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A look at the stress rate versus time of cracking relationship observed in the restrained ring test

Title: A look at the stress rate versus time of cracking relationship observed in the restrained ring test
Author(s): Emmanuel K. Attiogbe, Jason Weiss, Heather T. See
Paper category : conference
Book title: International RILEM Symposium on Concrete Science and Engineering: A Tribute to Arnon Bentur
Editor(s): J. Weiss, K. Kovler, J. Marchand, and S. Mindess
Print-ISBN: None
e-ISBN: 2912143926
Publisher: RILEM Publications SARL
Publication year: 2004
Nb references: 18
Language: English

Abstract: Portland cement based concrete experiences early-age volume changes in response to moisture changes, temperature changes, or chemical reactions. If these volume changes are restrained, tensile stresses can develop in the material, which ultimately can lead to cracking. Ring tests have historically been used to provide qualitative comparisons of the potential for restrained shrinkage cracking of concrete mixtures. Recent studies, however, have shown that instrumented ring tests can be used to quantify restrained shrinkage behavior and provide the basis for assessing the early-age cracking potential of various concrete mixtures.
In the analysis of the results of the restrained ring test an interesting relationship has been observed between the rate of stress at the time of cracking and the age at which cracking occurs. This paper investigates potential explanations for this relationship. A preliminary analysis of stress development for the case of uniform drying is presented where it is shown that stress rate is directly proportional to the shrinkage rate. Evidence is presented in which the effects of moisture gradients are considered to show that the time of cracking is related to the depth of the moisture gradient. This implies that the corresponding rate of sectional force development (i.e., “rate of average residual stress development”) is inversely proportional to the square root of drying time. Finally, data is presented that illustrates that the residual stress-to-strength ratio (i.e., a cracking index) is not a constant value. Rather it is proposed that the cracking index that causes failure decreases with longer drying times due to the effects of creep under a sustained load. A limiting ratio is presented which may be used to minimize the probability of restrained shrinkage cracking of concrete elements.

Online publication: 2004-03-25
Classification: Cracking
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2912143926.025

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