durable asphalts may be necessary. Climatic conditions in the north of the U.S. and in Canada are outside the range of the model but it is clear that binder hardening proceeds at a very slow rate in these regions. Asphalt durability may not be a critical factor in surfacing life in these areas.

The situation for hot mixed a.c. is much more complex than for sprayed seals but the trends; in seal life indicated by the models may provide a guide to a.c. behaviour     

USE OF THE ENVIRONMENTAL SCANNING ELECTRON MICROSCOPE TO INVESTIGATE THREE POLYMER MODIFIED ASPHALTS

ABSTRACT

Polymer modified asphalts present an opportunity to enhance the properties of asphalt concrete for road building where conventional asphalts are not appropriate. In this field, researchers have proposed different kinds of chemical and physical techniques to define the properties of these materials. At the same time, microscopic techniques were being developed to visualize the microstructure of the asphalt. In this paper another microscopic technique using Environmental Scanning Electron Microscopy (ESEM) to investigate the morphological structures of neat polymers and commercial polymer modified asphalts is presented. Samples examined present different kinds of morphology easily observable by ESEM. The two commercial polymer modified asphalts show numerous differences, but after heat treatment they lost their macrostructure.     

SIZE EXCLUSION CHROMATOGRAPHY STUDIES OF AGED SHRP ASPHALTS

Abstract

One of Ihe objectives of the Strategic Highway Research Program is the development of a test procedure that accurately predicts pavement aging. In order to accomplish this goal, the nature and mechanism of oxidative-aging of asphalts must be known.

Eight asphalts were aged in a pressure-oxidation vessel at 60°C (140°F) and 2.07 x 10⁶ Pa (300 psi) for 144 hours (6 days) after a preliminary thin-film oven treatment. The tank asphalts and aged asphalts were separated by preparative size exclusion chromatography into two fractions: one consisting of large molecular size, associated molecules and the other consisting of smaller molecules with less tendency lo associate. The amount of the large molecular size fraction is greater in an aged asphalt compared with its parent tank asphalt. Number-average molecular weights of this large molecular size fraction increase substantially in some aged asphalts but not in others. Viscosities of smaller molecular size fractions (which comprise the bulk of both aged and unaged asphalts) of aged asphalts are not greatly different from viscosities of corresponding fractions of parent tank asphalts. Viscosities of the small molecular size fractions are much lower than viscosities of whole asphalts. Oxygen-containing functional groups were observed in both size exclusion chromatography fractions of all eight aged asphalts.

The above results can be rationalized by invoking a model of asphalt structure in which complex structural units composed of polar and/or aromatic molecules arc dispersed in a less polar solvent phase. The aping process causes buildup of more polar molecules, which increases the relative amounts of asphalt components that engage in associative behavior.     

ANALYSIS OF SHHP ASPHALT NONPOLAR FRACTIONS BY SUPERCRITICAL FLUID CHROMATOGRAPHY

ABSTRACT

Three different fractions derived from each of eight SHRP asphalts were analysed by means of supercritical fluid chromatography. The three fractions were a low molecular weight neutral fraction obtained by ion exchange chromatography, a low molecular weight fraction obtained by size exclusion chromatography, end maltenes obtained by precipitation with hydrocarbon solvents. For a given asphalt, these fractions contain much of the same material and all comprise over one-half of the bulk of the asphalts. The ion exchange chromatography neutral fractions contain minimal amounts of polar materials. Based on the microstructural model of asphalt structure, any one of the three fractions might be considered to represent the solvent phase of an asphalt.

The supercritical fluid chromatograms of the asphalt fractions showed that they comprise materials of widely ranging carbon numbers, from 30 to over 110. Chromatograms of all three fractions of each asphalt are similar, particularly the low molecular weight size exclusion chromatography fractions and the maltenes. Chromatograms of fractions derived from different asphalts can differ greatly. The chromatograms of fractions of sol-type asphalts exhibit peaks corresponding to constituents that are more aromatic and of higher carbon number compared with chromatograms of fractions of gel-type asphalts. Thus supercritical fluid chromatography is a useful tool for the investigation of relatively nonpolar fractions derived from asphalts     

