| 1. |
- Bayazit, Mehmet, et al.
(author)
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Moisture susceptibility of warm mix asphalt
- 2014
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In: Indian journal of engineering & materials sciences. - 0971-4588 .- 0975-1017. ; 21:6, s. 683-691
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Journal article (peer-reviewed)abstract
- In this study, moisture susceptibility characteristics of wax modified bitumens and warm mix asphalt (WMA) mixtures are determined. The asphalt mixtures are prepared with 50170 penetration grade unmodified bitumen and modified bitumens with three different types of additives (Fischer Tropsch wax, montan wax and polyethylene wax) by weight of 6%. The moisture susceptibility characteristic of the four bitumens is determined with Sessile drop method and that for asphalt mixtures is determined with Nicholson stripping test on loose asphalt mixtures and Modified Lottman test on compacted asphalt mixtures. Furthermore, Marshall stability with different blow numbers of WMA mixtures are determined. The findings from all of these tests suggest that due to the Fischer Tropsch wax and montan wax modification the asphalt mixture become more moisture susceptible which correlates with the surface energy characterization. Interestingly, polyethylene wax modification shows positive moisture performance.
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| 2. |
- Das, Arunita, et al.
(author)
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Particle Swarm Optimizer Variants for Multi-level Thresholding: Theory, Performance Enhancement and Evaluation
- 2024
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In: Archives of Computational Methods in Engineering. - : SPRINGER. - 1134-3060 .- 1886-1784.
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Journal article (peer-reviewed)abstract
- Multilevel thresholding (MLT) has a significant impact in the realm of image segmentation. It is a simple and efficient method for image segmentation. However, as the number of thresholds increases, the computational complexity of MLT increases exponentially, and proper thresholding crucially depends on the utilized objective function. Swarm intelligence (SI) with the optimal objective function is used to enhance the efficacy of MLT image segmentation. Among the various SI techniques, Particle Swarm Optimization (PSO) and its variants are utilized extensively in literature to improve the performance of MLT. As a result, the objective of this study is to provide an updated survey on this topic. This study provides a comprehensive report of the classical PSO, and its improved variants, and their applications in MLT domains. However, like other SI techniques, PSO and its widely utilized variant called Darwinian PSO (DPSO) have the drawbacks of imbalanced exploration and exploitation and premature convergence. Therefore, along with the updated survey report, this study develops an efficient variant of the DPSO called Cauchy DPSO with Opposition Learning (CaDPSOOL). The Cauchy distribution and opposition learning (OL) have been incorporated to enhance the optimization capability by preventing premature convergence and maintaining the good balance between exploration and exploitation. Furthermore, a new hybrid objective function has also been designed by considering Otsu and Tsallis entropy in MLT domain for better segmentation results. The proposed CaDPSOOL with hybrid objective function has been employed for standard color image and hematopathology image segmentation domains. The results of this study show that the proposed model produces better results than other state-of-the-art MLT models in terms of segmentation quality metrics.
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| 3. |
- Das, Prabir Kumar, 1982-
(author)
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Ageing of Asphalt Mixtures : Micro-scale and mixture morphology investigation
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- There are many variables that affect the viscoelastic properties of asphalt mixtures with time, among which age hardening may be considered one of the important ones. Age hardening of asphalt mixtures is an irreversible process, which contributes to a reduction of the durability of pavements and eventually increases the maintenance cost. Beside the environmental effects, ageing in asphalt mixture depends on the physicochemical properties of bitumen and mixture morphology which is a combined effect of aggregate packing, porosity, air void distribution and their interconnectivity. Thus, a clear understanding on the physicochemical properties of bitumen and mixture morphology may help to predict the performance of asphalt mixtures, which will contribute to longer-lasting and better performing pavements.When looking at the bitumen at micro-scale, one can see microstructures appearing under certain conditions which can be partially explained by the interaction of the individual phases. Since the thermo-rheological behavior of bitumen depends largely on its chemical structure and intermolecular microstructures, studying these can lead to understanding of the mechanism, speed and conditions under which this phase behavior occurs. Linking this to the changes in properties of bitumen can thus lead to better understanding of the causes of ageing, its dominant parameters and the resulting diminished mechanical response.To investigate ageing in asphalt pavements, along with physicochemical properties of bitumen one needs to also focus on the influence of mixture