| 1. |
- Paraschos, Georgios Filippos, et al.
(författare)
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Ordered magnetic fields around the 3C 84 central black hole
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- Context . 3C 84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of very-long-baseline interferometry (VLBI) above the hitherto available maximum frequency of 86 GHz. Aims. Using ultrahigh resolution VLBI observations at the currently highest available frequency of 228 GHz, we aim to perform a direct detection of compact structures and understand the physical conditions in the compact region of 3C 84. Methods . We used Event Horizon Telescope (EHT) 228 GHz observations and, given the limited (u, v)-coverage, applied geometric model fitting to the data. Furthermore, we employed quasi-simultaneously observed, ancillary multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. Results . We report the detection of a highly ordered, strong magnetic field around the central, supermassive black hole of 3C 84. The brightness temperature analysis suggests that the system is in equipartition. We also determined a turnover frequency of νm = (113 ± 4) GHz, a corresponding synchrotron self-absorbed magnetic field of BSSA = (2.9 ± 1.6) G, and an equipartition magnetic field of Beq = (5.2 ± 0.6) G. Three components are resolved with the highest fractional polarisation detected for this object (mnet = (17.0 ± 3.9)%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017-2018. We report a steeply negative slope of the spectrum at 228 GHz. We used these findings to test existing models of jet formation, propagation, and Faraday rotation in 3C 84. Conclusions . The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C 84. However, systematic uncertainties due to the limited (u, v)-coverage, however, cannot be ignored. Our upcoming work using new EHT data, which offer full imaging capabilities, will shed more light on the compact region of 3C 84.
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| 2. |
- Tang, Shengwen, et al.
(författare)
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Current and future hydropower development in Southeast Asia countries (Malaysia, Indonesia, Thailand and Myanmar)
- 2019
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Ingår i: Energy Policy. - : Elsevier BV. - 0301-4215. ; 129, s. 239-249
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Tidskriftsartikel (refereegranskat)abstract
- This work discusses the development of hydropower in four Southeast Asia countries. With rapid economic development and insufficient energy supply, hydropower, as an important clean energy, plays a bigger role than before. It is shown that hydropower has immense potential and is the best choice to cater for the energy demand in Southeast Asia. In this work, Malaysia, Indonesia, Thailand and Myanmar are selected to analyze their hydropower development. This work introduces the status of hydropower resources, the current situation of hydropower development and the main distribution of hydropower stations in the four countries. In addition, the paper also introduces some energy policies, the development advantages and obstacles of the four countries, and puts forward suggestions for the future hydropower development of these four countries.
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| 3. |
- Chen, Teresa E, 1988, et al.
(författare)
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Assessment of the mechanical behaviour of reinforcement bars with localised pitting corrosion by Digital Image Correlation
- 2020
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 219
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion of reinforcement in concrete impairs the mechanical behaviour of rebars by decreasing their strength and deformation capacity. In this study, uniaxial tensile tests were carried out on 61 rebars taken from 22 pre- and un- cracked reinforced concrete beams subjected to drying and wetting cycles in chloride solution for over three years. A 3D-scanning technique was used to characterise the maximum local corrosion level, μmax, and different pit shape parameters. Digital Image Correlation (DIC) was used to capture the displacement field of the test bars; the engineering strain was measured through the virtual extensometers created in the DIC post-processing software. The proof and ultimate forces showed linear decreasing trends of μmax, while the proof and ultimate strengths (based on the minimum residual cross-sectional area) were not obviously affected by corrosion. The ultimate strain of corroded bars depended on the gauge length due to strain localisation in the pit. Thus, it was emphasised that the ultimate strain may be overestimated if measured based on a short gauge across the pit. It was also observed that when μmax exceeded a critical local corrosion level (μcrit depending on the ratio between the yield and ultimate strengths of the steel), the region outside the pit did not develop yielding. A lower bound of ultimate strain was further derived as a function of the mechanical parameters of uncorroded steel and maximum local corrosion level. This provided a good comparison with the experimental results. Ultimately, a hypothesis for time-dependent assessment of strain capacity is proposed, considering the evolution of corrosion morphology over time.
