| 1. |
- Bjorklund, Robert, et al.
(författare)
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Photodesorption of fulvic acid from iron oxide surfaces into aqueous solutions
- 2001
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 174:2, s. 166-175
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Tidskriftsartikel (refereegranskat)abstract
- Photodesorption of thin films of fulvic acid adsorbed on planar iron oxide surfaces was monitored by ellipsometry. Description was first observed at 546 nm, and additional fractions of the adsorbed acid left the surfaces at 405 and 365 nm Similar kinetics for photodesorption was observed from metallic iron films and from porous iron oxide prepared electrochemically by deposition on porous silicon substrates. Soluble photoproducts leaving the surface H ere monitored by UV absorbance spectroscopy at 200 nm Gaseous products were not detected by mass spectrometry but the results seemed to indicate that net all of the photoproducts entered the liquid phase. Of the metal films tested which adsorbed fulvic acid from aqueous solution (Fe. Cr, Ni, Al, and Pt), it was only iron which exhibited a photodesorption effect. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 2. |
- Di Benedetto, H, et al.
(författare)
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Fatigue of bituminous mixtures
- 2004
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Ingår i: Materials and Structures. - 1359-5997 .- 1871-6873. ; 37:267, s. 202-216
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an interlaboratory test campaign organized by the RILEM 182-PEB Technical Committee. In the campaign, 11 different test methods, comprising uniaxial tension/compression, 2-, 3- and 4-point bending and indirect-tension tests, were utilized in order to investigate fatigue characteristics of a dense graded asphalt concrete mixture. The testing conditions specified were sinusoidal excitation at 10Hz and 10degreesC using controlled strain and stress modes. In total, more than 150 fatigue tests were carried out during the investigation. The fatigue test results were analyzed using both classical as well as continuum damage mechanics approaches. The fatigue test results obtained using the classical fatigue approach are considerably influenced by test type and mode of loading (controlled stress or strain) used. Consequently, this approach has limited use in realistic fatigue characterization of bituminous materials and pavement structures. In contrast to the classical approach, models founded on continuum damage theory may serve to isolate intrinsic fatigue characteristics from the influence of so-called biased effects, which are largely caused by the accelerated laboratory testing. The continuum damage models investigated may constitute steps, towards a rational mechanistic fatigue characterization model, which are important for effective future pavement design.
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| 3. |
- Lundström, Robert, et al.
(författare)
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An investigation of the applicability of Schapery's work potential model for characterization of asphalt fatigue behavior
- 2004
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Ingår i: 2004 Journal Of The Association Of Asphalt Paving Technologists. ; , s. 657-695
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Konferensbidrag (refereegranskat)abstract
- This paper presents an investigation of Schapery's work potential model applied to asphalt concrete characterization. Six asphalt concrete mixtures, all consisting of one and the same aggregate and particle size distribution, manufactured using unmodified and SBS modified binders were used. An elastic-viscoelastic correspondence principle and the time-temperature superposition principle are utilized to obtain material characteristic functions, C-1(S-1), using uniaxial monotonic (constant-strain rate) and cyclic (fatigue) tests at 0, 10 and 20C. The results indicate that consistent and reliable results are obtained for the mixtures investigated using monotonic testing, provided that the applied strain rate is not too low at a given temperature. It was also indicated that the time-temperature superposition principle is applicable as a single material function can be obtained at the reference temperature chosen. Results similar to those obtained at monotonic tests were also obtained at cyclic testing. However, based on statistical analysis, it was noticed that cyclically established C-1(S-1) curves often differ slightly between different temperatures even when shifted to the reference temperature. This result is probably due to the more complicated excitation history applied during fatigue tests. However, even though it is possible to obtain characteristic material functions from both types of tests, it was not possible to show that monotonic and cyclic testing lead to similar results, i.e. more or less identical C-1(S-1) curves. It was also investigated, using thermocouples, whether, and if so, to what extent hysteretic self-heating influences fatigue test results. In general, a significant influence was indicated at 10 and 20C, and especially for high amplitude tests (low cycle fatigue tests). Even though several questions still are to be answered, the model based on the work potential theory remains interesting, and is possibly, the most versatile damage model for asphalt characterization available today.
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| 4. |
- Lundström, Robert, et al.
