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Thermal Crack Risk Estimations of Concrete Walls – Temperature and Strain Measurements Correlated to the Equivalent Restraint Method
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.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Self-induced non-elastic deformations in hardening concrete, caused by restrained volume changes due to thermal dilatation and moisture deformations, often leads to cracking. In thermal crack risk analyses, determination of the degree of restraint is vital. One model to estimate the restraint and calculate the thermal crack risk is the Equivalent Restraint Method, ERM. This method has previously been analysed but needs to be examined and validated further. Measurements of wall castings were performed and compared to calculations with ERM in order to establish a correlation to empirical observations. A satisfying correlation between theoretically estimated and measured time of through cracking was achieved. Based on this study and other, ERM is thus considered to work satisfyingly.

Keyword [en]
Thermal cracking, Early age concrete, Local restraint method, Equivalent restraint method, Modelling, Strain measurement, Field documentation.
National Category
Construction Management
Research subject
Construction Engineering and Management
Identifiers
URN: urn:nbn:se:ltu:diva-65493OAI: oai:DiVA.org:ltu-65493DiVA: diva2:1138415
Available from: 2017-09-05 Created: 2017-09-05 Last updated: 2017-09-05
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: 2017-09-25Bibliographically approved

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