查看更多>>摘要：Traditionally, asphalt concrete requirements are based on recipe specifications for bituminous mixtures; these specifications do not consider changes in the mechanical properties of materials over time. A considerable hardening of bitumen occurs with age, a characteristic that must be considered in the evaluation of bituminous materials. In asphalt concrete evaluation work, such as pavement design or end-product contracts, the age of asphalt materials may have a considerable impact on the outcome. This investigation was undertaken to aid the development of a performance specification that is based on the structural functional properties of asphalt concrete. Properties of asphalt concrete cores from various road sections were evaluated with respect to changes in stiffness and creep over several years, with an emphasis on hardening during the early life of the pavement. Relationships between mechanical properties of bituminous mixtures and age have been established. The results make it possible to take into account the effect of aging during pavement evaluation and during characterization of mixes with respect to aging properties. It was shown that stiffness modulus and creep deformation of bituminous layers can change significantly during the early life of the pavement and that this change should be considered in performance specifications and pavement analysis.
查看更多>>摘要：In this work, the effect that filler has on the aging of bitumen was analyzed but with the filler being incorporated by volume, not by weight. The Universal de Caracterizacion de Ligantes method was used as the process of accelerated aging, and a new direct tensile test was used to determine the toughness of the aged mixture and, thus, to assess the effect the filler has. All tests performed for this paper have shown the protective effect of the fillers used. The new direct tensile test developed by the Road Research Laboratory of the Technical University of Catalonia allows observation of how an increase in filler produces an increase in the breaking load and a decrease in the maximum deformation: the hydra ted lime tends to stiffen the mixture less and make it less brittle than does calcium carbonate. To minimize the effect of aging on bitumen, the filler content proposed must be 20% or 30% less than the content recommended in conditions where there is no aging, so that when the mixture ages, the mastic is able to build up the maximum energy possible.
查看更多>>摘要：The chemical composition of an asphalt binder significantly affects oxidative aging and interactions with both aggregate and binder modifiers. In turn, it may cause premature asphalt pavement failures through fatigue cracking, moisture damage, or other failure mechanisms. Analytical chemical procedures, such as ion exchange Chromatography, are time-consuming and cost prohibitive as routine tests. Inverse gas-liquid Chromatography (IGLC) is a relatively faster and simpler technique that provides the chemical composition and polarity characteristics of asphalt samples. In IGLC, asphalt is used as the liquid substrate on an inert support in a GLC column and is characterized by measuring the retention behavior of selected test compounds that possess different functional groups. The interaction behaviors between seven test compounds and 19 unaged and GLC column-aged asphalt samples were determined and compared with functional group concentrations presented in the asphalts and in a nonaqueous potentiometric titration study. It was found that the retention behaviors of the test compounds are strongly related to the types and concentrations of functional groups in the asphalt. For unaged asphalts, the retention behavior of strongly basic test compounds is highly correlated with the concentration of acidic functional groups in asphalts. The retention behavior of phenol with oxidatively aged asphalts is highly correlated with the concentration of sulfoxide, one of the major products of asphalt oxidation.
Suresh RaghavendraClaudia E. ZapataM. Waseem MirzaWilliam N. Houston...
p.24-32页
查看更多>>摘要：It is well documented that environmental effects play a significant role in characterizing material properties, which in turn affect pavement performance. Studies under the Strategic Highway Research Program (SHRP) were carried out on the age-hardening characteristics of asphalt binders and mixes. As a result, laboratory procedures to simulate the field hardening of asphalt binders and mixes, AASHTO Provisional Protocols PP1-98 and PP2-99, were developed. The approaches followed in these procedures are of great value for the ongoing research on pavement aging; however, due to limited resources and time constraints under the SHRP program, these provisional procedures have certain limitations. A research study, NCHRP Project 9-23, was initiated to overcome these limitations and enhance the predictive capabilities of these protocols. The current research paper is a part of NCHRP 9-23, which deals with the PP1-98 protocol. Binders and field cores were obtained from long-term pavement performance and other sites across the United States. Original, laboratory-aged, and field-aged binders were characterized through dynamic shear rheometer testing. The existing protocol was verified; on the basis of the findings, the protocol was improved to include the effect of field aging conditions and mix properties. The developed model was calibrated and validated with field data. Parametric analysis was performed on the final model to ascertain the practicality of the output. On the basis of those findings, a recommended provisional protocol was developed. The recommendations apply only for conventional, nonmodified binders.
