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  • 1.
    Guarin, Alvaro
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Khan, Abdullah
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Butt, Ali Azhar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Birgisson, Björn
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Aston University School of Engineering and Applied Science, Aston Triangle, Birmingham, United Kingdom.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    An extensive laboratory investigation of the use of bio-oil modified bitumen in road construction2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 106, p. 133-139Article in journal (Refereed)
    Abstract [en]

    Several roads in Iceland with bio-oil modified surface dressings exhibited severe distresses such as bleeding, binder drain down, and eventually as surface dressing sticking to tires. Samples from six road sections were evaluated in the laboratory to determine the causes of the failure. Binders with and without bio-oil, rapeseed oil and fish oil, were evaluated through a comprehensive rheological and chemical characterization. Both oils, exhibited solubility issues with the bitumen; consequently, the oils covered the aggregates, preventing bonding between binder and stones. It appears that fish oil worked a little better than rapeseed oil for binder modification.

  • 2.
    Khan, Abdullah
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Fundamental investigation to improve the quality of cold mix asphalt2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Cold mix asphalt (CMA) emulsion technology could become an attractive option for the road industry as it offers lower startup and equipment installation costs, energy consumption and environmental impact than traditional alternatives. The adhesion between bitumen and aggregates is influenced by diverse parameters, such as changes in surface free energies of the binder and aggregates or the presence of moisture or dust on the surface of aggregates, mixing temperatures, surface textures (including open porosity), nature of the minerals present and their surface chemical composition, as well as additives in the binder phase. The performance of cold asphalt mixtures is strongly influenced by the wetting of bitumen on surfaces of the aggregates, which is governed by breaking and coalescence processes in bitumen emulsions. Better understanding of these processes is required. Thus, in the work this thesis is based upon, the surface free energies of both minerals/aggregates and binders were characterized using two approaches, based on contact angles and vapor sorption methods. The precise specific surface areas of four kinds of aggregates and seven minerals were determined using an approach based on BET (Brunauer, Emmett and Teller) theory, by measuring the physical adsorption of selected gas vapors on their surfaces and calculating the amount of adsorbed vapors corresponding to monolayer occupancy on the surfaces. Interfacial bond strengths between bitumen and aggregates were calculated based on measured surface free energy components of minerals/aggregates and binders, in both dry and wet conditions.

    In addition, a new experimental method has been developed to study bitumen coalescence by monitoring the shape relaxation of bitumen droplets in an emulsion environment. Using this method, the coalescence of spherical droplets of different bitumen grades has been correlated with neck growth, densification and changes in surface area during the coalescence process. The test protocol was designed to study the coalescence process in varied environmental conditions provided by a climate-controlled chamber. Presented results show that temperature and other variables influence kinetics of the relaxation process. They also show that the developed test procedure is repeatable and suitable for studying larger-scale coalescence processes. However, possible differences in measured parametric relationships between the bitumen emulsion scale and larger scales require further investigation.

    There are several different research directions that can be explored for the continuation of the research presented in this thesis. For instance, the rationale of the developed method for analyzing coalescence processes in bitumen emulsions rests on the assumption that the results are applicable to large-scale processes, which requires validation. A linear relationship between the scales is not essential, but it is important to be able to determine the scaling function. Even more importantly, qualitative effects of the investigated parameters require further confirmation. To overcome the laboratory limitations and assist in the determination of appropriate scaling functions further research could focus on the development of a three-dimensional multiphase model to study coalescence processes in more detail, including effects of surfactants, pH and other additives such as mineral fillers and salts. Additionally, better understanding of the breaking process and water-push out could help significantly to optimize CMA mix design. Different methods, both numerical and experimental could be explored for this.