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| 4. |
- Chen, Teresa E, 1988, et al.
(författare)
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Comparison of the service life, life-cycle costs and assessment of hybrid and traditional reinforced concrete through a case study of bridge edge beams in Sweden
- 2023
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Ingår i: Structure and Infrastructure Engineering. - : Informa UK Limited. - 1573-2479 .- 1744-8980. ; 19:1, s. 39-57
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Tidskriftsartikel (refereegranskat)abstract
- The edge beams of reinforced concrete bridges with de-icing salts sprayed experience extensive corrosion damage. The average service life of edge beams needing replacement in Sweden has been reported as only 45 years, causing great economic loss to both owners and users. Hence, finding a durable solution for edge beams would benefit society. Hybrid reinforced concrete structures, produced by adding a low-to-moderate fibre content into traditional reinforced concrete, can effectively limit the service crack width and improve resistance to chloride-induced corrosion damage. In this paper, different alternatives of hybrid and traditional reinforced edge beams were designed for a case study. The service life of the alternatives was compared by conducting chloride diffusion calculations and by applying a corrosion-induced cracking model. The economic and environmental (indicated by greenhouse gas emissions) benefits of using hybrid reinforced edge beams were assessed by life-cycle cost analysis and life-cycle assessment. The results showed that the service life of edge beams made of hybrid reinforced concrete can be prolonged by over 58%, thereby enabling a significant reduction in the total life-cycle costs and annual total greenhouse gas emissions.
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| 5. |
- Chen, Teresa E, 1988, et al.
(författare)
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Correlation between concrete cracks and corrosion characteristics of steel reinforcement in pre-cracked plain and fibre-reinforced concrete beams
- 2020
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Ingår i: Materials and Structures/Materiaux et Constructions. - : Springer Science and Business Media LLC. - 1359-5997. ; 53:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results on corrosion characteristics of 66 rebars extracted from un- and pre-cracked plain concrete and fibre-reinforced concrete (FRC) beams suffering from corrosion for more than 3 years. The influences of fibre reinforcement, flexural cracks, corrosion-induced cracks and loading condition on the maximum local corrosion level (defined as the maximum cross-sectional area loss percentage) and pit morphology were examined. With 3D-scanning, the corrosion characteristics were analysed, and pit types were classified based on the maximum local corrosion level and geometric parameters of pits. Corrosion pits were observed near some flexural cracks, while the bars at other cracks were free from corrosion. Most rebars in FRC had less maximum local corrosion level than those in plain concrete under the same loading condition and maximum flexural crack width. However, the maximum local corrosion level was not dependent on the maximum flexural crack width (0.1 and 0.4 mm). Longitudinal cracks (corrosion-induced cracks) aggravated the total steel loss and changed the pit morphology by promoting the pit length development. However, longitudinal cracks did not always form, even with severe pitting corrosion. A hypothesis about the time-dependent interplay between transverse and longitudinal cracks and corrosion development was proposed. Further studies on predicting the pitting corrosion evolution and experimental work on specimens exposed for longer periods are needed to understand and quantify the long-term durability of concrete structures reinforced with both conventional reinforcing bars and fibres.
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| 6. |
- Chen, Teresa E, 1988, et al.
(författare)
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Corrosion Pattern and Mechanical Behaviour of Corroded Rebars in Cracked Plain and Fibre Reinforced Concrete
- 2021
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Ingår i: RILEM Bookseries. - Cham : Springer International Publishing. - 2211-0844 .- 2211-0852. ; 30, s. 477-488
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Konferensbidrag (refereegranskat)abstract
- This paper presents experimental results of corrosion pattern and tensile behaviour of corroded rebars extracted from 4 uncracked and 18 pre-cracked plain concrete and fibre reinforced concrete (FRC) beams. The beams were pre-cracked through three-point bending to a target maximum crack width of 0.1 and 0.4 mm, and then subjected to natural corrosion through cyclic exposure to a 16.5% NaCl solution for more than three years. 3D-scanning was used to characterise the pit morphology and evaluate the maximum local corrosion level of extracted rebars. Under the same loading condition and crack width, most rebars in FRC had smaller maximum local corrosion level than those in plain concrete. Subsequently, tensile tests were carried out on the extracted rebars, with Digital Image Correlation (DIC) technique adopted to investigate the influence of pit morphology on the local strain development. Finally, the time-dependent influence of transverse and longitudinal cracks on the pit morphology which governs the ultimate strain of corroded rebars was discussed. The time-varying nature of corrosion morphology should be considered when predicting the durability and long-term safety of conventional reinforced concrete and FRC structures with reinforcing bars under chloride environments.
