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Samtidig temperatur- och fuktrörelser i ung betong
2014 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Basic shrinkage is the free contraction of a concrete body during the hydration of concrete, with exception of the movements caused by thermal dilation and moisture-exchange with the concrete body’s surrounding environment. For concretes with low w/s-ratios (low amount of blending water compared to cement), basic shrinkage is an significant factor concerning crack-risks in young concrete.There exist two models for calculation of basic shrinkage that has been developed at LTU (Luleå University of Technology) based on the maturity concept, but their accuracy can be questioned as they have not been tested against different temperature developments. The goal for this master thesis is, therefore, to control, or give a basis for, if these models are accurate or not, and if the temperature development affects the magnitude of basic shrinkage or not regarding the tested concrete. The used test method itself is also evaluated.To get a understanding for the problem a literature study was done about basic shrinkage, related phenomenon and existing models used at LTU. Tests have then been performed on the new base concrete “BAS2” through measurements of shrinkage and relative humidity done with several different temperature developments. Relative humidity has relevance as self-desiccation is a strongly contributing factor to the magnitude of the basic shrinkage. The existing models are then used to interpret and analyze the measured results. The results from measurement of shrinkage show that the second model that has been developed at LTU works significantly better than the first, and that good individual fitting is possible for all temperature developments individually. However, it is not possible to get one good fitting for all temperature developments, especially at low temperatures. The “bad” fitting seems to be more because of that the thermal dilation shows different properties at the different tests, rather than that the basic shrinkage necessarily is described wrong. Comparison of the basic shrinkage between the different tests also indicates that the basic shrinkage is increased with higher temperatures and decreased with lower, even after maturity has been considered. The relative humidity measurements are considered to be subjected to large margin of errors, but the received results points to trend that the rate of self-desiccation is higher at lower temperatures.The conclusions that can be made is that model II is best suited to describe basic shrinkage, but it has to be adjusted to be better, probably it’s how the thermal dilation is calculated that needs changing. The test equipment should be equipped with another strain gauge and more tests than on the current two samples must be performed to be able to make an evaluation that accurately describes basic shrinkage at different temperature developments. There should possibly be a test performed to determine thermal properties. The magnitude of basic shrinkage is affected by which temperature the concrete is exposed to, even after maturity has been considered.

Place, publisher, year, edition, pages
Keyword [en]
Keyword [sv]
Teknik, Autogen krympning, basic shrinkage, autogenous shrinkage, autogenous deformation, Thermal dilation, young concrete, ung betong, relativ fuktighet, relative humidity
URN: urn:nbn:se:ltu:diva-56456Local ID: d38f661e-7262-4e03-8449-10469ac09217OAI: diva2:1029843
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20140827 (global_studentproject_submitter)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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