morphology. It is known that asphalt mixtures with similar percentages of air-voids can have different morphologies and thus can age differently. Prediction of ageing behavior without considering the influence of mixture morphology may thus lead to erroneous conclusions and non-optimal mix design. Hence, it is important to understand the interplay between the mixture morphology and ageing susceptibility and relate this to the long term mixture performance.The aim of this Thesis was to develop fundamental understanding on ageing in asphalt mixtures that can contribute to the asphalt community moving away from the currently used accelerated ageing laboratory tests and empirical models that can lead to erroneous conclusions.To reach this aim, experimental and numerical micro-scale analyses on bitumen and meso-scale investigations on mixture morphology have been performed which, collectively, allowed for the development of a method for the prediction of asphalt field ageing, incorporating both mixture morphology and micro-scale bitumen mechanisms. For this, first, the mechanisms of surface ageing and diffusion controlled oxidative ageing were identified. Secondly, the influence of mixture morphology on asphalt ageing susceptibility was investigated. Procedures to determine the controlling parameter were then developed and an empirical framework to quantify the long-term field ageing of asphalt mixtures was set-up. For this, a combination of experimental and numerical methods was employed.An extensive experimental study was carried out to understand the fundamental mechanisms behind the micro-structural phase appearance and the speed or mobility at which they change. Atomic Force Microscopy (AFM) was utilized at different temperatures to investigate the phase separation behavior for four different types of bitumen and co-relate it with the Differential Scanning Calorimetry (DSC) measurements. Based on the experimental findings, it was concluded that the observed phase separation is mainly due to the wax/paraffin fraction presence in bitumen (Paper I). A hypothesis was developed of the appearance of a thin film at the specimen surface due to ageing which is creating a barrier, restricting thus the microstructures to float towards the surface. Furthermore, investigation showed that depending on the bitumen and exposure types this surface thin film is water soluble and thus the moisture damage becomes more severe with the ageing of asphalt pavement (Paper II and IV).A new empirical relation to obtain the primary structure coating thickness was established utilizing mixture volumetric properties and gradation using a large set of data from different literature sources. It was found that the enhanced morphological framework can be used to optimize the long term performance of asphalt mixtures (Paper III). Thereafter, the effect of diffusion controlled oxidative ageing on different mixture morphologies based on oxidative ageing mechanism of bitumen and diffusion-reaction process was investigated using the Finite Element Method (FEM). From the FE analyses, the effect of air-void distribution and their interconnectivity combined with the aggregate packing was shown to have a significant effect on age hardening (Paper IV).It was shown that focusing only on the percentage of air-void as the main predictive ageing parameter may lead to an erroneous conclusion and non-optimal predictions of long-term behavior. To replace such approaches, a new way to predict the long-term ageing was proposed in this Thesis, utilizing the found influences of mixture morphology and fundamental mechanism. Though additional mechanisms and non-linear coupling between them may be still needed to reach the ‘ultimate’ ageing prediction model, the current model was found to be a significant improvement to the currently used methods and may lead the way towards further enhancing the fundamental knowledge towards asphalt mixture ageing (Paper V).
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| 4. |
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| 5. |
- Das, Prabir Kumar, et al.
(author)
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Atomic force microscopy to investigate asphalt binders : a state-of-the-art review
- 2016
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In: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 17:3, s. 693-718
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Journal article (peer-reviewed)abstract
- Atomic force microscopy (AFM) is a non-destructive imaging tool, which is capable of qualitative and quantitative surface analysis with sub-nanometer resolution. Simultaneously with the topology at the micro-scale, AFM is capable of acquiring micro-mechanical information such as relative stiffness/Young's modulus, stickiness/adhesion, hardness, energy loss and sample deformation quantitatively. This paper presents an extensive review on the applications of AFM to investigate different physiochemical properties and performances of asphalt binder. AFM techniques and principles, different sample preparation techniques and its effect on observed micro-structures, chemical origin, surface or bulk phenomenon and temperature sensitivity of these micro-structures are also discussed in this paper. All of the studies conducted on this topic clearly indicated that AFM can successfully be utilised as a tool to better understand how the surface morphology and its physicochemical properties are interlinked and related to the binder performances.
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| 6. |
- Das, Prabir Kumar, et al.