查看更多>>摘要：Antistripping additives and polymer modifications are two common modifiers used to improve the fundamental properties of asphalt binders as those properties relate to the performance of asphalt mixtures. Adhesion and cohesion are two important related properties of asphalt binders that can affect asphalt mixture performance before and after water conditioning. The purpose of this study was to quantify the effects of antistrip-ping additives and polymers on the adhesion and cohesion of binders and to relate these effects to the performance of mixtures as measured in the laboratory before and after water conditioning. The performance tests of asphalt mixtures included indirect tensile strength, uniaxial compression permanent deformation, and Hamburg wheel tracking. Asphalt mixtures were produced with different modified binders and with two aggregate types. The binders were modified with antistripping additives and polymers and by chemical treatment and oxidization methods. Granite and limestone were selected as two types of aggregate sources. The results indicate that the performance of asphalt mixtures is highly dependent on modification techniques and water conditioning. The overall performance of polymer-modified mixtures is more desirable than those of unmodified mixtures and of mixtures modified with antistripping additives. Polymers are found to improve rutting performance, adhesion, and cohesion of an asphalt binder. In contrast, the antistripping additive can improve only the adhesion without changing other properties. The results of this study also illustrate that the adhesion and cohesion of an asphalt binder are good indicators of the performance of asphalt mixtures in the laboratory when they are conditioned with water.
查看更多>>摘要：Rotational viscosities of different asphalt binders were determined at temperatures between 80℃ and 185℃. Viscosity-temperature dependence of asphalt binders was described with the use of the Vogel-Tammann-Fulcher (VTF) and the William-Landel-Ferry (WLF) equations. The Vogel temperature (T_v) and the glass transition temperature (T_g) for different asphalt binders were determined by fitting experimental values of viscosity at different temperatures with these two equations. For asphalt binders, the difference between T_v and T_g was about 40K. Effects of asphaltenes, aging, chemical modification, and polymer content on these temperatures were evaluated. As asphaltene content increased, both temperatures, T_v and T_g, increased. Different polymers showed different effects on these temperatures. The values of T_v and T_g were correlated with the critical cracking temperature (T_(cr)) determined through use of a bending beam rheometer and a direct tension tester. The results suggested that the correlations between T_v, T_g, and T_(cr) could be used to determine T_(cr) from the rotational viscosity results tested at high temperature. With simple rotational measurements, a quick estimation of T_(cr) of asphalt binders could be obtained. Liquid fragility theory was also used to study T_g of asphalt binders. Parameters determined with the VTF and WLF equations indicated that asphalt binders behaved as fragile liquids because of their non-Arrhenius behavior in the temperature range studied.
Mihai O. MarasteanuTimothy ClyneJim McGrawXinjun Li...
p.52-59页
查看更多>>摘要：Previous research efforts have shown that the rutting parameter used in the performance grade asphalt binder specifications, |G~*|/sin δ, does not reasonably predict the rutting potential of asphalt mixtures, especially when modified binders are used. A number of other parameters, such as the zero shear rate viscosity and the permanent strain accumulated under repeated creep and recovery, were investigated; however, no consensus was achieved. This paper investigates the use of zero shear rate viscosity and of repeated creep permanent strain as potential specification parameters and discusses the importance of temperature susceptibility and of strain tolerance to the rut resistance of asphalt binders.
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