| 1. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Physical and Mechanical Properties of Cementitious Specimens Exposed to an Electrochemically Derived Accelerated Leaching of Calcium
- 2015
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Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 1976-0485 .- 2234-1315. ; 9:3, s. 295-306
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Tidskriftsartikel (refereegranskat)abstract
- Simulating natural leaching process for cementitious materials is essential to perform long-term safety assessments of repositories for nuclear waste. However, the current test methods in literature are time consuming, limited to crushed material and often produce small size samples which are not suitable for further testing. This paper presents the results from the study of the physical (gas permeability as well as chloride diffusion coefficient) and mechanical properties (tensile and compressive strength and elastic modulus) of solid cementitious specimens which have been depleted in calcium by the use of a newly developed method for accelerated calcium leaching of solid specimens of flexible size. The results show that up to 4 times increase in capillary water absorption, 10 times higher gas permeability and at least 3 times higher chloride diffusion rate, is expected due to complete leaching of the Portlandite. This coincides with a 70 % decrease in mechanical strength and more than 40 % decrease in elastic modulus.
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| 2. |
- Fernandez, Ignasi, 1984, et al.
(författare)
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Mechanical Properties of 30 Year-Old Naturally Corroded Steel Reinforcing Bars
- 2019
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Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 2234-1315 .- 1976-0485. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- The present paper investigates the mechanical response of more than 120 corroded reinforcing bars extracted from a real bridge after 30 years in service. Corrosion was quantified using gravimetric and 3D-laser scanning measurements. An expression to relate the average and critical corrosion levels was found, the latter being the main parameter governing the capacity of corroded bars. Whereas the strength of the material was not affected by corrosion, the ultimate strain decreased sharply. However, strains were not only affected by cross-sectional reduction but also by the shape of the critical pit and necking at failure.
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| 3. |
- Fernandez, Ignasi, 1984, et al.
(författare)
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Ultimate Capacity of Corroded Statically Indeterminate Reinforced Concrete Members
- 2018
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Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 2234-1315 .- 1976-0485. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The corrosion of steel reinforcement is commonly believed to be the primary cause of structural deterioration of reinforced concrete (RC) structures; as a result of this deterioration, a RC structure can incur a considerable reduction in structural serviceability and safety. Because of their inherent redundancy, statically indeterminate structures develop resistant mechanisms that can potentially assist in delaying the collapse of severely damaged RC structures. In order to experimentally demonstrate these resistant mechanisms, four groups of three two-span continuous RC beam members each were deteriorated using induced corrosion methods and tested to failure under monotonic loads. For control, one group of three RC beams was left uncorroded and similarly load tested. All the RC beam specimens subjected to corrosion demonstrated a significant reduction (a maximum reduction of 55% as compared to the uncorroded control group) of their ultimate capacity. The presence of corrosion induced a transition from flexural failure to anchorage failure in some specimens; despite the induced damage some redistributed structural capacity was observed. Modelling of deterioration effects by the inclusion of different aspects of corrosion was also conducted. Three-dimensional (3D) Finite-Element Method (FEM) models were developed to assess the variation in the mechanical properties of the corroded steel and the reduction in the bond interaction between concrete and steel due to the corrosion of the steel reinforcement. In general, the current 3D FEM models demonstrated a good agreement with the experimental data; however, 3D FEM models that exhibit greater sophistication are necessary to better describe the failure mode of some RC beam specimens when they are associated with local effects.
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| 4. |
- Flansbjer, Mathias, et al.
(författare)
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Composite Behaviour of Textile Reinforced Reactive Powder Concrete Sandwich Façade Elements
- 2018
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Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 1976-0485 .- 2234-1315. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Within the EC funded project smart elements for sustainable building envelopes, carbon textile reinforcement was incorporated into reactive powder concrete, namely textile reinforced reactive powder concrete (TRRPC), to additionally improve the post-cracking behaviour of the cementitious matrix. This high-performance composite material was included as outer and inner façade panels in prefabricated and non-load bearing sandwich elements along with low density foamed concrete (FC) and glass fibre reinforced polymer continuous connecting devices. Experiments and finite element analysis (FEA) were applied to characterize the structural performance of the developed sandwich elements. The mechanical behaviour of the individual materials, components and large-scale elements were quantified. Four-point bending tests were performed on large-scale TRRPC-FC sandwich element beams to quantify the flexural capacity, level of composite action, resulting deformation, crack propagation and failure mechanisms. Optical measurements based on digital image correlation were taken simultaneously to enable a detailed analysis of the underlying composite action. The structural behaviour of the developed elements was found to be highly dependent on the stiffness and strength of the connectors to ensure composite action between the two TRRPC panels. As for the FEA, the applied modelling approach was found to accurately describe the stiffness of the sandwich elements at lower load levels, while describing the stiffness in a conservative manner after the occurrence of connector failure mechanisms. © 2018, The Author(s).
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| 5. |
- Lundgren, Karin, 1968, et al.
(författare)
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Methodology for Testing Rebar-Concrete Bond in Specimens from Decommissioned Structures
- 2019
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Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 2234-1315 .- 1976-0485. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Mimicking natural deterioration in accelerated tests is challenging; a highly relevant alternative option is to use deteriorated specimens from decommissioned structures. This paper describes a methodology to select and design tests of the bond and anchorage between reinforcement and concrete in such specimens, with the aim of providing general information, needed when developing methods for assessing structures in general. The methodology includes the following steps: (1) choice of existing structure for samples, (2) choice of test method, (3) design of test setup, and (4) design of test programme. Each step is discussed in detail and comments are made on considerations and challenges arising specifically due to the use of specimens from existing structures. As the scatter of test results is typically large, a suitable test method should enable a large number of tests by being robust, quick and affordable. It is recommended to keep track of the position of the specimens in the original structure, to document cracks, and to take samples also of uncorroded bars. These can then be used for reference in quantifying the corrosion level of corroded bars. This methodology is exemplified in the design of three test series on edge beams from two bridges; two series resulted in beam test setups and one in direct pull-out tests. The methodology described strongly highlights that careful investigations are required to design experiments which generate reliable data. Acquiring data from decommissioned structures will improve our understanding of the structural behaviour of existing structures and thus enable improved assessment methods.
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| 6. |
- Ylmén, Rikard, 1982, et al.
(författare)
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Carbonation of Portland Cement Studied by Diffuse Reflection Fourier Transform Infrared Spectroscopy
- 2013
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Ingår i: International Journal of Concrete Structures and Materials. - : Springer Science and Business Media LLC. - 2234-1315 .- 1976-0485. ; 7:2, s. 119-125
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Tidskriftsartikel (refereegranskat)abstract
- Carbonation is a natural ageing process for cement. This study focuses on how the carbonation rate varies with selected hydration times and atmospheric conditions during the early stages of reacting dried cement paste. Diffuse reflection Fourier transform infrared spectroscopy is shown to be a suitable technique to monitor the formation of carbonates in cement. Combined with a previously developed freeze drying technique, carbonation can be studied at specific hydration stages. In ambient air both calcium hydroxide and calcium silicate hydrate (C–S–H) in cement are carbonated. Increased hydration time enhances the carbon dioxide uptake, which indicates that the calcium in the hydration products reacts more easily than the calcium in the clinker phase. In a humid CO2 atmosphere, the carbonation process is so pronounced that it decomposes C–S–H into calcium carbonate and silica. In a moist N2 atmosphere no carbonation occurs, but the sulfate chemistry of the cement seems to be affected due to the formation of ettringite.
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