(author)
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Coupling of oxidative ageing and moisture damage in asphalt mixtures
- 2015
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In: International Journal on Road Materials and Pavement Design. - : Informa UK Limited. - 1468-0629 .- 2164-7402. ; 16, s. 265-279
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Journal article (peer-reviewed)abstract
- In this paper, a possible way to capture the combined effect of oxidative ageing and moisture damage on mixture performance has been proposed. The formulations that are needed for finite element (FE) modelling of oxygen and moisture diffusion process have been established. The proposed model should be able to link the in-time changes to the mastic as function of mixture morphology, ageing propensity and the moisture diffusion properties to the physical properties of the asphalt mixture due to the loss of adhesive and/or cohesive bonding. Such an FE model can help find the trends and relationships that can assist in the development of predictive pavement performance model. Also, from this, one can figure out the key parameters that are mainly responsible for ageing-moisture-induced premature damage of asphalt pavements.
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| 7. |
- Das, Prabir Kumar, et al.
(author)
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Evaluation of fracture and moisture damage performance of wax modified asphalt mixtures
- 2012
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In: International Journal on Road Materials and Pavement Design. - : Informa UK Limited. - 1468-0629 .- 2164-7402. ; 13:1, s. 142-155
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Journal article (peer-reviewed)abstract
- In this study the fracture and moisture damage characteristics of wax modified asphalt mixtures were evaluated. Two types of commercial waxes (FT-paraffin and Asphaltan B) were added to bitumen of penetration grade 70/100. Using this wax modified and unmodified bitumen; total 48 specimens were produced from two sources of aggregates and two levels of gradation. Bitumen properties were determined by conventional test methods, Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) testing. Thermal Stress Restrained Specimen Test (TSRST) was used to evaluate low temperature cracking resistance and cracking behavior of asphalt mixture was investigated at 0 degrees C using Superpave Indirect Tensile Test (IDT). The influence of wax on the asphalt mixture resistance to cracking and moisture damage performance has been evaluated using Hot Mix Asphalt (HMA) fracture mechanics and Superpave IDT test results. The addition of FT-paraffin and Asphaltan B showed better cracking and moisture damage resistance of the asphalt mixture compared to unmodified mixture, but FT-paraffin showed the largest effect on cracking resistance while Asphaltan B showed highest resistance to moisture damage. In BBR test results, mixtures modified with FT-paraffin showed lower limit m value (LmT) which implies minor negative effect in stress relaxation. However, according to TSRST results, the mixtures with both waxes had nearly same fracture temperature as mixture with unmodified bitumen.
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| 8. |
- Das, Prabir Kumar, 1982-, et al.
(author)
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Evaluation of the low temperature cracking performance of asphalt mixtures utilizing HMA fracture mechanics
- 2013
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In: Construction and Building Materials. - : Elsevier. - 0950-0618 .- 1879-0526. ; 47, s. 594-600
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Journal article (peer-reviewed)abstract
- In the present study, the low temperature cracking performance of asphalt mixture has been investigated numerically and experimentally. To do so, the HMA thermal fracture model has extended by including fracture energy threshold and non-linear thermal contraction coefficient. This extended model is capable to predict thermally induced stress and fracture temperature, which is validated with experimental results obtained from three different types of asphalt mixtures. From the parametric study, it was observed that understanding the influence of thermal contraction coefficient, the cooling rate and the creep compliance parameters can make a significant contribution to the material's sustainability. From the analysis, it was found that this extended model can be utilized to evaluate the low temperature cracking performance of asphalt mixtures and capable to provide correct ranking. Interestingly, non-linear thermal contraction coefficient gave much better prediction than linear approach.
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| 9. |
- Das, Prabir Kumar, et al.
(author)
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Investigation of the asphalt mixture morphology influence on its ageing susceptibility
- 2015
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In: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:4, s. 987-1000
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Journal article (peer-reviewed)abstract
- The main objective of this study is to investigate the influence that asphalt mixture morphology aspects have on its overall ageing behavior. Since mixture morphology is controllable, having insight into how the various morphological parameters influence the mixture’s long-term behavior can be of great value to optimize its design, regardless of the individual material properties. To do so, this study is utilizing a new framework to characterize the combined effect of aggregate packing, average air void size, porosity and level of compaction on ageing for a large set of data from different sources of field compacted and laboratory produced asphalt mixtures. The paper also hypothesizes about the mechanisms that lay behind the found influences and how thus mixture design improvements can be made. From all the investigated cases, it was found that the framework can be used to optimize the durability performance of asphalt mixtures. It was also observed that prediction of ageing behavior without considering the influence of mixture morphology may lead to erroneous conclusions and non-optimal mix design.
