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A Hygro-Thermo-Mechanical Multiphase Model for Long-Term Water Absorption into Air-Entrained Concrete
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.ORCID iD: 0000-0002-4015-3373
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.ORCID iD: 0000-0002-8000-6781
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
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. Vol. 127, no 1, p. 113-141
Keywords [en]
Air-entrained concrete, Multiphase model, Long-term absorption, Diffusion, Pore size distribution
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-240364DOI: 10.1007/s11242-018-1182-3ISI: 000459472600005Scopus ID: 2-s2.0-85055973654OAI: oai:DiVA.org:kth-240364DiVA, id: diva2:1271398
Note

QC 20190108

Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-03-19Bibliographically approved
In thesis
1. Multiphysical analysis methods to predict the ageing and durability of concrete
Open this publication in new window or tab >>Multiphysical analysis methods to predict the ageing and durability of concrete
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
Ageing, Cracking, Creep, Concrete, Durability, Finite Element Method, Multiphysics, Shrinkage, Beständighet, Betong, Finita elementmetoden, Krypning, Krympning, Multifysik, Sprickbildning, Åldring
National Category
Civil Engineering
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-246147 (URN)978-91-7873-145-9 (ISBN)
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

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Gasch, TobiasAnsell, Anders

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