CHARACTERIZATION OF ASPHALTS CEMENTS BY THERMOMICROSCOPY AND DIFFERENTIAL SCANNING CALORIMETRY: CORRELATION TO CLASSIC PHYSICAL PROPERTIES

ABSTRACT

Numerous thcrmoanalyttcal methods can be used to evaluate asphalt cements. Optical thermomicroscopy techniques such as phase contrast microscopy and polarized light microscopy have been used to directly observe the in situ crystallization of aliphatic, waxy fractions, and to monitor any changes in structure that occur with temperature. These visual changes are then correlated with enthalpy changes resulting from precipitation/dissolution as measured by Differential Scanning Calorimetry (DSC) to better understand their thermal behavior. Temperature cycling studies show the phenomenon of crystallization to be completely reversible.

Finally, the Tg and % crystallizable fraction as quantitatively determined by DSC are compared to classic physical properties of the asphalt cement. The Tg compares favorably to the glass transition temperature as measured by a dynamic mechanical analyzer at low frequencies, but correlations with the Fraass Brittle Temperature are lower than expected. Asphalts with large amounts of crystallizable material as measured by DSC show significant aberrations from a rheological mastercurve typical of homogeneous viscoelastic fluids, and these results become more pronounced with time. These same asphalts also exhibit changing rheological behavior as the thermal treatment of the sample is varied prior to testing. suggesting that crystallization requires time and fluidity for molecular agglomeration to occur.

Hence, asphalt can and docs exist as a beterogcncous, biphasic liquid at ambient temperatures when sufficient crystallizable fractions are present. DSC offers a rapid, accurate technique to quantify this phenomenon and predict its effect on asphalt performance     

FRACTIONATION OF ASPHALT MATERIALS BY USING SUPERCRITICAL CYCLOHEXANE AND PENTANE

ABSTRACT

Fractionation of asphalt materials by using supercritical cyclohexane and pentane has been successfully conducted. Each of three asphalts was fractionated into ten fractions. These asphalts and their fractions were then characterized by a variety of analyses including Corbett chromatographic separation, infrared analysis, refractive index- and intrinsic viscosity-size exclusion chromatography (gel permeation chromatography), and elemental analysis by atomic absorption. The fractions were then reblended to produce materials of typical asphalt consistency. These blends were then subjected to oxidative aging in a pressure oxidation vessel and were found, in some cases, to have improved aging characteristics in the sense that they did not harden in response to a given carbonyl formation (oxidation) as much as normal asphalt materials. Hence, the supercritical fractionation technique is considered to have great potential for producing improved asphalt materials.     

ELIMINATION CHEMISTRY IN ASPHALT

ABSTRACT

The objective of this work was to determine the feasibility of modifying asphalt AAK-2 and AAM-2 by elimination reactions. The dehydrohalogenation reaction and the dealkylation reaction were investigated. Brominated asphalt AAK-2 and AAM-2 can be produced via free-radical chain reaction. The dehydrobrominated asphalt AAM-2 showed an increase in large molecular size (LMS) materials, no elastic recovery and an increased ESR free radical signal intensity. However, the dehydrobromination modified asphalt AAK-2 showed an increase in elastic recovery compared to the original asphalt. In this case, no increase in the ratio of the ESR signal intensity of vanadyl porphyrins to free radicals was observed. The dealkylation reaction modified asphalt AAK-2 showed an increased elastic recovery and a weight average molecular weight reduction, due to its high sulfur and nitrogen content. The ratio of the ESR signal intensity of vanadyl porphyrine to free radicals was decreased. A plot of log [ESR signal intensity ratio] versus aging index yielded a straight line for eight core asphalts studied. Therefore, an increase in the free radical concentration in asphalt may correlate with the loss of elastic recovery, increased W S materials and increased viscosity. The feasibility of modifing asphalt MK-2 and AAH-2 vas successfully demonst Gated: The results obtained here not oil; provide methods for chemically modifying asphalt but also provided information on - oxidation - reactions of asphalt nitrogen content. The ratio of the ESR signal intensity of vanadyl porphyrine to free radicals was decreased. A plot of log [ESR signal intensity ratio] versus aging index yielded a straight line for eight core asphalts studied. Therefore, an increase in the free radical concentration in asphalt may correlate with the loss of elastic recovery, increased W S.     

