scholarly journals Modelling of Coupled Shrinkage and Creep in Multiphase Formulations for Hardening Concrete

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1745
Author(s):  
Peter Gamnitzer ◽  
Andreas Brugger ◽  
Martin Drexel ◽  
Günter Hofstetter
Keyword(s):  
Viscous Flow ◽  
Effective Stress ◽  
Drying Shrinkage ◽  
Shrinkage Strain ◽  
Viscoelastic Creep ◽  
Limit Value ◽  
Shrinkage And Creep ◽  
Mechanical Models ◽  
Term Response

The durability and serviceability of concrete structures is influenced by both the early-age behavior of concrete as well as its long-term response in terms of shrinkage and creep. Hygro-thermo-chemo-mechanical models, as they are used in the present publication, offer the possibility to consistently model the behavior of concrete from the first hours to several years. However, shortcomings of the formulation based on effective stress, which is usually employed in such multiphase models, were identified. As a remedy, two alternative formulations with a different coupling of shrinkage and creep are proposed in the present publication. Both assume viscous flow creep to be driven by total stress instead of effective stress, while viscoelastic creep is driven either by total or effective stress. Therefore, in contrast to the formulation based on effective stress, they predict a limit value for shrinkage as observed in long-term drying shrinkage tests. Shrinkage parameters for the new formulations are calibrated based on drying shrinkage data obtained from thin slices. The calibration process is straightforward for the new formulations since they decouple shrinkage and viscous flow creep. The different formulations are compared using results from shrinkage tests on sealed and unsealed cylindrical specimens. Shrinkage strain predictions are significantly improved by the new formulations.

Development of shrinkage resistant microfibre-reinforced cement-based composites

2012 ◽  
Vol 2 (2) ◽  
Author(s):  
P. Hamedanimojarrad ◽  
G. Adam ◽  
A. Ray ◽  
P. Thomas ◽  
K. Vessalas
Keyword(s):  
Drying Shrinkage ◽  
Shrinkage Strain ◽  
Crack Size ◽  
Moisture Loss ◽  
The Novel ◽  
Total Shrinkage ◽  
Low Concentrations ◽  
Reinforced Cement ◽  
Short And Long Term

AbstractDifferent shrinkage types may cause serious durability dilemma on restrained concrete parts due to crack formation and propagation. Several classes of fibres are used by concrete industry in order to reduce crack size and crack number. In previous studies, most of these fibre types were found to be effective in reducing the number and sizes of the cracks, but not in shrinkage strain reduction. This study deals with the influence of a newly introduced type of polyethylene fibre on drying shrinkage reduction. The novel fibre is a polyethylene microfibre in a new geometry, which is proved to reduce the amount of total shrinkage in mortars. This special hydrophobic polyethylene microfibre also reduces moisture loss of mortar samples. The experimental results on short and long-term drying shrinkage as well as on several other properties are reported. The hydrophobic polyethylene microfibre showed promising improvement in shrinkage reduction even at very low concentrations (0.1% of cement weight).

scholarly journals Strategies for improving dimensional stability of concrete

2016 ◽  
Vol 43 (10) ◽  
pp. 875-885
Author(s):  
P.L. Ng ◽  
Albert K.H. Kwan
Keyword(s):  
Dimensional Stability ◽  
Cement Content ◽  
Drying Shrinkage ◽  
Sustained Load ◽  
Early Age ◽  
Test Results ◽  
Dimensional Changes ◽  
Shrinkage And Creep ◽  
Concrete Mix

Changes in dimension of concrete due to early-age heat generation, long-term drying shrinkage, and creep under sustained load could lead to significant movements of the concrete structure and lock-up stresses if the movements are restrained. The lock-up stresses are often large enough to cause cracking and water leakage, thereby adversely affecting the serviceability and durability of the structure. Whilst the dimensional changes are quite variable because of their dependence on the environmental conditions and applied loads, they are all related to the concrete mix proportions. Generally, the dimensional stability of concrete can be improved by reducing its cement content and paste volume. Moreover, since the aggregate also shrinks, the dimensional stability can be improved by suppressing the shrinkage of aggregate as well. In this paper, strategies for improving the dimensional stability of concrete are formulated based on experimental research. Test results are presented to demonstrate their effectiveness and applicability.