(författare)
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Influence of asphalt mixture stiffness on fatigue failure
- 2004
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Ingår i: Journal of materials in civil engineering. - 0899-1561 .- 1943-5533. ; 16:6, s. 516-525
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Tidskriftsartikel (refereegranskat)abstract
- This paper examines the question of an appropriate failure criterion for asphalt fatigue characterization. The results presented are based on cyclic fatigue tests and obtained from three mixtures containing different penetration grade bitumens from one and the same source. The mixtures are tested at 0, 10, and 20degreesC using uniaxial testing (tension/compression) on cylindrical samples. It is found that failure can be demonstrated by studying the evolution of the strain field using three parallel extensometers (separated by 120degrees around the specimen). The failure arises from coalescence of microcracks (damage localization). The decrease in stiffness at failure is related to mixture stiffness, where stiff materials (low temperature and/or mixtures containing low pen grade binder) show comparatively small decrease. A statistical approach based on fatigue tests carried out at different temperatures is suggested, an approach which uses stiffness degradation as a measure of critical fatigue stiffness. The advantage of such a failure criterion compared to the classical failure criterion (decrease in stiffness by 50%) for different temperatures is discussed. Using the proposed criterion, higher consistency in results is achieved compared to results obtained using the classical failure criterion.
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| 5. |
- Lundström, Robert, et al.
(författare)
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Influence of hysteretic heating on asphalt fatigue characterization
- 2004
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Ingår i: Journal of Testing and Evaluation. - 0090-3973 .- 1945-7553. ; 32:6, s. 484-493
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study focusing on the influence of hysteretic heating on asphalt samples during laboratory fatigue testing. The experimental test setup for material characterization and temperature measurements, including its effect on fatigue test results, as well as theoretical aspects on hysteretic heating, are described. The experimental part of the investigation concerns linear viscoelastic and cyclic fatigue characterization of six asphalt concrete mixtures using uniaxial testing. All the mixtures show nominally identical volumetric properties (aggregate size distribution, binder and air void content) but different binder properties. Three base bitumens and three polymer modified binders were used. The cyclic fatigue tests were carried out at 0, 10, and 20 C using controlled strain and stress modes and different excitation amplitudes. In order to acquire knowledge regarding temperature changes during fatigue testing, several experimental techniques were used. The main thermal study was performed using thermocouples attached to the midheight envelope surface of each sample. The sample surface temperature distribution and its evolution during fatigue testing were investigated using an infrared thermal camera. Furthermore, a limited study of the magnitude of difference between surface and maximum temperature inside the sample was carried out using thermocouples embedded during gyratory compaction. When compared, each method shows advantages and disadvantages regarding simplicity and reliability. In principle, the three methods provide similar results, but the type of information obtained differs among the methods. The use of thermocouples attached to the envelope surface during fatigue testing provides accurate and consistent results of global temperature that can be used to investigate the influence of heating on asphalt fatigue characteristics. By use of thermal measurements and a continuum damage model, it was possible to show a pronounced effect of heating on fatigue behavior. The influence of heating was especially obvious at high excitation amplitudes and elevated temperatures, i.e., conditions where the material produces high amounts of viscoelastic dissipated energy as well as temperature sensitive material behavior.
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| 6. |
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| 7. |
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| 8. |
- Testorf, Martin, et al.
(författare)
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Characterization of [3H]flunitrazepam binding to melanin
- 2001
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Ingår i: Analytical Biochemistry. - : Elsevier BV. - 0003-2697 .- 1096-0309. ; 298:2, s. 259-264
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Tidskriftsartikel (refereegranskat)abstract
- In both clinical and forensic toxicology, the analysis of hair for drugs is an important tool to determine drug use in the past or to verify abstinence from illegal drugs during extended periods. Melanin is proposed as one of the factors that influences drug incorporation to hair and we have characterized the binding of the drug flunitrazepam to melanin in vitro. The drug was 3H labeled and melanin granules from cuttlefish, Sepia officinalis, were used according to the suggested standard for melanin studies. We observed a rapid Langmuir-like binding followed by a slower diffusion-limited binding that may be interpreted as an initial surface binding followed by deeper bulk binding. From three concentrations of melanin, with a 60-min incubation time, a mean saturation value of 180 ± 20 pmol/mg was calculated. The binding of a group of benzodiazepines and tranquilizers was compared to the binding of [3H]flunitrazepam by means of displacement experiments. These drugs showed binding characteristics similar to [3H]flunitrazepam except phenobarbital, which had a lower affinity to melanin. The method presented in this study allowed measurements with low melanin and drug concentrations and it has the strength of directly measuring the amount of drug bound to melanin, in contrast to previous indirect methods.
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