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.     

An Accelerated Method for Determining Asphalt Oxidation Kinetics Parameters for Use in Pavement Oxidation and Performance Modeling

A new and innovative strategy has been developed for using the pressure aging vessel (PAV) at 90°C and 100°C and elevated pressure (2.1 MPa) for predicting asphalt oxidative embrittlement and its consequent loss of durability over years of pavement service. At elevated pressure and temperature, the method requires significantly less time, days not months, to determine atmospheric oxidation kinetics parameters than tests at 1 atm. Nevertheless, it allows fundamentals-based durability predictions specific to each material and pavement climate. One atmosphere kinetics parameters predicted from PAV data using a new correlation, together with a pavement oxidation and performance model, form the new performance prediction strategy.     

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.     

EVALUATION OF AN EASTERN SHALE OIL RESIDUE AS AN ASPHALT ADDITIVE

ABSTRACT

An evaluation of eastern shale oil (ESO) residue as an asphalt additive to reduce oxidative age-hardening and moisture susceptibility was conducted. The ESO residue, having a viscosity of 23.9 Pa"s at 60°C (140°F) was blended with three different petroleum-derived asphalts, AAD-1, AAK-1, and AAM-1, that are known to be very susceptible to oxidative aging. Rheological and infrared analyses of the unaged and aged asphalts and the blends were then conducted to evaluate oxidative age-hardening. In addition, the petroleum-derived asphalts and the blends were coated onto three different aggregates, Lithonia granite (RA) a low-absorption limestone (RD) and a silicious Gulf Coast gravel (RL) and compacted into briquets. Successive freeze-thaw cycling was then conducted to evaluate the moisture susceptibility of the prepared briquets. The abbreviations used above for the asphalts and the aggregates are part of the Strategic Highway Research Program nomenclature.

The rheological analyses of the unaged petroleum-derived asphalts and their respective blends indicate that the samples satisfy the rutting requirement. However, the aging indexes for the RTFO-aged and RTFO/PAV-aged samples indicate that the blends are stiffer than the petroleum-derived asphalts. This means that when in service the blends will be more prone to pavement embrittlement and fatigue cracking than the petroleum-derived asphalts. Infrared analyses were also conducted on the three petroleum-derived asphalts and the blends before and after RTFO/PAV aging.     

STUDY OF SERIAL REACTION KINETICS AND CHANGES OF GROUP COMPOSITIONS OF PETROLEUM ASPHALTS IN CONTINUOUS HEAT AND AIR AGING

ABSTRACT

The serial reaction kinetics and the changes of group compositions of Shengli petroleum asphalt(SPA) and Huansanlian petroleum asphalt(HPA) were studied during continuous heat and air aging(CHAA) at 120 ～ 180°C. The test results show that at given temperature the contents of saturate constituents of two asphalts change very little, aromatic constituents decrease clearly and asphaltenes increase gradually during CHAA. At lower temperatures(120 ～ 140 °C) the contents of resins increase slowly and no toluene insolubles form obviously, but at higher temperature(180°C) the resins increase at first and then decrease and the toluene insolubles increase much quickly with the CHAA time. The higher the CHAA temperature, the more evidently the change of asphalt group compositions would change. The apparent aging rate constants and the apparent aging activation     

A Study on Antiaging Performances of Two Paving Asphalts

Abstract

In this article, the processes of Anshan oxidizing paving asphalts have been studied and the kinetic models for two paving asphalts were put forward. Based on the change of service performances, viscidity, and Gastel index (Ic), the aging resistance of the two asphalts have been compared. Meanwhile, the aging mechanism also has been investigated. The results show that the presented dynamics models can be used to describe the aging velocity for the two asphalts perfectly. According to dx/dt(AH-90) > dx/dt(AH-70), it can prove that the aging resistance of AH-70 is better than that of AH-90. After aging, the change of both penetration and softening point of AH-70 are lower than that of the corresponding parameters of AH-90, and the aging index of AH-70 is also lower than that of AH-90, which proves that the aging resistance of AH-70 is better than that of AH-90. During aging, every composition tends to be transformed into the heavier one. As a result, the asphltene content increases, the original colloidal structure of asphalt is destroyed to deteriorate paving performances of the asphalt.     

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.     

CHEMICAL TRANSFORMATION OF RESIDUAL ASPHALTS FROM NIGERIAN CRUDES

ABSTRACT

An atmospheric - vacuum distillation of both light and medium Nigeria crudes was carried out to obtain residual asphalts. Subsequent air-oxidation of the asphalts at 200°C and 240°C for a period of one hour resulted in the improvement of their properties The oxidation reaction led to a 2 - fold increases in asphaltene content and the viscosity of the residual asphalts. The softening points of the upgraded asphalts show that they meet acceptable standard for road paving purposes.     