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| 10. |
- Das, Prabir Kumar, et al.
(author)
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Low temperature cracking performance of WMA with the use of the Superpave indirect tensile test
- 2012
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In: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 30, s. 643-649
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Journal article (peer-reviewed)abstract
- Low temperature cracking of wax modified bitumen and asphalt mixtures were studied using the Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), Superpave IDT and Thermal Stress Restrained Specimens Test (TSRST). Two types of commercial waxes (FT-paraffin and Asphaltan-B) were added to 70/100 penetration grade bitumen. Hot Mix Asphalt (HMA) fracture mechanics was used to determine fracture parameters. Master curves obtained from DSR and BBR test results showed stiffening effect due to wax additive at low temperature. The analysis of covariance was performed using a General Linear Model (GLM) on the Superpave IDT test results for Energy Ratio (ER) by using SPSS (Statistical Program for Social Sciences). Statistical analysis of Superpave IDT results showed a minor negative effect of wax modification at lower temperatures. Statistical analysis also showed that fracture parameters are highly temperature dependent and the two types of aggregate used did not play any significant role in low temperature cracking performance. Results obtained from TSRST tests indicate wax modification has a minor negative effect in low temperature cracking performance of asphalt mixtures.
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| 11. |
- Das, Prabir Kumar, et al.
(author)
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Micro-Mechanical Investigation of Low Temperature Fatigue Cracking Behaviour of Bitumen
- 2012
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In: 7th RILEM International Conference on Cracking in Pavements. - Dordrecht : Springer Netherlands. - 9789400745650 ; , s. 1281-1290
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Conference paper (peer-reviewed)abstract
- In an effort to understand the effect of low temperature fatigue cracking, atomic force microscopy (AFM) was used to characterize the morphology of bitumen. In addition, thermal analysis and chemical characterization was done using differential scanning calorimetry (DSC) and thin-layer chromatography/flame ionization detection (TLC/FID), respectively. The AFM topographic and phase contrast image confirmed the existence of bee-shaped microstructure and different phases. The bitumen samples were subjected to both environmental and mechanical loading and after loading, micro-cracks appeared in the interfaces of the bitumen surface, confirming bitumen itself may also crack. It was also found that the presence of wax and wax crystallization plays a vital role in low temperature cracking performance of bitumen.
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| 12. |
- Das, Prabir Kumar, et al.
(author)
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Micro-scale investigation of oxygen diffusion on bitumen surfaces
- 2014
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In: Asphalt Pavements - Proceedings of the International Conference on Asphalt Pavements, ISAP 2014. - : CRC Press. - 9781315736754 - 9781138026933 ; , s. 935-942
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Conference paper (peer-reviewed)abstract
- This study investigates the evolution of microstructures due to oxygen diffusion on bitumen surface and its effect on bulk properties utilizing Atomic Force Microscopy (AFM) and Differential Scanning Calorimetry (DSC). The bitumen specimens were conditioned in four different modes: both light and air, only air but no light, only light but no air and neither light nor air, for 15 and 30 days. From the AFM investigation after 15 and 30 days of conditioning period, it was found that the percentages of microstructure on the surface reduced with ageing. The DSC heating scan showed that the amount of wax remains constant even after the systematic conditioning. Interestingly, during the cooling cycle, crystallization of wax molecules started earlier for the oxidized specimens than the non-oxidized one. The analysis of the obtained results indicated that the oxidation created a thin film upon the exposed surface, which acts as a barrier and creates difficulty for the wax induced microstructures to float up at the surface. From the DSC analysis, it can be concluded that the oxidation product induced impurities in the bitumen matrix, which acts as a promoter in the crystallization process.
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| 13. |
- Das, Prabir Kumar, et al.
(author)
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Micromechanical investigation ofphase separation in bitumen bycombining atomic force microscopywith differential scanning calorimetryresults
- 2013
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In: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 14:S1, s. 25-37
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Journal article (peer-reviewed)abstract
- The thermo-rheological behaviour of bitumen depends largely on its chemical structure and intermolecular microstructures. Bitumen is a complex mixture of organic molecules of different sizes and polarities for which the micro-structural knowledge is still rather incomplete. Knowledge at that level can have great implications for behaviour at a larger scale and will help to optimise the bitumen in its production stage. The present study is focused on understanding the fundamental mechanisms behind the micro-structural phase appearance and the speed or mobility at which they change. To do so, atomic force microscopy was utilised at different temperatures to investigate the phase separation behaviour for four different types of bitumen and co-relate it with the differential scanning calorimetry measurements. Based on the experimental evidences, it was found that the observed phase separation is mainly due to the wax/paraffin fraction presence in bitumen and that the investigated bitumen behaves quite differently. Recommendations are made to continue this research into qualitative information to be used on the asphalt mix design level.
