Abstract
This Part presents a refinement of the BP model for the effects of temperature on the basic creep and drying creep of concrete. The temperature effect on basic creep is introduced through two different activation energies, one for the effect of temperature increase on the rate of hydration, which causes a decrease of creep, and one for the effect of temperature increase on the rate of creep, which causes an increase of creep. The dichotomy of these two opposing temperature influences is an essential feature, required for good agreement with test data. The greatest error in basic creep is again caused by the prediction of the material parameters from concrete composition and strength. This error can be largely eliminated by conducting limited short-time basic creep tests at different temperatures. Comparisons with 13 different data sets from the literature show a satisfactory agreement, better than that achieved with previous models, while at the same time the scope of the present model is broader. The effect of temperature on the creep of drying specimens is rather different because heating causes a moisture loss from unsealed specimens. The paper presents prediction formulae which modify those for drying creep at room temperature on the basis of the activation energy concept and take into account the effect of heating on the moisture loss. Comparisons with the limited test data that exist show satisfactory agreement. No additional material parameters depending on concrete composition and strength are introduced for drying creep.
Resume
Dans ce volet, on présente un modèle BP perfectionné pour les effets de la température sur le fluage de base et le fluage au séchage du béton. L'effet de température sur le fluage de base se produit par l'intermédiaire de deux énergies d'activation différentes, une pour l'effet de l'accroissement de la température sur la vitesse de l'hydratation, qui cause une diminution du fluage, et l'autre pour l'effet de l'accroissement de la température sur la vitesse du fluage, qui cause un accroissement du fluage.
L'opposition de ces deux effets de la température constitue une caractéristique nécessaire pour une bonne concordance avec les données d'essai. L'erreur la plus importante dans le fluage de base reste due à la prédiction des paramètres du matériau à partir de la composition et de la résistance du béton, erreur qui peut être éliminée en effectuant des essais limités de fluage de base à court terme à des températures différentes.
Des comparaisons avec 13 séries d'essai différentes sélectionnées dans la littérature montrent une concordance satisfaisante, supérieure à celle obtenue avec les modèles précédents. Cependant, en même temps, le champ d'application de ce modèle est plus large. L'effet de la température sur le fluage des éprouvettes en cours de séchage est assez différent car le chauffage entraîne une perte d'humidité dans les éprouvettes à l'air libre.
On présente ici des formules de prédiction qui modifient celles utilisées pour le fluage en séchage à température ambiante sur la base du concept d'activation de l'énergie, et qui prennent en compte l'effet du chauffage sur la perte d'humidité. Des comparaisons avec les données d'essai limitées dont on dispose montrent une concordance satisfaisante. On n'a pas introduit d'autres paramètres du matériau en relation avec le comportement et la résistance du béton pour le fluage au séchage.
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Bažant, Z.P., Kim, JK. Improved prediction model for time-dependent deformations of concrete: Part 4—Temperature effects. Materials and Structures 25, 84–94 (1992). https://doi.org/10.1007/BF02472461
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DOI: https://doi.org/10.1007/BF02472461