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| 7. |
- Chen, Teresa E, 1988, et al.
(författare)
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Hybridarmerade konstruktioner i kloridhaltiga miljöer – beständighet, säkerhet och livscykelkostnader
- 2020
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Ingår i: Bygg och teknik. - 0281-658X. ; 2020:6, s. 14-19
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Livslängden för armerade betongkonstruktioner i kloridhaltiga miljöer kan förlängas genom att kombinera traditionell armering med fibrer i så kallade hybridarmerade lösningar. Detta visades experimentellt i ett tidigare doktorandprojekt i samarbete mellan Chalmers tekniska högskola och Thomas Concrete Group. I ett efterföljande postdocprojekt har vi nu utvecklat modeller som kvantitativt utvärderar fibrernas effekt på beständighet och säkerhet – därigenom visas de positiva resultaten i praktisk användning. Vi har också genomfört en fallstudie som visar de ekonomiska och miljömässiga fördelarna med att använda hybridarmerad betong i kantbalkar.
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| 8. |
- He, Zhen, et al.
(författare)
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The investigation of early hydration and pore structure for limestone powder wastes blended cement pastes
- 2019
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- This work systematically investigates the early hydration process and pore structure evolution of high limestone powder wastes content blended cement pastes by non-contact impedance measurement and microstructural tests. According to the evolution of impedance response, the early hydration process of blende cement pastes can be divided into four stages, denominated as dissolution, acceleration, dynamic balance and hardened stages, respectively. Dynamic balance stage not present in hydration process of pure cement, is a characteristic hydration stage for blended cement pastes. Furthermore, fractal approach for predicting the evolution of pore structure is proposed originally, based on the impedance results.
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| 9. |
- Lundgren, Karin, 1968, et al.
(författare)
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What do we know about concrete, steel, and bond-slip relation for corroded bars?
- 2020
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Ingår i: Capacity Assessment of Corroded Reinforced Concrete Structures. Proceedings of the fib CACRCS DAYS 2020. - 2617-4820. - 9782940643103
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Konferensbidrag (refereegranskat)abstract
- Reinforcement corrosion influences the deformation and load capacity of steel rebars. Further, it generates splitting stresses that weaken the concrete and strongly affect the bond between reinforcement and concrete. Here, a recently published engineering model to determine the deformation capacity of rebars with pitting corrosion is described. Further, the effect of corrosion on bond is described in a systematic way, with an overview of the effect for various cases depending on reinforcement type, existence of transverse reinforcement, and confinement due to concrete and boundaries. Finally, an engineering model to determine bond-slip relationships for ribbed bars is presented.
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| 10. |
- Lundgren, Karin, 1968, et al.
(författare)
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What do we know about concrete, steel, and bond-slip relation for corroded bars? (key-note lecture)
- 2021
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Ingår i: fib Symposium. - 2617-4820. ; , s. 123-130
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Konferensbidrag (refereegranskat)abstract
- Reinforcement corrosion influences the deformation and load capacity of steel rebars. Further, it generates splitting stresses that weaken the concrete and strongly affect the bond between reinforcement and concrete. Here, a recently published engineering model to determine the deformation capacity of rebars with pitting corrosion is described. Further, the effect of corrosion on bond is described in a systematic way, with an overview of the effect for various cases depending on reinforcement type, existence of transverse reinforcement, and confinement due to concrete and boundaries. Finally, an engineering model to determine bond-slip relationships for ribbed bars is presented.
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