L. Buffo-Lacarrière

Application of thermo-hydro-chemo-mechanical model for early age behaviour of concrete to experimental massive reinforced structures with strain–restraining system

This paper presents the application of a thermo-hydro-chemo-mechanical (THCM) model to the design of actual massive structures with a system to restrain the strain at early age (thermal strains and autogenous shrinkage). The experimental campaign was performed in the French national project CEOS.fr. The modelling of early-age behaviour of reinforced concrete is first based on a hydration model, which is able to reproduce the variations of temperature, water content and mechanical properties according to hydration. Then a non-linear mechanical model is used (combining creep and damage models, both adapted to hardening concrete). The comparison between numerical results (obtained with a calculation time of around 12 h on an ordinary computer) shows that the models are able to reproduce the early-age behaviour of restrained reinforcement concrete structures (in terms of strains, global forces and crack patterns). Using steel-concrete interface elements (adapted to early age), the models are also able to reproduce the influence of reinforcement on cracking.

Restrained shrinkage of massive reinforced concrete structures: results of the project CEOS.fr

Within the CEOS.fr national research project, several experiments on massive concrete structures were conducted to improve the knowledge on the cracking phenomenon. In this paper, experiments where deformations at early age are restrained are presented. Testing bodies are I-shaped and two largely dimensioned steel struts are placed laterally between the two transverse heads to prevent almost any shrinkage. Three testing bodies were realized: RG8, the reference one; RG9, with a reduced reinforcement and RG10, with an increased cover. A full set of measurement was used for auscultation of these beams during early age. Optical long base fibres gave information on the relative displacement of the central part of the beam. Local measurements of strains in concrete were given thanks to Vibrating Wire Extensometers. Gauges on rebars produced data of the strain on the first reinforcement layer, and the force in struts was monitored. With this, the force and stresses in concrete and rebars could be deduced. This huge amount of data allows verifying the phenomenology of the concrete. Various hypotheses were analysed to explain the strain measured and the corresponding forces in each component during specific period of early age. A first analysis of the cracking process shows that the cracks could appear for stresses below the tensile strength.

Material and Geometric Heterogeneity Consideration for Cracking Risk Prediction of Young Age Behavior of Experimental Massive Reinforced Concrete Structure

This article presents the application of a thermo-hydro-chemo-mechanical (THCM) model to a real complex structure of reactor confinement (mock-up VERCORS from EDF) by taking into account the specificities of the construction (construction consequences), the distributed reinforcements and the material heterogeneity of massive structure. The experimental campaigns were conducted during and after the construction of VERCORS. The early-age behavior of concrete is first modelled based on a multiphasic hydration model to ensure the thermal evolution. Then a 3D mechanical model is used to predict the consequences of hydration, temperature and water variations on mechanical behavior. An alternative approach to consider the structural effect of distributed reinforcement without explicit meshing of reinforcements is implemented and is able to reproduce the influence of reinforcement on the crack patterns. Moreover, the “Weakest link localization” method is also adapted to deal with a probabilistic scale effect due to the material heterogeneity of massive structure. It permits to assess directly the most likely tensile strength which can treat the first crack in softening part of the loaded volume of structures.

Requirements for the Modeling of Medium-Term Behavior of Nuclear Containment Concrete for a “Loss of Coolant Accident” Analysis

The objective of this research is to understand the behavior of concrete subjected to temperatures up to 180°C and to gas absolute pressures up to 5 bars applied during the two weeks envisioned in the “loss of coolant accident” (LOCA) scenario. Previous studies about delayed mechanical behavior of concrete have pointed out an increase of delayed strains with the temperature rise: the basic creep can be multiplied by a factor 10 at 80°C, and coupling between creep and heating can lead to damage and to transient thermal creep. These phenomena could be predominant if the LOCA induced conditions are maintained several days and more probably several weeks. So, a model able to predict the cracking and the gas leakages has to be developed. It has to consider these phenomena and their coupling with other possible causes of concrete damage previous to the LOCA. In fact, if the LOCA occurs on structure already damaged by early age cracking or endogenous chemical reactions, such as AAR or ettringite, the leakage risk could be increased. The paper will focus on some important aspects of these phenomena (creep rate dependency on temperature, scale effects at early age, damage induced by swelling reactions), and on their coupling in a finite element model.

Application structurale d'un modèle THCM pour le béton au jeune âge

ABSTRACT This paper presents a model predicting the early age cracking of structures. It is a promising tool to help industrials choose the materials and the construction techniques which reduce the cracking risk. The proposed model uses a multiphasic modelling of binder hydration predicting the hydration development of several anhydrous species (clinker, fly ash, silica fume…). The results of this first modelling are used as input data for a mechanical modelling of the non linear behaviour of concrete at early age (evolution of mechanical properties, creep, and damage).