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Multiphysical analysis methods to predict the ageing and durability of concrete
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.ORCID iD: 0000-0002-8000-6781
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the societal demand for sustainability and the increasing age of infrastructure, a crucial task for the civil engineering community is to improve the durability of concrete structures. This thesis aims to contribute to such development through theoretical studies using mathematical modelling and numerical simulations. During its service life, a concrete structure is subjected to many different actions, ranging from mechanical loads to chemical and physical processes. Hence, a sound modelling strategy requires multiphysics and the inclusion of coupled chemical and physical fields (e.g. temperature, moisture and cement hydration) in addition to methods that describe mechanical integrity of the material. Conditions and phenomena critical for concrete structures at hydropower facilities have been of particular interest to study.

The thesis presents several mathematical models of various complexity to describe the multiphysical behaviour of concrete using a material point description. A significant focus is on models that describe the mechanical behaviour of concrete where aspects such as ageing, cracking, creep and shrinkage are investigated. For the creep behaviour, a state-of-the-art model based on the Microprestress–Solidification (MPS) theory is reviewed and further developed. The appended papers (III to IV) presents a mathematical framework for the modelling of durability aspects of concrete based on multiphase porous media theory. The governing equations are derived with the Thermodynamically Constrained Averaging Theory (TCAT) as a starting point. It is demonstrated how this framework can be applied to a broad variety of phenomena related to durability; from the casting and hardening of concrete to the long-term absorption of water into air-entrained concrete. The Finite Element Methods (FEM) is used to solve the proposed mathematical models, and their capabilities are verified using experimental data from the literature.

The main research contribution is the development and evaluation of theoretical models that advance the understanding and improve knowledge of the ageing and durability of concrete and concrete structures. More precisely, it is shown how multiphysical models and the developed multiphase framework can be used to gain insights on the material behaviour of concrete at smaller scales while they are also applicable to structural-scale simulations. During all model development, the efficient solution of structural problems has been fundamental. Through case studies and several examples from the literature, it is exemplified how these models can be used to enhance the performance and thereby increase the durability of concrete structures.

Abstract [sv]

I och med samhällets krav på hållbarhet och den ökande åldern på infrastrukturkonstruktioner är en avgörande uppgift för byggindustrin att förbättra betongkonstruktioners beständighet. Syftet med denna avhandling är att bidra till en sådan utveckling genom teoretiska studier med hjälp av matematisk modellering och numeriska simuleringar. En betongkonstruktion utsätts under sin livslängd för många olika mekaniska laster samt fysikaliska och kemiska processer. Ett sunt tillvägagångsätt gällande modellering kräver därför multifysik och kopplade fysikaliska och kemiska fält (t.ex. temperatur, fukt och cementhydratisering) beaktas utöver de metoder som beskriver materialets mekaniska hållfasthet. Sådana förutsättningar och fenomen som är kritiska för betongkonstruktioner vid vattenkraftsanläggningar är av särskilt intresse att studera.

Avhandling presenterar ett flertal matematiska modeller av varierande komplexitet baserade på en materialpunktsbeskrivning av betongens multifysikaliska beteende. En tonvikt ligger på modeller som beskriver betongens mekaniska beteende där aspekter som åldrande, sprickbildning, krypning och krympning undersöks. Gällande krypning har en state-of-the-art modell baserad på  “Microprestress–Solidification (MPS )” teorin studerats och vidareutvecklats. I de bilagda artiklarna (III till V) presenteras ett matematiskt ramverk för att beskriva fenomen relaterade till betongens beständighet. Detta ramverk baseras på en multifas beskrivning av porösa material, där de styrande ekvationerna är härledda utifrån “Thermodynamically Constrained Averaging Theory (TCAT)”. Det exemplifieras hur detta ramverk kan tillämpas på en rad olika fenomen relaterade till beständighet. Dessa sträcker sig från gjutning och hårdnande av betong till absorption av vatten till lufttillsatt betong. För att lösa de presenterade matematiska modellerna tillämpas den finita elementmetoden (FEM) och de numeriska lösningarna verifieras med hjälp av experimentella resultat från litteraturen.

Avhandlingens huvudsakliga forskningsbidrag är utveckling och utvärdering av teoretiska modeller som ökar förståelsen och förbättrar kunskapen om betong- och betongkonstruktioners åldrande och beständighet. Mer specifikt visas hur multifysiska modeller och det utvecklade multifas modellerna kan användas till att studera betongmaterialets beteende samtidigt som de också är användbara för simuleringar på strukturskala. En effektiv lösning av strukturproblem har varit viktig under all modellutveckling. I olika fallstudier och experiment från litteraturen exemplifieras hur dessa modeller kan användas för att förbättra betongkonstruktioners funktion och därigenom öka dess beständighet.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 123
Series
TRITA-ABE-DLT ; 1910
Keywords [en]
Ageing, Cracking, Creep, Concrete, Durability, Finite Element Method, Multiphysics, Shrinkage
Keywords [sv]
Beständighet, Betong, Finita elementmetoden, Krypning, Krympning, Multifysik, Sprickbildning, Åldring
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-246147ISBN: 978-91-7873-145-9 (print)OAI: oai:DiVA.org:kth-246147DiVA, id: diva2:1296357
Public defence
2019-04-11, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20190315

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-03-15Bibliographically approved
List of papers
1. Non-linear analyses of cracks in aging concrete hydro power structures
Open this publication in new window or tab >>Non-linear analyses of cracks in aging concrete hydro power structures
2016 (English)In: Dam Engineering, ISSN 0958-9341Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