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  • 3.
    Khan, Abdullah
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Towards the enhanced applicability of cold mix asphalt:: An experimental study focusing on surface free energies and the breaking and coalescence of bitumen emulsions2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The environmental, social and economic sustainability of our infrastructure network is clearly of paramount importance to the road-engineering sector as well to society at large. Sustainable road materials and reduced transport of those materials therefore play a significant role. Cold mix asphalt (CMA) emulsion technology could be one of the better options for the road industry to explore more thoroughly. Given its lower start-up and equipment installation costs, lower energy consumption and reduced environmental impact, CMA should offer a reliable alternative to some of the Hot Mix Asphalt (HMA) or Warm Mix Asphalt (WMA) options. As CMA is not a new technology, there are many reasons why this material is not currently being used as extensively as it might be. Though risk adverseness of the market may be partly to blame for this, a number of technical challenges and uncertainties related to material behavior are certainly responsible. This thesis has addressed some of the important technical challenges, aiming to provide more guidance in material selection and design, and prediction of the behavior of emulsion-based CMAs. To do so, this research has focused on aspects of the correct formulation of the bitumen emulsions, how to select the correct combinations of material components, and how to control the breaking and coalescence processes in bitumen emulsions better, resulting in usable and predictable adhesive and cohesive bond strengths. Though most of the laboratory and modeling choices that were made in this thesis are based on theoretical considerations, the main contribution is the test protocol development. The systematic surface free energy measurements of the material components, combined with the test set-up to monitor controllably the breaking and coalescence behavior of bitumen droplets in an emulsified environment, gives a new way to approach the design of CMA. It is recommended that future research is focused on taking the developed protocols as a basis for enhanced mix design and making a direct link to validated long-term mechanical properties on the asphalt mixture scale.

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  • 4.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Balieu, Romain
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Architectural Technologies. KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Redelius, Per
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Modelling coalescence process during breaking of bitumen emulsions2016In: / [ed] International Society for Asphalt Pavements (ISAP), 2016, p. 1-12, article id Paper 61Conference paper (Refereed)
    Abstract [en]

    Cold mix bitumen emulsion technology is getting a lot of focus by the road industries since a few decades due to the diminished environmental impacts and reduced energy associated with it. The durability and mechanical performance of cold asphalt mixtures very much depend on the breaking, coalescence and phase separation processes in bitumen emulsions; however, the exact nature of the breaking mechanism of bitumen emulsion is not completely understood today. During coalescence or relaxation process, two bitumen droplets are completely fused into a unique spherical droplet and their kinetic is usually recorded in terms of time, denoted as relaxation time or τrelaxation.  In this work, a two dimensional Phase Field model was used to simulate the coalescence process of two bitumen droplets in water phase. The numerical model is based on Finite Element Method and solves Navier-Stokes system of equations coupled with the Cahn-Hilliard equation. The model predictions are validated by direct comparison with the experimental measurements performed in our previous work. Moreover, the study was extended to the small size (order μm) bitumen droplets which are difficult to produce and handle via experimental methods.  

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    Modelling coalescence process during breaking of bitumen emulsions
  • 5.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Redelius, Per
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Effects of surfactants and adhesion promoters on the bitumen-minerals interfacial bond during breaking of bitumen emulsionsIn: Article in journal (Refereed)
    Abstract [en]

    Cold mix asphalt (CMA) emulsion technology has been the subject of research for many decades due to its proven environmental and economic benefits. However, issues relating to its mechanical performance still need to be investigated in order to understand the breaking mechanisms of bitumen emulsions and the surface chemistry involved. Bitumen emulsions are designed to break in a controlled manner to achieve the required level of performance for producing good quality cold asphalt mixtures. In this work, experiments on the coalescence of two bitumen droplets were carried out on a selected grade of Nynas bitumen. In an emulsion environment, the cohesion between bitumen droplets as well as their adhesion to a mineral surface was investigated. The cohesion and adhesion properties were analyzed by varying selected surfactant types and adhesion promoters in the water phase. The research showed that the presence of emulsifiers (with concentrations above the critical micelle concentration) in the water phase inhibits the adhesion of bitumen droplets to the mineral surface. However, a very small addition (0.02%) of adhesion promoter reverses the situation completely, and adhesion is dominant rather than cohesion. Moreover, the kinetics of the coalescence process is strongly controlled by the water phase temperature.

