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  • 1.
    Hailesilassie, Biruk
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Morphology Characterization of Foam Bitumen and Modeling for Low Temperature Asphalt Concrete2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Development of new asphalt technologies to reduce both energy consumption and CO2 production has attracted great interest in recent years. The use of foam bitumen, as one of them, is attractive due to the low investment and production cost. Formation and decay of foam bitumen is a highly dynamic temperature dependent process which makes characterization difficult. In this thesis, new experimental tools were developed and applied for characterizing the foam bitumen during the hot foaming process. 

    One of the main goals of this study was to improve understanding and characterization of the foam bitumen formation and decay. X-ray radiography was used to study the formation and decay of foam bitumen in 2D representation. The results demonstrate that the morphology of bubble formation depends on the types of bitumen used. Moreover, theoretical investigation based on the 3D X-ray computed tomography scan dataset of bubble merging showed that the disjoining pressure increased as the gap between the bubbles in the surface layer (foam film) decreased with time and finally was ruptured. 

     Examining the foam bitumen stream right at the nozzle revealed that foam bitumen at a very early stage contains fragmented pieces of irregular size rather resembling a liquid than foam. The result from thermogravimetric analysis demonstrated that residual water content depends on the initial water content, and was found to be between 38 wt% and 48 wt% of the initial water content of 4 wt% to 6 wt%.

    Moreover the influence of viscosity and surface tension on bubble shape and rise velocity of the bubbles using level-set method was implemented in finite element method. The modeling results were compared with bubble shape correlation map from literature. The results indicated that the bubble shapes are more dependent on the surface tension parameters than to the viscosity of the bitumen, whereas the bitumen viscosity is dominant for bubble rising velocity.

  • 2.
    Hailesilassie, Biruk
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Jerjen, Iwan
    Griffa, Michele
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swiss Federal Laboratories for Material Science and Technology, Duebendorf, Switzerland .
    A Closer Scientific Look at Foam BitumenManuscript (preprint) (Other academic)
  • 3.
    Hailesilassie, Biruk
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swiss Federal Laboratories for Material Science and Technology, Duebendorf, Switzerland .
    Modeling of bubble rising velocity and shape for foam bitumenManuscript (preprint) (Other academic)
  • 4.
    Hailesilassie, Biruk W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Hean, Sivotha
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swiss Federal Laboratories for Material Science and Technology (EMPA), Switzerland.
    Testing of blister propagation and peeling of orthotropic bituminous waterproofing membranes2015In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 48, no 4, p. 1095-1108Article in journal (Refereed)
    Abstract [en]

    Bridge decks are commonly subjected to harsh environmental conditions that often lead to serious corrosion problems, which are triggered by blisters under the hot mix asphalt bridge deck pavement with waterproofing membranes. These blisters are secretly evolving during weather exposure until often being detected too late. Formation of blisters under the waterproofing membrane is caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. This paper primarily intends to adopt the analytical blister propagation energy approach for waterproofing membranes and compare it with adhesive fracture energy from standard peeling test methods, already described in the literature. Three different types of polymer modified bitumen membranes (PBM) were used for this purpose. The investigation includes a comparison between uniaxial and biaxial testing conditions for determining the modulus of elasticity of the membranes. Moreover, the influence of the displacement rate and temperature on the adhesive fracture energy in peeling tests is investigated. It was found that the biaxial modulus of PBM in the longitudinal and transversal direction is comparable with the uniaxial tension testing results in the main directions. In addition, it was observed that the ratio of longitudinal and transversal modulus of elasticity was similar. The energy calculated from tests with elliptical blister propagation showed a comparable value to the standard peeling fracture energy for similar types of PBM.

  • 5.
    Hailesilassie, Biruk W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Hugener, Martin
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials.
    Influence of foaming water content on foam asphalt mixtures2015In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 85, p. 65-77Article in journal (Refereed)
    Abstract [en]

    Warm mix asphalt technology using foamed bitumen is being used widely despite the fact that high air void content and poor coating of large aggregate remain major drawbacks require enhancement. This paper manly focuses on the investigation of water content influence on the foamed bitumen and the asphalt mixture. Influence of the water content in combination with compaction temperature has been investigated using gyratory compaction method. AC11N foam asphalt mixture is produced in the lab using lab foamer. Marshall stability and indirect tensile test was used to evaluate the foam asphalt mixture performance. The investigation revealed that the Marshall stability of foam asphalt mixture is highly influenced by compaction temperature compared to water content. Moreover, increasing the water content helps in coating large aggregates when the mixture is produced at low temperature, nevertheless using high water content reduces the Marshall stability to certain extent. In addition the amount of water trapped in the mixture after the mixing process was determined using thermogravimetric analysis. The amount of water remaining in the asphalt mixture is less than 1% relative to the bitumen mass.