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| 14. |
- Das, Prabir Kumar, et al.
(author)
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Microscale investigation of thin film surface ageing of bitumen
- 2014
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In: Journal of Microscopy. - : Wiley. - 2050-5698 .- 0022-2720 .- 1365-2818. ; 254:2, s. 95-107
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Journal article (peer-reviewed)abstract
- This paper investigates the mechanism of bitumen surface ageing, which was validated utilizing the atomic force microscopy and the differential scanning calorimetry. To validate the surface ageing, three different types of bitumen with different natural wax content were conditioned in four different modes: both ultraviolet and air, only ultraviolet, only air and without any exposure, for 15 and 30 days. From the atomic force microscopy investigation after 15 and 30 days of conditioning period, it was found that regardless the bitumen type, the percentage of microstructure on the surface reduced with the degree of exposure and time. Comparing all the four different exposures, it was observed that ultraviolet radiation caused more surface ageing than the oxidation. It was also found that the combined effect was not simply a summation or multiplication of the individual effects. The differential scanning calorimetry investigation showed that the amount of crystalline fractions in bitumen remain constant even after the systematic conditioning. Interestingly, during the cooling cycle, crystallization of wax molecules started earlier for the exposed specimens than the without exposed one. The analysis of the obtained results indicated that the ageing created a thin film upon the exposed surface, which acts as a barrier and creates difficulty for the wax induced microstructures to float up at the surface. From the differential scanning calorimetry analysis, it can be concluded that the ageing product induced impurities in the bitumen matrix, which acts as a promoter in the crystallization process.
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| 15. |
- Das, Prabir Kumar, et al.
(author)
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Numerical study on the effect of mixture morphology on long-term asphalt mixture ageing
- 2015
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In: The international journal of pavement engineering. - : Informa UK Limited. - 1029-8436 .- 1477-268X. ; 16:8, s. 710-720
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Journal article (peer-reviewed)abstract
- Asphalt mixtures with similar percentages of air voids can have different morphologies and can age differently. Prediction of ageing behaviour without considering the influence of mixture morphology may thus lead to erroneous conclusions and non-optimal mix design. This article investigates the long-term field ageing of asphalt mixtures by incorporating mixture morphology. For this, a computational analysis on diffusion-reaction process has been conducted by implementing fundamental mechanism of ageing and conducting a parametric sweep of the morphology. To investigate the ageing gradient along the depth of asphalt mixture, diffusion controlled oxidative ageing on one dense and one open-graded field core was investigated. The proposed model based on the mixture morphology information was able to predict the aged viscosity better than the existing model. As mixture morphology is controllable, having insight into how the morphology parameter influences the mixture's ageing susceptibility can be of great value to its design.
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| 16. |
- Das, Prabir Kumar, et al.
(author)
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On the Oxidative Ageing Mechanism and Its Effect on Asphalt Mixtures Morphology
- 2015
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In: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 48:15, s. 3113-3127
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Journal article (peer-reviewed)abstract
- This paper investigates the influence of mixture morphologies and microstructures on oxidative ageing of asphalt mixtures. For this, an oxidative ageing mechanism based on a diffusion–reaction process was developed. Previously, most asphalt oxidative ageing modeling research focused on unidirectional diffusion of continuous oxygen flow through bitumen films, which is far from the actual boundary conditions in asphalt mixtures. For this reason in the current study, a finite element (FE) analysis has been conducted in which 3D mixture morphology was considered. Mixture morphology is the combination of mineral aggregate packing, porosity, air-void distribution and their interconnectivity. One dense and one open graded field asphalt mixture core were scanned with a computerized tomography X-ray scanner. In the analyses, the developed oxidative ageing model was implemented. The FE analysis showed that the effect of the air-void distribution, their interconnectivity and the mineral aggregate packing has a significant effect on the resulting age hardening of the overall mixture. Furthermore, from the microstructural investigation done in this research, strong indications were found that, depending on the bitumen and its conditioning, water soluble thin films are formed due to ageing. This means that ageing and moisture damage are strongly interlinked and this should thus be considered in the design of the asphaltic materials and the prediction of their long term performance.