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  • 6.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Redelius, Per
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Evaluation of adhesive properties of mineral-bitumen interfaces in cold asphalt mixtures2016In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 125, p. 1005-1021Article in journal (Refereed)
    Abstract [en]

    The performance of asphalt mixtures is strongly influenced by the physical and chemical properties of the minerals and binders used, at various micro to macro scales. In cold asphalt mixtures a process that particularly strongly influences adherence between the minerals and binders (and thus performance) is the wetting of bitumen on the minerals’ surfaces. Their adhesion is influenced by numerous factors and parameters, such as surface free energies of both binders and aggregates in the presence of moisture or dust on the surface of aggregates, mixing temperatures, surface textures including open porosity, nature of the minerals and their surface chemical composition, as well as additives present in the binder phase. However, the relationships involved are not fully understood. Thus, iowever

    n this study the surface free energies of both minerals/aggregates and binders were characterized using two approaches, one based on contact angles and the other on vapor sorption methods. Precise specific surface areas of four aggregates and seven minerals were determined using BET (Brunauer, Emmett and Teller) theory, by measuring the physical adsorption of selected gas vapors on their surfaces, and calculating amounts of adsorbed vapors corresponding to monolayer occupancy on the surfaces. Interfacial bond strengths between bitumen and aggregates were also calculated, based on measured surface free energy components of minerals/aggregates and binders, in both dry and wet conditions. The adhesive bond strength for the binder with each mineral/aggregate combination in wet condition has been improved by using additives. The presented study has highlighted the need for accurate measurements of aggregates’ and minerals’ specific surface areas and (hence) requirements to develop new approaches to resolve problems associated with BET-based methods.

     

  • 7.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Redelius, Per
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Investigating effects of salts on the coalescence process in bitumen emulsionsIn: Article in journal (Refereed)
    Abstract [en]

    The breaking and coalescence process in bitumen emulsions during their application strongly influences the resulting long-term mechanical performance of the cold mix asphalt. This phase separation process is affected by physico-chemical changes at the bitumen/water interface. This paper describes the effects of addition of different salts on the destabilization of bitumen emulsions. This study is limited mainly to cationic rapid setting (CRS) bitumen emulsions and salts which are very commonly added to these emulsions as a stabilizer. However, a few samples with non-ionic emulsifiers were also prepared and analyzed comparatively to understand the electrostatic force balance with varying concentrations of selected salts. The experimental part includes a bitumen droplet relaxation test, droplet size distribution measurement, microscopy, and evaluation of physico-chemical properties of prepared soap solutions e.g. interfacial tension and density measurements. Some experiments on the effect of selected water-soluble organic solvents on the coalescence process were also carried out. The results showed that coalescence was delayed after the addition of salts, while the water soluble organic solvents proved not to affect the emulsion significantly. 

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  • 8.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Redelius, Per
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Surface energy measurements and wettability investigation of different minerals and bitumen for cold asphalts2014In: Asphalt Pavements - Proceedings of the International Conference on Asphalt Pavements, ISAP 2014, CRC Press, 2014, Vol. 1, p. 61-70Conference paper (Refereed)
    Abstract [en]

    For environmental reasons, low installation cost and initial investment; low energy infrastructure materials are becoming of high interest. A potential option to replace current hot mix asphalts is emulsifications, where bitumen binder is dispersed in a water phase aided by emulsifier and shear forces, and mixed at ambient temperature with unheated stones. Long term performance must, however, be guaranteed, otherwise the application benefits will be significantly diminished. In this paper, the main issues of cold mix (emulsion based) asphalt, like wetting in the presence of moisture and dust, and coalescence issues are discussed. Since both bitumen droplets and mineral surfaces were upscaled, pure mineral surfaces were investigated as stone material consists of different minerals. As a measure of the interfacial bond strength, surface free energies of different mineral aggregates and bitumen have been investigated in this paper as a stepping stone for further analyses of emulsions. From the analyses it was found that bitumen has only dispersive forces whereas most of the minerals surfaces have polar nature. According to Fowke's additive nature of the forces, bitumen and water are roughly equally strongly adsorbed to plagioclase and calcite, whereas water will displace bitumen from quartz, gypsum, potassium feldspar and mica surface.