  • 6.
    Hailesilassie, Biruk W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Schuetz, Philipp
    Jerjen, Iwan
    Bieder, Andrea
    Hugener, Martin
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swiss Federal Laboratories for Material Science and Technology, Duebendorf, Switzerland .
    Evolution of bubble size distribution during foam bitumen formation and decay2014In: Asphalt Pavements: Proceedings of the International Conference on Asphalt Pavements, ISAP 2014 / [ed] Kim, YR, BOCA RATON: CRC PRESS-TAYLOR & FRANCIS GROUP , 2014, p. 1233-1240Conference paper (Refereed)
    Abstract [en]

    The warm asphalt mixture process using foam asphalt technology allows mixing and compaction at lower temperature. Nevertheless the higher air void content and incomplete coating of large aggregates are issues that need improvement to reach the properties of hot mix asphalt. In order to improve the understanding and characterization of the bitumen foam, X-ray radiography was used to investigate the formation and decay of bitumen foam in 2D representation. Image segmentation analysis was used to determine the foam bubble size distribution as a function of time. The impact of water content on the process has been studied for two penetration grade bitumen. The water content showed considerable influence on the foam quality in terms of expansion ratio and bubble size distribution. Increasing the water content in the foaming process leads to a quicker collapse of the bubbles and favors coalescence of individual bubbles.

  • 7.
    Hailesilassie, Biruk W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Schuetz, Philipp
    Jerjen, Iwan
    Hugener, Martin
    Partl, Manfred N.
    Dynamic X-ray radiography for the determination of foamed bitumen bubble area distribution2015In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 50, no 1, p. 79-92Article in journal (Refereed)
    Abstract [en]

    Foam bitumen is highly efficient in wetting and coating the surface of mineral aggregate at lower temperature. In order to improve understanding and characterization of the bitumen foam, X-ray radiography was used to study the formation and decay of bitumen foam in 2D representation. Image segmentation analysis was used to determine the foam bubble size distribution. In addition, the main parameters influencing foam bitumen formation, water content, and temperature were also investigated. The results demonstrate the influence of the water content on morphology and expansion of foam bitumen bubbles. Adding more water in the foaming process leads to quick collapse of bubbles and intensifies coalescence of foam bitumen. Higher temperatures produces larger bubbles at early foaming stage compared to lower temperature. Moreover the morphology of bubble formation depends on the types of bitumen used. An exponential function has been implemented to represent the bubble area distribution.

  • 8.
    Hailesilassie, Biruk Wobeshet
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mechanisms of Blister Formation on Concrete Bridge Decks with Waterprooving Asphalt Pavement Systems2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Bridge decks are commonly subjected to harsh environmental conditions that often lead to serious corrosion problems triggered by blisters under the hot mix asphalt bridge deck surfacing and secretly evolving during weather exposure until damage is often detected too late. Blisters may form under both the waterproofing dense mastic asphalt layer or under the waterproofing membrane which is often applied as additional water protection under the mastic asphalt (MA). One of the main technical issues is the formation of blisters under the membrane and asphalt-covered concrete structures caused by a complex mechanism governed by bottom-up pressure and loss of adhesion.

    A linear viscoelastic finite-element model was developed to simulate time-dependent blister growth in a dense mastic asphalt layer under uniformly applied pressure with and without temperature and pressure fluctuation. A finite element model was developed using ABAQUS with linear viscoelastic properties and validated with a closed form solution from first-order shear-deformation theory for thick plates. In addition, the blister test was conducted on different samples of MA in the laboratory and digital image correlation measurement technique was used to capture the three-dimensional vertical deflection of the MA over time. It was found that the blister may grow continuously under repeated loading conditions over subsequent days.

    With respect to blistering under waterproofing membranes, mechanical elastic modeling and experimental investigations were performed for three different types of membranes under in-plane stress state. The orthotropic mechanical behavior of a polymer modified bitumen membrane (PBM) was determined from biaxial test data. Finally, blister tests by applying controlled pressure between orthotropic PBMs and concrete plates were performed for studying the elliptical adhesive blister propagation using digital 3D image correlation. The energy calculated from elliptical blister propagation was found comparable to the adhesive fracture energy from standard peeling tests for similar types of PBMs. This indicates that the peeling test assists to evaluate and rank the adhesive properties of different types of membranes with respect to blister formation at room temperature without conducting time consuming and complicated pressurized blister propagation tests using digital 3D image correlation.