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| 17. |
- Das, Prabir Kumar, 1982-
(author)
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Thermally Induced Fracture Performance of Asphalt Mixtures
- 2012
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Licentiate thesis (other academic/artistic)abstract
- A major distress mode in asphalt pavements is low temperature cracking, which results from the contraction and expansion of the asphalt pavement under extreme temperature changes. The potential for low temperature cracking is an interplay between the environment, the road structure and importantly the properties of the asphalt mixture. The thermal cracking performance of asphalt concrete mixtures can be evaluated by conducting thermal stress restrained specimen tests (TSRST) which is known to be correlated well with the fracture temperatures observed in the field. Although TSRST provides a good estimation of the field performance, it may be unrealistic to implement the obtained results in a design framework. On the other hand, recent studies showed Superpave indirect tension tests can be used to evaluate fracture performance (fatigue, moisture damage, low temperature cracking, etc.) of the asphalt concrete mixtures. In addition, the obtained elastic and viscoelastic parameters from the Superpave IDT tests can be used as an input parameter to establish a design framework. The study presented in this thesis has a main objective to develop a framework using Superpave IDT test results as input parameters in order to evaluate the low temperature cracking performance of asphalt concrete mixtures. Moreover, the study aims to investigate micro-mechanically the low temperature cracking behavior of bitumen using atomic force microscopy (AFM) as a tool.The numerical model has been developed by integrating fracture energy threshold into an asphalt concrete thermal fracture model, considering non-linear thermal contraction coefficients. Based on the asphalt concrete mixture viscoelastic properties, this integrated model can predict thermally induced stresses and fracture temperatures. The elastic, viscoelastic and fracture energy input parameters of the model were measured by conducting indirect tension tests and the thermal contraction coefficients were measured experimentally. The proposed model has been validated by comparing the predicted fracture temperatures with the results obtained from TSRST tests. It was found that, while there is a quantitative discrepancy, the predicted ranking was correct. In the measurement of the thermal contraction coefficients it was observed that the thermal contraction coefficient in asphalt concrete is non-linear in the temperature range of interest for low temperature cracking. The implications of having non-linear thermal contraction coefficient were investigated numerically.In an effort to understand the effect of bitumen properties on low temperature fatigue cracking, AFM was used to characterize the morphology of bitumen. The AFM topographic and phase contrast image confirmed the existence of bee-shaped microstructure and different phases. The bitumen samples were subjected to both environmental and mechanical loading and after loading, micro-cracks appeared in the interfaces of the bitumen surface, confirming bitumen itself may also crack. It was also found that the presence of wax and wax crystallization plays a vital role in low temperature cracking performance of bitumen.
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| 18. |
- Das, Prabir Kumar, et al.
(author)
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Towards a Multi-scale Framework to Optimize Ageing Resistance of Asphaltic Materials
- 2013
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In: Multi-Scale Modeling and Characterization of Infrastructure Materials. - Dordrecht : Springer Netherlands. - 9789400768772 - 9789400768789 ; , s. 285-295
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Conference paper (peer-reviewed)abstract
- This paper describes an ongoing research project that is aiming at developing a comprehensive multi-scale approach to optimize the ageing resistance of asphaltic mixtures. In this, ageing has been focused on oxidative ageing, but allows future extension to other ageing mechanisms. The developed framework considers three different scales: the nano, micro and meso-scale which are defined as the bitumen phase, the mastic phase and the mixture phase, respectively. In nano-scale, atomic force microscopy and calorimetry are coupled to each other to give insight into how bitumen phase separation evolves and the mobility of microstructure changes with temperature and ageing. On the micro-scale, the energy dissipation as a function of ageing is measured and coupled to the phase behavior information from the nano-scale. On the meso-scale a morphology framework is defined, capable of identifying the dominant mixture morphology parameters that control mixture performance under ageing conditions. By coupling the three scales, the dominant parameters that control ageing of asphaltic mixtures can be defined, modeled and analyzed and as such a tool is created that has the potential of enhancing the sustainability of asphaltic mixtures.
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| 19. |
- Fischer, Hartmut, et al.