  • 9.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Redelius, Per
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Toward a new experimental method for measuring coalescence in bitumen emulsions: A study of two bitumen droplets2016In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 494, p. 228-240Article in journal (Refereed)
    Abstract [en]

    Cold mix asphalt (CMA) emulsion technology could become an attractive alternative for the road industry due to low startup and equipment installation costs, diminished energy consumption and reduced environmental impact. The performance of cold asphalt mixtures produced from emulsions is strongly influenced by a good control of the breaking and coalescence process. The wetting of bitumen on the surface of the aggregates is hereby of major importance for the performance of the asphalt. Premature coalescence of the bitumen emulsions away from the surface, could lead to poor adhesion and decreased mechanical strength of the asphalt. Today, the breaking and coalescence mechanisms of bitumen emulsions are still not fully understood due to their complexities and the lack of fundamental experimental methods and existing models. However, in the past years efforts have been made in defining relationships for understanding the bitumen emulsions. In this paper, a new experimental method is presented to study coalescence of bitumen by using shape relaxation of bitumen droplets in an emulsion environment. The coalescence of spherical droplets of different bitumen have been correlated with neck growth, densification and surface area change during the coalescence process. The test protocol was designed in a controlled climate chamber, to study the coalescence process with varying environmental conditions. The kinetics of the relaxation process was influenced by the temperature as well as other parameters. The research showed that the developed test procedure is repeatable and able to study the coalescence process on a larger scale. However, the relationship between the measured parametric relationships at the larger scale and the bitumen emulsion scale still needs further investigation.

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  • 10.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Redelius, Per
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Toward understanding breaking and coalescence of bitumen emulsions for cold asphalts2016Conference paper (Other academic)
    Abstract [en]

    Cold mix asphalt (CMA) emulsion based technology is a potential option to replace traditional hot mix asphalt due to environmental benefits and less energy consumption of producing it. However, there are some issues concerned with CMA, for instance, pre-mature coalescence of bitumen emulsions while mixing with minerals or aggregates, which might need more attention to improve the performance of CMA. Actually, the adhesion between the binder and the aggregate surface is largely dependent on the breaking process of bitumen emulsions and the water push-out from the mixtures. This breaking process helps to predict the materials behavior as well as the long term mechanical performance of the mixtures; however, the exact nature of the breaking mechanism of bitumen emulsion is not completely understood until today. The objective of this research is to develop understanding of the structural changes during the phase separation and coagulation stages of the bitumen emulsion. Wettability of bitumen was analyzed by changing the substrate climate conditions. Moreover, this study was extended with the addition of emulsifier and other additives to the binder itself as well as to the water phase. Similar kinds of experiments were setup for exploring the coalescence of bitumen drops in water and emulsifier with other additives.

  • 11.
    Khan, Abdullah
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Saleemi, Mohsin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Johnsson, M.
    Han, L.
    Nong, N. V.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Fabrication, spark plasma consolidation, and thermoelectric evaluation of nanostructured CoSb32014In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 612, p. 293-300Article in journal (Refereed)
    Abstract [en]

    Nanostructured powders of thermoelectric (TE) CoSb3 compounds were synthesized using a chemical alloying method. This method involved co-precipitation of oxalate precursors in aqueous solution with controlled pH, followed by thermochemical treatments including calcination and reduction to produce stoichiometric nanostructured CoSb3. Moreover, CoSb3 nanoparticles were consolidated by spark plasma sintering (SPS) with a very brief processing time. Very high compaction densities (>95%) were achieved and the grain growth was almost negligible during consolidation. An iterative procedure was developed to maintain pre-consolidation particle size and to compensate Sb evaporation during reduction. Significant changes in particle size and morphology were observed, and the post-reduction cooling was found to be an important stage in the process. The spark plasma sintering (SPS) parameters were optimized to minimize the grain growth while achieving sufficient densification. Grain sizes in the range of 500 nm to 1 mu m, with compaction density of 95-98% were obtained. Preliminary measurements of thermal diffusivity and conductivity showed the dependence on grain size as well as on porosity. TE transport properties were measured in the temperature range of 300-650 K. Sample showed p-type behavior with a positive Seebeck coefficient, which increases with increasing temperature. Electrical conductivity measurements indicate metallic behavior and it decreases with increasing temperature. Thermal conductivity also decreases with increasing temperature and major contribution is due to the lattice component. A TE figure of merit of 0.15 was achieved for high purity CoSb3 nanostructured TE material at 650 K and these results are comparable with the values reported for the best unfilled/undoped CoSb3 in the literature.

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