Abstract
At the Magnel Laboratory for Concrete Research, University of Ghent, Belgium, an extensive experimental programme was set up in order to study the basic creep behaviour of early age concrete. Tests were carried out for a loading age ranging from 12 hours to 14 days, 2ith two different stress levels: 20% and 40% of the compressive strength at the age of loading. Three different cement types were considered: one Portland cement and two blast furnace slag cements. Based on the experimental results a new fundamental model is proposed. The basic creep evolution is completely related to the evolution of the degree of hydration. Time is no longer an explicit parameter. The stress-strain non-linearity of the basic creep is correlated with the stress-strain non-linearity of the instantaneous deformation at loading. Furthermore, based on the fundamental basic creep model and following the principles of the equivalent time method a new degree of hydration based formulation for the early age basic creep under varying stresses is developed: the fictitious degree of hydration method. Simulations of experimental results show that this new method provides a good alternative for the traditional superposition method.
Résumé
Au laboratoire Magnel de Recherche sur le Béton (Université de Gand, Belgique), on a réalisé un vaste programme de recherche expérimentale concernant le fluage de base du béton en phase de durcissement. On a exécuté des essais de fluage à partir d'un âge variant de 12 heures à 14 jours, et ceci à deux niveaux de compression: 20% et 40% de la résistance en compression à l'âge de la mise en charge. Un ciment Portland et deux ciments de haut fourneau ont été pris en considération. Sur la base des résultats expérimentaux, on a établi un nouveau modèle fondamental non linéaire. Ce modèle décrit la relation entre l'évolution du fluage de base du béton jeune et l'évolution du degré d'hydratation. Le temps n'intervient plus d'une manière explicite. En plus, il y a une corrélation entre la non-linéarité du fluage de base et celle de la déformation instantanée. Ensuite, sur la base de ce nouveau modèle et par analogie avec la méthode du temps équivalent, on a établi une nouvelle méthode: celle du degré d'hydratation fictif. Plusieurs essais de fluage sous contrainte variable ont permis de constater que la nouvelle méthode est une alternative valable pour la méthode de superposition.
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Abbreviations
- A:
-
parameter
- a:
-
parameter
- b:
-
parameter
- c1 :
-
parameter
- c2 :
-
parameter
- Eco :
-
Young's modulus
- fc :
-
concrete strength
- r:
-
degree of hydration
- rb :
-
degree of hydration at loading
- rbf :
-
fictitious degree of hydration
- t:
-
time
- tb :
-
loading age
- tbf :
-
fictitious loading age
- ± b :
-
stress level at loading
- ε c :
-
strain
- ε cc :
-
creep strain
- ε c0 :
-
instantaneous deformation at loading
- ε c1 :
-
strain at peak stress
- ν:
-
normalized strain
- σ:
-
stress
- σ c :
-
compressive stress
- ϕ c :
-
creep coefficient
- Φ:
-
creep function
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Editorial Note Prof. Dr. Ir. Luc Taewe is a RILEM Senior Member. Prof. Dr. Ir. Geert De Schutter is a RILEM Affiliate Member. He participates in the work of RILEM TC EAS: ‘Early age shrinkage induced stresses and cracking in cementitious systems’.
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De Schutter, G., Taerwe, L. Fictitious degree of hydration method for the basic creep of early age concrete. Mat. Struct. 33, 370–380 (2000). https://doi.org/10.1007/BF02479646
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DOI: https://doi.org/10.1007/BF02479646