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Thermal Crack Risk of Concrete Structures: Evaluation of Theoretical Models for Tunnels and Bridges
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
2017 (English)In: Nordic Concrete Research, ISSN 0800-6377, no 56, 55-70 p.Article in journal (Refereed) Published
Abstract [en]

An approach for thermal crack risk estimations was introduced in the Swedish design guidelines BRO 94. The cracking occurs during the early hardening process because of the exothermic reactions between water and cement and often result in high repair costs and delayed construction. This paper studies and validates the inherent safety levels for one typical case of concrete structure. Three slab-frame structures were analysed and the original crack risk estimations were compared to the actual cracking and postcalculations were carried out, using actual parameters. This paper shows that walls with computed strain ratios over 70% were affected by thermal cracks.

Place, publisher, year, edition, pages
Nordic Concrete Federation , 2017. no 56, 55-70 p.
Keyword [en]
Thermal cracking, Structural Design, Sustainability, Concrete tunnels
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-64967OAI: oai:DiVA.org:ltu-64967DiVA: diva2:1129785
Note

Validerad;2017;Nivå 1;2017-08-16 (rokbeg)

Available from: 2017-08-07 Created: 2017-08-07 Last updated: 2017-11-24Bibliographically approved
In thesis
1. Thermal Crack Risk Estimation and Material Properties of Young Concrete
Open this publication in new window or tab >>Thermal Crack Risk Estimation and Material Properties of Young Concrete
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents how to establish a theoretical model to predict risk of thermal cracking in young concrete when cast on ground or an arbitrary construction. The crack risk in young concrete is determined in two steps: 1) calculation of temperature distribution within newly cast concrete and adjacent structure; 2) calculation of stresses caused by thermal and moisture (due to self-desiccation, if drying shrinkage not included) changes in the analyzed structure. If the stress reaches the tensile strength of the young concrete, one or several cracks will occur.

The main focus of this work is how to establish a theoretical model denoted Equivalent Restraint Method model, ERM, and the correlation between ERM models and empirical experiences. A key factor in these kind of calculations is how to model the restraint from any adjacent construction part or adjoining restraining block of any type.

The building of a road tunnel and a railway tunnel has been studied to collect temperature measurements and crack patterns from the first object, and temperature and thermal dilation measurements from the second object, respectively. These measurements and observed cracks were compared to the theoretical calculations to determine the level of agreement between empirical and theoretical results.

Furthermore, this work describes how to obtain a set of fully tested material parameters at CompLAB (test laboratory at Luleå University of Technology, LTU) suitable to be incorporated into the calculation software used. It is of great importance that the obtained material parameters describe the thermal and mechanical properties of the young concrete accurately, in order to perform reliable crack risk calculations.  Therefore, analysis was performed that show how a variation in the evaluated laboratory tests will affect the obtained parameters and what effects it has on calculated thermal stresses.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2017. 85 p.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keyword
Thermal cracking risk, young concrete, Equivalent Restraint Method, strength development, heat of hydration, creep, shrinkage, thermal dilation, modeling, field observations
National Category
Construction Management
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-65495 (URN)978-91-7583-951-6 (ISBN)978-91-7583-952-3 (ISBN)
Presentation
2017-10-10, F1031, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-09-05 Created: 2017-09-05 Last updated: 2017-11-24Bibliographically approved

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