Finite Element Modeling of Drying Shrinkage in Concrete Blending with Mineral Admixtures

2011 ◽  
Vol 368-373 ◽  
pp. 1588-1594
Author(s):  
Tie Cheng Wang ◽  
Quan Min Peng
Keyword(s):  
Critical Factor ◽  
Drying Shrinkage ◽  
Moisture Diffusion ◽  
Shrinkage Strain ◽  
Mineral Admixtures ◽  
Granulated Blast Furnace Slag ◽  
Moisture Field ◽  
Adopted Model ◽  
Long Term Behavior

Drying shrinkage is a critical factor influencing the long-term behavior of concrete. In this paper, related parameters for calculating moisture field are discussed based on the theory of nonlinear moisture diffusion. Numerical simulation of shrinkage tests of concrete blending with fly ash and ground granulated blast furnace slag is conducted by ANSYS, considering the solution analogy between moisture field and temperature field. The calculated shrinkage strains are in good agreement with experimental results and the adopted model and finite elements method can be used to predict the time-dependent moisture field and shrinkage strain field in the real structure.

Study on Strength, Shrinkage and Creep of Concrete Containing Ultrafine Fly Ash Composites

2012 ◽  
Vol 450-451 ◽  
pp. 162-167
Author(s):  
Bao Ju Liu ◽  
You Jun Xie
Keyword(s):  
Mechanical Properties ◽  
Fly Ash ◽  
Drying Shrinkage ◽  
Experimental Results ◽  
Steam Curing ◽  
Curing Conditions ◽  
Shrinkage And Creep

At steam curing and moist curing conditions, the mechanical properties of concrete with different fineness and different proportions ultrafine fly ash-slag composite were studied. The experimental results indicated that the addition of ultrafine fly ash-slag composite had improved the long term mechanical properties of steam-cured concrete. The concrete with ultrafine fly ash-slag composite has lower drying shrinkage and creep compared to that of control concrete.

Prediction Models of Shrinkage and Creep for Concrete Columns

2011 ◽  
Vol 243-249 ◽  
pp. 1583-1588
Author(s):  
Yi Gang Lv ◽  
Jian Ren Zhang ◽  
Kang Xu
Keyword(s):  
Prediction Models ◽  
Plain Concrete ◽  
Least Square Method ◽  
Concrete Columns ◽  
Shrinkage Strain ◽  
Least Square ◽  
Creep Effect ◽  
Shrinkage And Creep ◽  
Term Performance

In constant temperature and humidity environment, the properties of shrinkage and creep for a group of plain concrete and reinforced concrete columns were observed in long-term and experimental method. The curves of concrete shrinkage and creep effect with time were obtained. Checking coefficient and type coefficient of shrinkage and creep effect were put forward in order to predict models of shrinkage and creep. Using the least square method, functions of checking coefficient and type coefficient were acquired and the prediction models of shrinkage strain and creep coefficient of concrete were obtained based on the modification of the formula of JTG D62-2004. The foundation is laid for the application of the long-term performance research in bridge structure.

scholarly journals Adaptation of flocculent anammox culture to low temperature by cold shock: long-term response of microbial population

2021 ◽  
pp. 1-19
Author(s):  
Vojtech Kouba ◽  
Juan Camilo Gerlein ◽  
Andrea Benakova ◽  
Marco Antonio Lopez Marin ◽  
Eva Rysava ◽  
...  
Keyword(s):  
Low Temperature ◽  
Cold Shock ◽  
Microbial Population ◽  
Term Response

Unfolding the case of returnees: How the European Union and its member States are addressing the return of foreign fighters and their families

2021 ◽  
pp. 1-23
Author(s):  
Carlota Rigotti ◽  
Júlia Zomignani Barboza
Keyword(s):  
European Union ◽  
Perceived Threat ◽  
The European Union ◽  
Security Threat ◽  
Short Term ◽  
Member States ◽  
Foreign Fighters ◽  
Term Response

Abstract The return of foreign fighters and their families to the European Union has mostly been considered a security threat by member States, which consequently adopt repressive measures aimed at providing an immediate, short-term response to this perceived threat. In addition to this strong-arm approach, reintegration strategies have also been used to prevent returnees from falling back into terrorism and to break down barriers of hostility between citizens in the long term. Amidst these different strategies, this paper seeks to identify which methods are most desirable for handling returnees.

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