The concrete structures at Swedish hydro power facilities were built during the early to mid-20th century and many of them are starting to exhibit age related wear and deterioration. It isimportant to ensure the integrity of these concrete structures from a dam safety perspectiveand also to secure a safe operation of the power facility in the future. With the latter in mind,this paper aims to study the concrete structures that house the power generating machinery ofthe facility, especially the parts close to the generator where the loads from the power unit aresupported. Cracks observed in these structures will reduce its stiffness, which affects theoperation of the rotating machinery. This paper presents and discusses some generalconsiderations and loads that are of importance for this type of structures and highlights sometypical cracks that have been observed in Swedish hydro power facilities. To complement thisdiscussion, a case study is presented of a hydro power facility where cracks have been foundin the concrete support structure of the power unit, especially at the interconnections betweenthe unit and the concrete. The most likely cause of these cracks are investigated through nonlinearfinite element analysis considering mechanical loads as well as physical loads such asdrying shrinkage and temperature variations. It is concluded that the long-term physicalloading is the most probable cause of the observed cracks. However, the operation of thepower unit and changes in its operational pattern can cause further propagation of thesecracks. Finally, suggestions on possible enhancement of the analysis methods used in the casestudy are proposed and discussed for further studies of this type of concrete structures.

Place, publisher, year, edition, pages
International Water Power & Dam Construction, 2016
Keywords
concrete, hydro power, cracks, finite element analysis, non-linear, drying shrinkage, thermal strains
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-186144 (URN)
Note

QC 20160503

Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2019-03-15Bibliographically approved
2. A coupled hygro-thermo-mechanical model for concrete subjected to variable environmental conditions
Open this publication in new window or tab >>A coupled hygro-thermo-mechanical model for concrete subjected to variable environmental conditions
2016 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 91, p. 143-156Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
concrete, multiphysics, moisture, temperature, creep, shrinkage, cracking, finite element analysis
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-186151 (URN)10.1016/j.ijsolstr.2016.03.004 (DOI)000377725800012 ()2-s2.0-84969705164 (Scopus ID)
Note

QC 20160503

Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2019-03-15Bibliographically approved
3. On the behaviour of con-crete at early-ages: A multiphase description of hygro-thermo-chemo-mechanical properties
Open this publication in new window or tab >>On the behaviour of con-crete at early-ages: A multiphase description of hygro-thermo-chemo-mechanical properties
2019 (English)In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 116, p. 202-216Article in journal (Refereed) Published
Abstract [en]

Understanding the early-age behaviour of concrete is of importance for designing durable concrete structures. To contribute to the improvement of this, a hygro-thermo-chemo-mechanical model is presented that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is based on a multiphase porous media framework, using the Thermodynamically Constrained Averaging Theory (TCAT) as starting point to derive the governing equations of the system. This allows for a systematic treatment of the multiscale properties of concrete and how these develop during hydration, e.g. chemical and physical fixation of water. The proposed mathematical model is implemented within the context of the Finite Element Method (FEM), where all physical fields are solved in a fully-coupled manner. Chosen properties of the model are demonstrated and validated using three experimental results from the literature. Generally, the simulated results are in good agreement with the measurements.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Hydration, Microstructure, Creep, Shrinkage, Modeling
National Category
Infrastructure Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-240363 (URN)10.1016/j.cemconres.2018.09.009 (DOI)000457667500023 ()2-s2.0-85057608758 (Scopus ID)
Note

QC 20190109

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-03-15Bibliographically approved
4. Three-dimensional simulations of ageing concrete structures using a multiphase model formulation
Open this publication in new window or tab >>Three-dimensional simulations of ageing concrete structures using a multiphase model formulation
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The durability of concrete structures is in no small degree determined by the quality and integrity of the concrete, where structural damages such as cracks negatively affect many of the functions of the structure. Often cracks are formed due to restrained thermal and hygral deformations, where the risk is exceptionally high during the early stages after casting. This study presents a hygro-thermo-chemo-mechanical model that accounts for phenomena such as hydration, external and internal drying, self-heating, creep, shrinkage and fracture. The model is derived as a modified version of a fully-coupled multiphase model recently proposed by Gasch et al. (2019) and implemented in the Finite Element Method. Here the governing equations are simplified, and a more efficient solution method is proposed. These modifications are made with the intention to obtain a model more suitable for structural scale simulations. To validate the model, one of the end-restrained beams tested within the French research project CEOS.fr is analyzed. Laboratory data on the concrete is used to calibrate to model and recordings of ambient conditions makes it possible to define accurate boundary conditions. Results from the simulation are compared to measured temperatures and deformations from the first 60 days after casting and are found to generally be in good agreement. Compared to the fully-coupled model by Gasch et al. (2019), the modifications proposed in this study reduce the computational cost by a factor five; without any noticeable differences to the structural results.

Keywords
Concrete, Early-age, Finite Element Method, Hygro-thermo-chemo-mechanical, Structural application
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-246007 (URN)
Note

QC 20190318

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-18Bibliographically approved
5. A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete
Open this publication in new window or tab >>A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete
2019 (English)In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 127, no 1, p. 113-141Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Netherlands: Springer, 2019
Keywords
Air-entrained concrete, Multiphase model, Long-term absorption, Diffusion, Pore size distribution
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-240364 (URN)10.1007/s11242-018-1182-3 (DOI)000459472600005 ()2-s2.0-85055973654 (Scopus ID)
Note

QC 20190108

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-03-19Bibliographically approved

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