A Study on Aging Kinetics of Asphalt Based on Softening Point

Abstract

Asphalt aging is a nonreversible first order reaction, and the extent of asphalt aging is usually expressed by the increase of its softening point. In this article, the first order aging kinetic model of asphalt has been put forward based on softening points of asphalt at different aging time, and the kinetic parameters have been obtained. The results showed that the aging of asphalt could be described with softening point and belonged to first order kinetics, which offered a available and convenient method for studying the asphalt aging behavior. The aging resistance of two paving asphalts were also compared by this model.     

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.     

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.     

THE EFFECT OF METALLOPORPHYRINS ON ASPHALT OXIDATION. I. EFFECT OF SYNTHETIC METAL CHELATES

ABSTRACT

Two different asphalts were coated on a Fluoropak support and were oxidized at 130 ± 2^°C for 24 hours using a number of metal chelales as additives. After oxidation the recovered asphalts were analyzed by infrared spectrometry to determine enhancements of keto, acid, and anhydride functions. Vanadyl etioporphyrin I was found to be an effective promoter in the oxidation of both asphalts. Vanadyl porphyrins having bulky ring substituents are not as effective as vanadyl etioporphyrin I in promoting asphalt oxidations.     

A DUAL,SEQUENTIAL MECHANISM FOR THE OXIDATION OF PETROLEUM ASPHALTS

ABSTRACT

Examination of kinetic data for asphalt oxidative age hardening and the chemistry of the oxidation reactions has led to the proposal of a sequential, dual mechanism for asphalt oxidation. The dual mechanism rationalizes conflicts between results of earlier mechanistic investigations and provides a fundamental explanation for the hyperbolic-like, property-versus-time plots characteristic of asphalt oxidative aging. The oxidation kinetics are in harmony with and provide further confirmation of the microstructural model of asphalt. It is proposed that the rapid oxidation rate at the onset of asphalt oxidation results from reaction of oxygen with a limited amount of highly reactive hydrocarbon components. Final oxidation products of this initial reaction are sulfoxides and most likely aromatized rings. During this initial reaction, a much slower oxidation of benzytic carbons is initiated with both ketones and sulfoxides being formed. The ratio of ketones to sulfoxides formed and the rate of oxidative age hardening were found highly dependent on temperature and oxygen pressure (concentration). Significant differences were found in the oxidation and age hardening kinetics of pressure vessel aged asphalts and asphalts aged at atmospheric pressure. Atmospheric pressure oxidation was significantly more sensitive to variations in temperature and asphalt composition than was pressure vessel oxidation at 100°C.     

Investigation on the thermal decomposition performance and long-term storage performance of HNIW-based PBXs through accelerated aging tests

ABSTRACT

2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW)-based polymer-bonded explosives (PBXs) were prepared through an aqueous suspension method using cellulose acetate butyrate (CAB) or fluorine rubber F₂₃₁₁ as a binder. Then the variation rules of mass, surface micro-topography, mechanical properties, thermal decomposition performance, detonation velocity and mechanical sensitivity of the samples before and after accelerated aging tests for different durations were measured. Then the variables of the samples that before and after accelerated aging tests for different durations, will be measured, these variables including the variation rules of mass, surface micro-topography, mechanical properties, thermal decomposition performance, detonation velocity, and mechanical sensitivity. The PBX columns showed an acceptable mass loss of less than 1%, after accelerated aging tests. The surface of the PBX samples became more and more uneven as the aging duration prolonged, which was in a good agreement with the order of mass loss. Moreover, the tensile strength, the thermal stability, the detonation velocity and the mechanical sensitivity of the samples were not significantly affected by the aging process, suggesting that the PBXs remained valid after an accelerated aging test at 60°C for 60 days. A further estimation using the modified Arrhenius equation revealed that the storage life at ambient temperature (20°C) of the HNIW-based PBXs was over 10 years, which satisfies the application demands for explosives.     

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 after long-term storage (5 months) at room temperature of 25°C. Infrared spectroscopic analytical results on asphalt binders show that sulfoxide and ketone form during storage. It is interesting to note that the molecular structuring effect in asphalt-aggregate mixtures could be partially eliminated by heating to a temperature above 100°C for a short period of time (20 seconds). The results also show that the aggregate surface-induced structuring as well as the asphalt composition contribute to the long-term storage hardening of asphalt-aggregate mixtures at low temperature.     