Study on Aging Capability of Paving Asphalt

Abstract:

The changes of softening point, penetration, and ductility of two asphalts after aging were studied. Two methods are simultaneously used to study the aging kinetics of two asphalts and some kinetic parameters are given in this paper. The results show that the softening points increase while penetration and ductility values decrease after aging. It was concluded that the aging capability of AH-70 asphalt is better than AH-90 asphalt. The aging kinetic models of two asphalts based on softening points are compared with a pentane asphaltene aging kinetic model and the results are consistent. A new and easy method for studying the aging of asphalt was developed.     

Influence of Chemical Composition on the Physical Characteristics of Paving Asphalts

Abstract

The simplest general compositional model considers asphalt to be made up of asphaltenes, heavy oils, and resins. In the present study the extent of similarity between the properties and composition of various types of asphalt obtained from different sources has been carefully explored. It shows how ductility, penetration, and softening point are related to the chemical nature of paving asphalts in the range 41–58 softening points. Asphalt properties are found to be a direct function of its chemical constituents. The relationship between softening point and asphaltene content was found to be linear while asphalts of the same softening point are easily distinguished by the content of the resins. Evaluation of the two asphalt indices—the asphaltene index (I _A ) and the Gaestel index (I _C ), reveals that they both vary linearly with the composition of asphaltenes and resins thus confirming their suitability in the characterization of asphalts. Comparison of the two indices shows that IC is more suitable in estimating the colloidal stability of different groups of asphalts. The observed correlations can be found useful in the areas of asphalt blending and rejuvenating through the appropriate selection of asphalt components.     

STUDY OF SATURATED COMPONENTS IN ASPHALT

ABSTRACT

The saturated fractions separated from blown and straight run asphalts of the same penetration grade have been investigated by using GC, MS and ¹³ The saturated components in asphalt represent complex mixture of polyalkyl structures in which straight chain paraffins prevail. The content of saturates in asphalt and their molecular composition were found to be affected by the chemical nature of crude oil as well as by the method of its processing into asphalt. Saturated fractions from blown asphalt are richer in long chain paraffins than those from straight run asphalts. The structural examination of saturated components separated from the products of asphalt pyrolysis has confirmed die presence of long straight-chain units in the asphalt-forming micelles. The structural differences between the saturated fractions obtained from asphalts of different origin (Uralian and Brent-blend) suggest, that the distribution of straigh-chain hydrocarbons in asphalts is dependent on the aliphatic network already existing in the raw material.     

Studies on Nigerian Crudes IV. Improvement of Asphaltic Properties of Residual Asphalts

Abstract

Residual asphalts obtained from 25 samples of Nigerian light, medium, and heavy crude oils were chemically treated by air-oxidation and sulfurization to improve their characteristic properties. The asphalt yield for light crudes varied from 27.7–33.7 wt% and 33.4–67.5 wt% for medium crudes. The chemical treatment brought about changes in chemical composition, increase in molecular mass and modification of consistency resulting in highly improved asphaltic properties. There were manifold increases in viscosity and softening points, which came as a result of the higher asphaltene content of the treated materials. The asphalts obtained meet quality specifications for typical commercial grade products thus confirming the suitability of Nigerian crude oils for the production of residual asphalts.     

ION EXCHANGE CHROMATOGRAPHY SEPARATION OF SHRP ASPHALTS

ABSTRACT

Eight asphalts selected for intensive study in the Strategic Highway Research Program have been separated into neutral, basic, and acidic fractions by means of ion exchange chromatography. Each asphalt exhibits a characteristic fractionation pattern into neutral, acidic, and basic components. The separations into chemical types were verified by elemental analysis and infrared methods. Separations were reasonably repeatable, and recoveries were acceptable. Large enough amounts of asphalts could be separated so that properties of interest of the fractions could be studied.

