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| 2. |
- Bernstone, Christian, et al.
(författare)
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Verifiering av struktur och fuktmekaniska beräkningsverktyg : Tillämpning på reaktorinneslutningars betongkonstruktioner, Vercors Fas 1
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Électricité de France har utanför Paris byggt en 1/3 skalmodell av en reaktorinneslutning motsvarande en fransk fullskalereaktor modell P4. Anläggningen möjliggör studier av hur åldringsprocesser påverkar förspända reaktorinneslutningar. Syftet är att efter de 7 år som ett övergripande forskningsprojektet vid på anläggningen pågår, uppnå påverkan motsvarande den åldring som en fullskalereaktor har utsatts för efter 6o års drift.Konstruktionen har försetts med ett omfattande instrumenteringsprogram som gör det möjligt att följa konstruktionens beteende i tidigt skede och över tid. Ett av anläggningens forskningsprojekt omfattar en benchmark av olika beräkningsverktygs möjlighet att kunna förutse konstruktionens beteende i tidigt skede och under själva åldrandet, dess täthet till följd av åldrandet och beteende under svåra haveriförhållanden. Denna benchmark har genomförts via en öppen inbjudning till intresserade experter att delta. I projektet, benämnt VeRCoRs , bidrar deltagande organisationer med egna modelleringsarbeten utifrån de tre olika teman. Arbetet med det första temat startade 2015 (tidigt skede), därefter följer den åldrade konstruktionen (2017) och svåra haverisituationer (2021). Denna rapport redovisar det arbete som har gjorts för det första temat (Tema 1) inom ramen för ett Energiforskuppdrag.Modelleringsarbetet har till största delen genomförts av LTH i nära samarbete med KTH och Vattenfall. Simuleringar har gjorts för den unga betongens beteende under den ett år långa byggfasen, med hänsyn tagen till betongens hydratation (temperaturberäkningar/värmeutveckling), uttorkning (självuttorkning och fukttransport) och deformationer (temperatur-, fukt-, kryp-, och spänningsrelaterade deformationer). Resultatet har jämförts mot data från anläggningens instrumentering. Dessutom så har en genomgång gjorts av resultaten från övriga deltagares arbeten i Tema 1.Sammanfattningsvis så visar resultaten på de fördelar som finns med att genom avancerade beräkningar verifiera designparametrar och prognostisering av reaktorinneslutningars funktion, men också på utmaningar. Med hjälp av FEmodellering så kan det tidiga skedet efter färdigställd konstruktion beskrivas både vad gäller temperatur- och deformationer med rimlig tillförlitlighet. Det finns dock potential till förbättringar. Även om betongens temperatur kan predikteras noggrant så kan det skilja kraftigt i uppskattningen av inducerade påkänningar. En viktig orsak till dessa skillnader beror på osäkerheter i bestämning av krypning och krympning i betongen tidiga skede.
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| 3. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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A hygro-thermo-mechanical multiphase model for long-term water absorption into air-entrained concrete
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water in the concrete, and it might take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of water filling of air pores is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the Thermodynamically Constrained Averaging Theory (TCAT) as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete, and yield results that comply with laboratory and in situ measurements.
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| 4. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete
- 2019
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Ingår i: Transport in Porous Media. - Netherlands : Springer. - 0169-3913 .- 1573-1634. ; 127:1, s. 113-141
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Tidskriftsartikel (refereegranskat)abstract
- Many concrete structures located in cold climates and in contact with free water are cast with air-entrained concrete. The presence of air pores significantly affects the absorption of water into the concrete, and it may take decades before these are fully saturated. This generally improves the long-term performance of such structures and in particular their frost resistance. To study the long-term moisture conditions in air-entrained concrete, a hygro-thermo-mechanical multiphase model is presented, where the rate of filling of air pores with water is described as a separate diffusion process. The driving potential is the concentration of dissolved air, obtained using an averaging procedure with the air pore size distribution as the weighting function. The model is derived using the thermodynamically constrained averaging theory as a starting point. Two examples are presented to demonstrate the capabilities and performance of the proposed model. These show that the model is capable of describing the complete absorption process of water in air-entrained concrete and yields results that comply with laboratory and in situ measurements.
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| 5. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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Comparison of mechanistic and phenomenological approaches to model drying shrinkage of concrete
- 2017
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Ingår i: Nordic Concrete Research. ; , s. 287-290
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Konferensbidrag (refereegranskat)abstract
- Drying shrinkage of concrete is often estimated using a phenomenological approach where it is assumed that shrinkage is proportional to the change in internal humidity. In this study, a mechanistic approach was used which instead aims to mathematically describe the physical processes of drying shrinkage. Simulations of two laboratory tests were made and compared to results from two models based on the phenomenological approach. The results show that the developed model can describe drying shrinkage of concrete equally well as the phenomenological models but without the need to specify the final drying shrinkage strain.
