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Open AccessArticle

Double Feedback Control Method for Determining Early-Age Restrained Creep of Concrete Using a Temperature Stress Testing Machine

by He Zhu, Qingbin Li *, Yu Hu * and Rui Ma
State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China
*
Authors to whom correspondence should be addressed.
Materials 2018, 11(7), 1079; https://doi.org/10.3390/ma11071079
Received: 1 May 2018 / Revised: 20 June 2018 / Accepted: 20 June 2018 / Published: 25 June 2018
(This article belongs to the Special Issue Brittle Materials in Mechanical Extremes)
Early-age restrained creep influences the cracking properties of concrete. However, conventional creep measurements require a large number of tests to predict the restrained creep as it is influenced by the combined effects of variable temperature, creep recovery, and varying compression and tension stresses. In this work, a double feedback control method for temperature stress testing was developed to measure the early-age restrained creep of concrete. The results demonstrate that the conventional single feedback control method neglects the effect of restrained elastic deformation, thus providing a larger-than-actual creep measurement. The tests found that the double feedback control method eliminates the influence of restrained elastic deformation. The creep results from the double feedback method match well with results from the single feedback method after compensation for the effects of restrained elastic deformation is accounted for. The difference in restrained creep between the single and double feedback methods is significant for concrete with a low modulus of elasticity but can be neglected in concrete with a high modulus of elasticity. The ratio between creep and free deformation was found to be 40–60% for low, moderate, and high strength concretes alike. The double feedback control method is therefore recommended for determining the restrained creep using a temperature stress testing machine. View Full-Text
Keywords: restraint; creep; double feedback method; concrete; temperature stress testing machine (TSTM) restraint; creep; double feedback method; concrete; temperature stress testing machine (TSTM)
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Zhu, H.; Li, Q.; Hu, Y.; Ma, R. Double Feedback Control Method for Determining Early-Age Restrained Creep of Concrete Using a Temperature Stress Testing Machine. Materials 2018, 11, 1079.

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