  • 9.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Hean, Sivotha
    Swiss Federal Laboratories for Material Science and Technology.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Comparison between Blister Propagation and Peeling Test for an Orthotropic Bituminous Waterproofing MembraneArticle in journal (Other academic)
    Abstract [en]

    Bridge decks are commonly subjected to harsh environmental conditions that often lead to serious corrosion problems, which are triggered by blisters under the hot mix asphalt bridge deck pavement with waterproofing membranes. These blisters are secretly evolving during weather exposure until often being detected too late. Formation of blisters under the waterproofing membrane is caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. This paper intends to adopt the analytical blister propagation energy approach for waterproofing membranes and compare it with adhesive fracture energy from standard peeling test methods, already described in the literature. Three different types of polymer modified bitumen membranes (PBMs) were used for this purpose. The investigation includes a comparison between uniaxial and biaxial testing conditions for determining the modulus of elasticity of the membranes. Moreover, the influence of the displacement rate and temperature on the adhesive fracture energy in peeling tests is investigated. It was found that the biaxial modulus of PBM in the longitudinal and transversal direction is comparable with the uniaxial tension testing results in the main directions. In addition, it was observed that the ratio of longitudinal and transversal modulus of elasticity was similar. The energy calculated from tests with elliptical blister propagation showed a comparable value to the standard peeling fracture energy for similar types of PBMs. This indicates that the peeling test assists in ranking the adhesive properties of different types of membranes. It also allows ranking between the membranes with respect to resistance to blister formation without time consuming and complicated pressurized blister propagation tests and digital image correlation techniques.

  • 10.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Hugener, M.
    Bieder, A.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. EMPA, Swiss Federal Laboratories for Material Science and Technology, Switzerland.
    New experimental methods for characterizing formation and decay of foam bitumen2015In: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873Article in journal (Refereed)
    Abstract [en]

    Formation and decay of foam bitumen is a highly dynamic temperature dependent process which makes characterization difficult. In this research, new experimental tools were applied for characterizing the bitumen foam during the foaming process. Ultrasonic sensors were used for accurately monitoring the expansion and decay of foam bitumen as a function of time. Assessment of foam bitumen viscosity was performed using high frequency torsional rheometer and in situ observation by X-ray radiography. A high-speed camera was applied for examining the foam bitumen stream right at the nozzle revealing that foam bitumen at a very early stage contains fragmented pieces of irregular size rather resembling a liquid than foam. Moreover, infrared thermal images were taken for obtaining information on the in situ surface temperature of foam bitumen during the hot foaming process. The result showed that the average surface temperature of foam bitumen depends on the water content of the bitumen and bubble size distribution, 108 and 126 °C for 4 and 1 wt% (by weight) water content respectively. The residual water content in the decaying foam bitumen was determined by thermogravimetric analysis. The result demonstrated that residual water content depends on the initial water content, and was found to be between 38 and 48 wt% of the initial water content of 4–6 wt%. Finally, X-ray computed tomography was applied for examining the decay of foam bitumen revealing that the bubbles of foam bitumen remain trapped close to the surface of the foam bitumen.

  • 11.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science.
    Jerjen, I.
    Griffa, M.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Materials. Swiss Federal Laboratories for Material Science and Technology, Duebendorf, Switzerland .
    A closer scientific look at foam bitumen2017In: Road Materials and Pavement Design, ISSN 1468-0629, Vol. 18, no 2, p. 362-375Article in journal (Refereed)
    Abstract [en]

    In the asphalt industry, a substantial interest is observed to find possibilities to reduce the production temperature of asphalt mixtures. In the context of this research, new methods for the visualisation of unstable bitumen foam, such as dynamic X-ray radiography, computed tomography (CT) and high-speed camera investigations, have been developed. Moreover, characterisation with empirical methods such as expansion ratio and half-life was determined accurately using ultrasonic measurements. This opens new possibilities to characterise bitumen foam (foaming process) for practical applications. Examination of the foam bitumen stream using a high-speed camera revealed that the foam bitumen contains fragmented pieces of bitumen, which resemble more a liquid than foam. This indicates that the foam is formed afterwards and not, as assumed, within the expansion chamber of the foam generator. In situ thermal imagery of the surface, during the hot foaming process, showed that the temperature distribution depends on the foaming water content (W.C.) and bubble size distribution. Higher W.C. results in more inhomogeneous temperature distribution as compared to lower W.C. (<2 wt%). The dynamic X-radiography results indicated that as the foam decays, the bubble size distribution becomes progressively larger with time for 160°C bitumen temperature. Furthermore, at the beginning of the foam formation, majority of the bubbles is small in cross-section size (0.2–10 mm2). At a later stage, the bubbles become polydisperse. Moreover, theoretical investigations based on the 3D X-ray CT scan data set of bubble merging show that the disjoining pressure increases as the foam film gets thinner with time and finally undergoes rupture. The speed of the bubbles also increases with time when the bubbles are getting closer to each other.