(author)
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Challenges While Performing AFM on Bitumen
- 2013
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In: Multi-Scale Modeling and Characterization of Infrastructure Materials. - Dordrecht : Springer Netherlands. - 9789400768772 - 9789400768789 ; , s. 89-98
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Conference paper (peer-reviewed)abstract
- Using modern microscopic techniques such as atomic force microscopy (AFM) has added significant knowledge on the microstructure of bitumen. The advantages of AFM are that it requires relatively simple sample preparation and operates under ambient conditions. As the use of AFM is becoming more widespread and useful the RILEM technical committee (TC) on nano bituminous materials NBM 231 has conducted a round robin study on this method, the results with respect to reproducibility, repeatability or accuracy limits are presented elsewhere. However, the execution of good quality AFM experiments especially on bitumen is still a challenging task. Sample extraction and preparation are very crucial and attention should be paid to obtain homogenous samples with a sufficient thickness and no surface contamination. The preparation should include a high temperature treatment to provide a smooth homogenous surface. Annealing/resting of the sample has to be sufficiently long, at least 24 h under ambient temperatures to ensure the formation of a (meta)stable micro-structure. Imaging should be done using non-contact (Tapping) mode with stiff cantilevers (resonance frequency ~300 kHz) with a minimum amount of damping as possible.
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| 20. |
- Soenen, Hilde, et al.
(author)
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Differential Scanning Calorimetry Applied to Bitumen : Results of the RILEM NBM TG1 Round Robin Test
- 2013
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In: Multi-Scale Modeling and Characterization of Infrastructure Materials. - Dordrecht : Springer Netherlands. - 9789400768772 - 9789400768789 ; , s. 311-323
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Conference paper (peer-reviewed)abstract
- The application of Differential Scanning Calorimetry (DSC) has been proven useful in characterizing bituminous binders, distillates and crude oils. In this paper, results of the round robin test, organized by the Rilem TC 231 Nanotechnology-based Bituminous Materials (NBM) TG1 group are reported. The purpose is to investigate the repeatability and reproducibility of standard DSC measurements when applied to bituminous binders. In the full test program of the Rilem NBM group, DSC measurements are further compared to observations made in atomic force microscopy (AFM), AFM measurements are reported in a separate paper. Seven laboratories have participated in this round robin test. Four bituminous binders were investigated, containing various amounts of natural or added wax. The test program consisted of a well-defined isothermal annealing procedure, followed by a first heating and cooling scan, and afterwards followed by a second heating scan. At this stage, the data, as they were reported by the different participants, were compared. For the glass transition (Tg), mid temperatures, can be defined with a reasonable reproducibility, which improves if natural wax is not present. Regarding melting and crystallization, the shape of the melting curve is highly dependent on the thermal history of the samples. Peak temperatures of melting and crystallization phenomena were reported with a good reproducibility, while the reproducibility of melting enthalpies (or surface area’s under the melting and crystallization signals) was not satisfactory. Different reasons for this and recommendations for improving the results are discussed in the paper.
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| 21. |
- Soenen, Hilde, et al.
(author)
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Laboratory investigation of bitumen based on round robin DSC and AFM tests
- 2014
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In: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 47:7, s. 1205-1220
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Journal article (peer-reviewed)abstract
- In the past years a wide discussion has been held among asphalt researchers regarding the existence and interpretation of observed microstructures on bitumen surfaces. To investigate this, the RILEM technical committee on nano bituminous materials 231-NBM has conducted a round robin study combining differential scanning calorimetry (DSC) and Atomic Force Microscopy (AFM). From this, methods for performing DSC and AFM tests on bitumen samples and determination of the influence of wax on the observed phases, taking into account thermal history, sample preparation and annealing procedure, are presented and critically discussed. DSC is used to measure various properties and phenomena that indicate physical changes such as glass transition temperature (T (g)) and phase transition such as melting and crystallization. In the case of existence of wax, either natural or synthetic, it can further indicate the melting point of wax, that could be used to determine wax content. The results from seven laboratories show that T (g) temperatures obtained from the heating scans are more repeatable and easier to obtain in comparison to the cooling scans. No significant difference was noted for T (g)'s obtained from the first and second heating scans. AFM is an imaging tool used to characterize the microstructures on a bituminous surface. Using AFM three phases in the materials with wax could be distinguished. The changes in the phases observed with AFM for increases in temperature were correlated with the DSC curve, and it could be established that the so called "Bee" structure disappeared around the melting peak in the DSC curve. Thus, this research has confirmed the relation between the microstructures on a bitumen surface and the wax content.
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