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| 6. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damages are frequently detected during inspections. However, it is often hard to assess the extent and severity of these damages and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. The results show that the model can reproduce the freezing behaviour observed in the experimental tests on a structural scale as well as being capable of describing freezing induced deformations caused by non-uniform moisture distributions.
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| 7. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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Freezing of partially saturated air-entrained concrete: A multiphase description of the hygro-thermo-mechanical behaviour
- 2018
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 152-153, s. 294-304
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Tidskriftsartikel (refereegranskat)abstract
- Even though air-entrained concrete is usually used for concrete structures located in cold climates that are exposed to wet environments, frost damage is frequently detected during inspections. However, it is often hard to assess the extent and severity of the damage and, thus, there is a need for better tools and aids that can complement already established assessment methods. Several studies have successfully shown that models based on poromechanics and a multiphase approach can be used to describe the freezing behaviour of air-entrained concrete. However, these models are often limited to the scale of the air pore system and, hence, hard to use in applications involving real structures. This study proposes a hygro-thermo-mechanical multiphase model which describes the freezing behaviour of partially saturated air-entrained concrete on the structural scale. The model is implemented in a general FE-code and two numerical examples are presented to validate and show the capabilities of the model. The first concerns a series of experimental tests of air-entrained cement pastes, whereas the second aims to show the capability of the model to account for an initial non-uniform distribution of moisture. While the model predictions underestimate the magnitude of the measured strains, the results still show that the model can capture the general freezing behaviour observed in the experimental tests on the structural scale. Furthermore, the results demonstrate that the model is capable of describing freezing induced deformations caused by non-uniform moisture distributions.
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| 8. |
- Eriksson, Daniel, 1987-, et al.
(författare)
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Influence of air voids in multiphase modelling for service life prediction of partially saturated concrete
- 2018
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Ingår i: Computational Modelling of Concrete Structures. - London, UK : CRC Press. - 9781138741171 - 9781315182964 ; , s. 317-326
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Konferensbidrag (refereegranskat)abstract
- The purpose of this study is to show the influence and significance of including water filling of air pores when studying moisture conditions in concrete structures cast with air-entrained concrete and in contact with free water. Especially if the aim is to assess the risk for frost damages in different regions of the structure, based on a critical degree of saturation, in order to ultimately perform a service life prediction. A hygro-thermo-mechanical multiphase model that includes the effect of water filling in air pores, recently presented by the authors, is briefly described and applied in two numerical examples. The results show moisture distributions that would not be possible to capture without the air pore filling included in the model. More importantly, the general shape of these distributions complies well with measured distributions in real concrete structures as well as with distributions obtained in laboratory measurements.
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| 9. |
- Gasch, Tobias, et al.
(författare)
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A coupled hygro-thermo-mechanical model for concrete subjected to variable environmental conditions
- 2016
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 91, s. 143-156
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Tidskriftsartikel (refereegranskat)abstract
- It is necessary to consider coupled analysis methods for a simulation to accurately predict the long-term deformations of concrete structures. Among other physical fields that can be considered, both temperature and moisture have a significant influence on the deformations. Variations of these fields must therefore be included implicitly in an analysis. This paper presents a coupled hygro-thermo-mechanical model for hardened concrete based on the framework of the Microprestress-Solidification theory. The model accounts for important features of concrete such as ageing, creep, shrinkage, thermal dilation and cracking; all of these under variable temperatures and moisture conditions. It is discussed how to implement the proposed model in a flexible numerical framework that is especially suitable for multi-physics analyses. The capabilities of the model are shown through the analysis of three experimental data sets from the literature, with focus on creep and shrinkage. Overall, the agreement between the analysis and experimental results is good. Finally, a numerical example of a concrete gravity dam with dimensions and loads typical to northern Sweden is analysed to show the capabilities of the model on a structural scale.
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| 10. |
- Gasch, Tobias, et al.
(författare)
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A coupled multi-physics model for creep, shrinkage and fracture of early-age concrete
- 2016
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Ingår i: 9th International Conference on Fracture Mechanics of Concrete and Concrete Structures.
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Konferensbidrag (refereegranskat)abstract
- The behaviour of concrete at early-age is complex and involves several physical fieldssuch as temperature, moisture and deformations. In this paper a hygro-thermo-chemo-mechanicalmodel for the analysis of early-age concrete based on a combination of models from the literature ispresented. The chemical model is based on the reaction degree concept, also used to define internal actions such as self-desiccation and ageing of mechanical properties. A mechanical model based on the Microprestress-Solidification theory for concrete creep is used, that in a simplified manner alsoconsiders concrete fracture. The model has been implemented in a numerical framework suitable for coupled multi-physics problems. It is here applied to a case study of an un-reinforced concrete tunnel plug made of a low-pH self-compacting concrete. Good agreement is generally obtained with measurements and hypotheses previously made on the behaviour of the plug are verified.
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