  • 12.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Adhesive Blister Propagation under an Orthotropic Bituminous Waterproofing Membrane2013In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 48, p. 1171-1178Article in journal (Refereed)
    Abstract [en]

    In most countries, waterproofing systems used on concrete bridge decks or roofs of buildings are generally based on orthotropic bituminous membranes; amongst these, styrene-butadiene-styrene copolymer (SBS) and atactic polypropylene (APP) polymer modified bituminous membranes are being used in most applications. One of the main technical concerns is the formation of blisters under the membrane caused by a complex mechanism governed by bottom-up pressure and loss of adhesion. This paper intends to contribute in understanding this mechanism by mechanical elastic modeling and experimental investigation. In order to study the material properties of SBS membranes under the in-plane complex stress state, the orthotropic mechanical behavior of a polymer modified bitumen membrane (PBM) was determined from biaxial test data. Hence, the measured stress-strain data were analyzed using the orthotropic equation to find the material properties in the longitudinal and transversal direction. Finally, blister tests were performed on concrete plates for studying adhesive blister propagation by applying controlled pressure between the PBM and the concrete plates. It was found that the ratio of the longitudinal to transversal adhesive blister propagation is comparable to the ratio of the modulus of elasticity in the longitudinal to transversal direction. Due to the orthotropic material property of the PBM, elliptical adhesive blister propagation was observed and a new model proposed for determining the energy for elliptical adhesive blister propagation.

  • 13.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mechanisms of asphalt blistering on concrete bridges2012In: Journal of ASTM International, ISSN 1546-962X, E-ISSN 1546-962X, Vol. 9, no 3Article in journal (Refereed)
    Abstract [en]

    Blistering is a major problem in asphalt-covered concrete structures, such as multi-storage parking buildings, built-up roofs, tunnels, pedestrian areas, or concrete bridge decks. In this particular research, a linear viscoelastic finite-element model is developed to simulate time-dependent blister growth in an asphalt layer under uniformly applied pressure with and without temperature and pressure fluctuation. Indirect tensile tests on mastic asphalt (MA) are performed at three different temperatures to characterize and determine the material properties for the model. A three-dimensional thick-plate axisymmetric finiteelement model is developed using ABAQUS with linear viscoelastic properties and validated with closedform solution from first-order shear-deformation theory for thick plates. Elastic-viscoelastic analogy is used to find an analytic solution for the time-dependent deflection of the blister. In addition, the blister test is conducted on different samples of MA in the laboratory and digital image correlation measurement technique is used to capture the three-dimensional vertical deflection of the MA with time. Finally, the results from image correlation are compared with the finite-element simulation and thick-plate theory analytic solution. The finite-element model simulation shows that the daily temperature variations may have a significant influence on blister growth in asphalt pavements. It is found that the blister can grow continuously under repeated loading conditions over subsequent days. The study concludes that temperature fluctuation in the blister has more influence on blister growth than fluctuation of the pressure inside the blister.

  • 14.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Partl, Manfred
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mechanisms of Short-term Blistering Affecting Deterioration of Concrete Structures with Asphalt Pavements2011Conference paper (Other academic)
  • 15.
    Hailesilassie, Biruk Wobeshet
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Partl, Manfred N.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mechanisms of asphalt blistering on concrete bridges2012In: Durability of building and construction sealants and adhesives: 4th volume, ASTM International, 2012, p. 308-330Conference paper (Refereed)
    Abstract [en]

    Blistering is a major problem in asphalt-covered concrete structures, such as multi-storage parking buildings, built-up roofs, tunnels, pedestrian areas, or concrete bridge decks. In this particular research, a linear viscoelastic finite-element model is developed to simulate time-dependent blister growth in an asphalt layer under uniformly applied pressure with and without temperature and pressure fluctuation. Indirect tensile tests on mastic asphalt (MA) are performed at three different temperatures to characterize and determine the material properties for the model. A three-dimensional thick-plate axisymmetric finite-element model is developed using ABAQUS with linear viscoelastic properties and validated with closed-form solution from first-order shear-deformation theory for thick plates. Elastic-viscoelastic analogy is used to find an analytic solution for the time-dependent deflection of the blister. In addition, the blister test is conducted on different samples of MA in the laboratory and digital correlation measurement technique is used to capture the three-dimensional vertical deflection of the MA with time. Finally, the results from image correlation are compared with the finite-element simulation and thick-plate theory analytic solution. The finite-element model simulation shows that the daily temperature variations may have a significant influence on blister growth in asphalt pavements. It is found that the blister can grow continuously under repeated loading conditions over subsequent days. The study concludes that temperature fluctuation in the blister has more influence on blister growth than fluctuation of the pressure inside the blister.

1 - 15 of 15
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