In all cases, neutral fractions comprised at leaBt one-half of the asphalts. These neutral fractions are the least aromatic and contain the lowest percentages of heteroatoms and metals compared with the polar fractions. They also are much lower in molecular weight. The viscosities of the neutral fractions are at least two orders of magnitude lower than parent asphalt viscosities measured at the same temperature and rate of shear. The neutral fractions have properties predicted by a model of asphalt structure, which postulates that polar, aromatic materials are dispersed in a less aromatic, nonpolar solvent phase The polar fractions are friable solids or tacky semisolids. Them polar fractions also have properties predicted for dispersed phases in the above mentioned model of asphalt structure. They are more aromatic, contain larger percentages of heteroatoms, and are of higher molecular weight than neutral fractions. The polar fraction designated as the strong acid fraction is the most abundant an d most aromatic of the ion exchange chromatography polar fractions. and it also contains the largest concentration of polar functional groups     

ABSORPTION OF ASPHALT INTO POROUS AGGREGATES: TEST OF A SIMPLE PHYSICOCHEMICAL MODEL

ABSTRACT

Absorption is the process in which asphalt flows into a porous aggregate, under the driving force of capillary pressure. Asphalt absorption is of interest because it represents an economic loss of effective binder, and because it may change the properties of the resulting asphalt film and lead to premature pavement distress. Incorrect air voids estimation may also result from failure to properly account for asphalt absorption in pavement design. The objective of this research was to determine the temporal dependence of absorption upon asphalt and aggregate properties and to test a rational model for this dependence.

Absorption data were obtained for several model liquids and asphalts with synthetic alumina aggregates and a natural limestone aggregate. The data were used to test a simple absorption model incorporating the effects of asphalt and aggregate properties into a single dimensionless time variable.

While quantitative agreement was not obtained in all aspects of the model, certain predictions of the model were verified. The general shape of the absorption data followed the model prediction for synthetic alumina spheres. The effect of viscosity and surface tension was correlated fairly well by the surface tension/virosity factor in the dimensionless time variable

The use of the dimensionless time variable was able to reduce the time span for absorption from ca. four order of magnitude to only ca. one order of magnitude; although, there remained a significant variation in some of the absorption data, probably caused by differences in the contact angles for the various Liquids.

The absorption behavior with a natural Iowa limestone did not follow the shape of the theoretical curve predicted by the model. This deviation is thought to be c a d by the presence of air in the pores coupled with the large and polydisperse pore size of this aggregate     

POLARITIES OF SHRP ASPHALTS CALCULATED FROM ION EXCHANGE CHROMATOGRAPHY SEPARATION DATA

Abstract

During the Strategic Highway Research Program, four asphalts were separated into polar and non-polar fractions by means of three different ion exchange chromatography procedures. For each asphalt, the non-polar neutral fractions comprised over 50 mass percent of the total asphalt. These neutral materials are much less viscous than corresponding whole asphalts. Molecular weights of the neutral fractions correlate roughly with viscosities, whereas there is no correlation between these properties for whole asphalts.

The various polar fractions were subdivided into acidic, basic, and amphoteric fractions of differing polarities. Based on dipole moments of typical components, polarity factors were assigned to each of these fractions. Multiplication of mass percentages of each fraction by their polarity factors yields polarity indices. Total polarities of asphalts or mixtures of ion exchange fractions are obtained by summing polarity indices of the unique distribution of components. Polarities of asphalts and mixtures of ion exchange fractions and viscosities of neutral fractions can be used to predict viscosities of whole asphalts and mixtures.

The method allows for prediction of effects on Theological properties of asphalts by materials whose polarities can be estimated. The success of the method supports one model of asphalt structure.     

Effect of Chemical Nature on the Susceptibility of Asphalt to Aging

Abstract

The knowledge of the factors affecting the susceptibility of asphalt to aging can be of help when selecting the asphalt binders for the construction of durable pavements. Investigated were the aging-induced changes in the chemical composition and colloidal nature of asphalts differing in origin and technology. It was shown that the course of the changes in the generic composition of asphalt upon aging under laboratory conditions depends on the chemical type of the feedstock from which the asphalt has been derived. During aging of the asphalts from the paraffin–naphthenic crudes, the resins undergo partial decomposition, which results in the increase of the cyclic fraction content. Although the increase of the asphaltene content in air-blown asphalts after the Thin Film Oven Test was found to be lower than that in the corresponding straight-run asphalts, the much higher value of the instability index and smaller size distribution of asphaltenes in the air-blown asphalts permit us to expect that their utilization as binders in pavement construction will lead to the reduction of pavement durability. It follows from the results of this study that not only the generic composition but also the structure of the fractions affect the resistance of asphalt to aging.