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Evaluation of Material Properties for Young Concrete
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]

Restrained volumetric changes in early age concrete may cause tensile strength failure, i.e. crack initiation and propagation. The volumetric changes are primarily induced by a change in thermal and moisture states, and it is of great importance to quantify the resulting stresses and strains that arise when the volumetric changes are restrained. Large economical and technical benefits are gained if measures to avoid cracking can be determined by calculations prior to casting. To perform such calculations, the following property areas of the concrete needs to be known; strength development, heat of hydration, basic shrinkage, thermal dilation, basic creep and stress at full restraint.

 

This work demonstrates how the concrete can be tested in a laboratory environment and how to evaluate the numerical data, thus yielding a parameter set that may be used during stress and strain development calculations. Furthermore, a brief investigation is performed on how sensitive the evaluation for each test is, with respect to crack risk estimation.

 

It is showed that the measured stress development from the stress development at full restraint test can be considered as a checkpoint for the total parameter set. The reason is that the calculated stress development, which is compared to the measured counterpart, is influenced by all evaluated parameters.

 

It is discussed that out of the performed tests, three are of significant importance when it comes to provide an operational parameter set for the calculations. These tests are the ones achieving strength development, heat of hydration and stress at full restraint.

Keyword [en]
Young concrete, material parameters, strength development, heat of hydration, basic creep, basic shrinkage, thermal dilation, modelling, stress at full restraint
National Category
Construction Management
Research subject
Construction Engineering and Management
Identifiers
URN: urn:nbn:se:ltu:diva-65494OAI: oai:DiVA.org:ltu-65494DiVA: diva2:1138419
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: 2017-11-24Bibliographically approved

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