Changes in rheological properties during asphalt aging

The deterioration of asphalt binders rheological behaviors in different aging stages were investigated by using self-developed indoor aging equipment SAT (simple aging test), and the corresponding relationship between indoor simulated aging and field asphalt aging was established. It was found that SAT equipment can better simulate the aging process of asphalt on site, with asphalt film thickness of 2?mm, short-term aging temperature at 150?°C, long-term aging temperature at 95?°C.     

紫外线作用下道路沥青老化行为研究

为了研究紫外线老化下沥青性能变化,选取同种产地、不同标号的两种基质沥青以及两种常规改性沥青,分析基质沥青在不同紫外线老化后组分变化,研究四种沥青在不同时长紫外绒老化后的三大指标、DSR和BBR试验。结果表明,选用沥青老化后C/H值来评价同种来源基质沥青紫外老化性能是可行的,并可以通过使用DSR、BBR补充评价基质沥青和改性沥青紫外线老化后的高低温流变性能。     

A Study on the Aging Kinetics of PPA Modified Asphalt

Abstract

Asphalt binders have been chemically modified with polyphosphoric acid (PPA) since the early 1970s. A large number of research papers have shown that the addition of PPA to asphalt improved the high-temperature stability and rheological properties of asphalt. In this article, research on the aging kinetics of PPA-modified asphalt was carried out based on determining the softening point of asphalts at different aging time and temperatures. The results showed that the aging reaction of PPA-modified asphalt followed the first-order reaction; the aging reaction rate of PPA-modified asphalt was lower than that of original asphalt; the activation energy of PPA-modified asphalt was higher than that of original asphalt; and the anti-aging performance of PPA-modified asphalt was better than that of original asphalt.     

COMPARISON OF OXIDATION OF SHRP ASPHALTS BY TWO DIFFERENT METHODS

An objective of the Strategic Highway Research Program is the development of a test procedure that accurately predicts changes in asphalt pavement properties with aging. Many of the methods now in use do not give reliable results. It is desirable to develop a method that takes into account maximum temperatures to which asphalts are subjected in mix plants (about l60°C or 320°F) and during service (60° C or 140°F), but is not impractically long. Therefore, test conditions must involve increased temperature, pressure, or the addition of a chemical accelerant but yield artificially aged materials that have certain properties similar to those of aged pavement binders.|In this study, rheological and chemical properties of asphalts subjected to thin-film oven followed by pressure vessel oxidation under two sets of conditions were compared with properties of asphalts aged in the thin-film accelerated-aging test at two temperatures. Oxidations of asphalts for 144 hours (6 days) at 60°C (I40°F) and 2.07 × 10⁶ Pa pressure following a standard thin-film oven treatment yielded products having characteristic aging indices and enhanced sulfoxide and carbonyl absorbances in their infrared spectra. Oxidation of asphalts under thin-film accelerated-aging lest conditions at 85°C (185°F) for 144 hours provides aged asphalts with rheological properties similar to those obtained from the 60°C (140°F) pressure oxidations. When the pressure oxidation was run at 80°C (176°F) for 144 hours. materials were obtained that were more extensively aged. The aging indices of these materials were somewhat similar to asphalts oxidized for 72 hours at 113°C (235.4°F) under thin-film accelerated-aging test conditions. The aging lendencies of the eight asphalts tested were ranked by the two latter methods in approxmiately the same order.|The thin-film accelerated-aging test procedures are readily performed in a standard oven. but utilize smaller samples (resulting in less material for subsequent analysis) than the pressure oxidations. It is not certain that the mechanism or kinetics of the asphalt oxidations in the higher temperature oven procedures are identical to the mechanisms of oxidation of asphalts in pressure aging. The procedures used in this study, although not themselves definitive test conditions for asphalt-binder aging. should aid in the selection of conditions for an improved aging lest.     

Characterization of hard-grade asphalt using entropy analysis

By adopting different technologies and raw materials, several kinds of hard-grade asphalts were prepared, and the correlation between performances and chemical compositions for these hard-grade asphalts was investigated based on grey relation entropy analysis. Results indicated that nine types of hard-grade asphalts were in accordance with GB/T 15180-2010 standard for 30# asphalt, although they have obvious differences in the performances. The main factors influencing high temperature performances were the presence of aromatics and resins and molecular weight distribution, while the main factors influencing temperature susceptibility were the presence of saturates and asphaltenes and the unstability of colloids. While there has been slight difference in E_r(X_i) for ductility (10°C and 15°C), the remarkable factors influencing the crack resistance at low temperature (stiffness and m value) were the presence of aromatics and resins and molecular weight distribution, in accordance with high temperature performances.