Eric Bourdarot

Combination of Structural Monitoring and Laboratory Tests for Assessment of Alkali-Aggregate Reaction Swelling: Application to Gate Structure Dam

Southwestern Frances Temple-sur-Lot Dam, a gate structure built in 1948, has been subjected to continuous alkali-aggregate reaction (AAR)-induced displacements since 1964, despite nonsignificant residual swelling test results and low and relatively constant alkali content in the concrete. It has been assumed that this long-term behavior could be explained through a substitution process between calcium and alkali in the alkali-aggregate reactive gel. The calcium substitution phenomenon cannot be detected through a conventional residual swelling test since it is very slow, so an original AAR kinetics and residual swelling capability assessment method is proposed. A laboratory test dealing with silica consumption kinetics is first involved in this methods, and a numerical finite element inverse dam analysis, including laboratory measured consumption kinetics, is involved as a second step in this method. At a given period, only one observed structural displacement rate fit the final swelling amplitude. Comparison between instrument point displacement predicted by the calculations (not used for the fitting) and dam measured variations provided model prediction capability validation. Finally, future dam displacement and damage field prediction calculations were performed.

Creep, Shrinkage, and Anisotropic Damage in Alkali-Aggregate Reaction Swelling Mechanism-Part I: A Constitutive Model

Modeling the behavior of alkali aggregate reaction (AAR)damaged concrete is made complex by the large number of elementary physical phenomena to be taken into account (concrete reactivity, thermal activation, moisture dependence, concrete rheology, and damage interaction). This paper presents the elementary physical principles that lead to the formulation of a visco-elasto-plastic orthotropic damage model including chemical pressure induced by AAR. Particular attention is also paid to the modeling of moisture effects on AAR development and on drying shrinkage. The constitutive modeling proposed is developed into the framework of an anisotropic damage theory to realistically model the strong cracking anisotropy and swelling observed on affected reinforced beams. This paper is followed by a second one in which a calibration procedure is given for the model parameters and experimental results are used to verify the capability of the model to describe the mechanical behavior of degraded structures under various environmental and loading conditions.

Creep, Shrinkage, and Anisotropic Damage in Alkali-Aggregate Reaction Swelling Mechanism-Part II: Identification of Model Parameters and Application

This paper deals with parameter identification and model application of a finite element procedure developed for analysis of concrete structures affected by alkali-aggregate reaction (AAR). Theoretical aspects of the model (constitutive laws and underlying assumptions) have been presented and discussed in Part I of this study. The particularity of the model is the coupling between AAR, creep, shrinkage, and anisotropic damage. The first section of this study provides a calibration procedure for the model parameters. Then, an application of the model is carried out on degraded reinforced concrete beams under changing and inhomogeneous moisture conditions. The main results concern the capability of the model to reproduce simultaneously strong anisotropic swelling, damage observed during experiments, and structural displacements. A final discussion highlights the influence of oriented cracking induced by restrained AAR swelling on stress states.

French recommendations for limit-state analytical review of gravity dam stability

ABSTRACT This article presents the recent French recommendations drawn up by FRCOLD for the design of gravity dams. Recognising the disparities in the approaches of the various dam engineering bodies, the recommendations aim at harmonising practices to arrive at a standard approach. They adopt the same limit state design method as already used in the Eurocodes, with particular emphasis on cracking and shear strength limit states. They define a series of new parameters which were not introduced in earlier methods such as characteristic strength of materials, partial factors of safety and inclusion of new design situations. The background to the new format is the probabilistic concept of the acceptable design requirements. These recommendations are applied to an existing concrete gravity dam and the results are compared with other international guidelines.

DEF modelling based on thermodynamic equilibria and ionic transfers for structural analysis

Delayed ettringite formation (DEF) is a process which can lead to swelling and cracking of concrete. This paper proposes a chemical model to predict the kinetics and the amount of DEF in concretes subjected to high-temperature curing. The modelling considers several types of phenomena: the thermodynamic equilibria of hydrate crystallisation, the binding of ionic species to hydrated calcium silicates and the mass balance equations, which include the diffusion mechanisms. All the constitutive equations are provided and the thermodynamic constants found from a wide-ranging literature review are given in particular detail. The model has been implemented in a finite element code. The numerical results give the amount of ettringite and monosulphates, and ionic concentration fields in the simulated structure. They are compared with experimentation in which the early-age thermal cycle and long-term alkali release combine to cause DEF.

Effets structuraux de l'alcali reaction : Apports d'une experimentation sur elements de structures a la validation de modeles

ABSTRACT Assessment of ASR-damaged structures is a major concern for bridge and dam owners in France. Thus, validated models are needed in order to predict the behavior and residual bearing capacity of such works. With this aim, a large experimental program was carried out at the LCPC with EDF as a partner. Measurements were taken from the behavior of structures and specimens placed in various moisture and mechanical environments in order to realize a complete data bank. The mechanical analysis of the measurements showed the significance of ASR-induced strains anisotropy due to stresses, and moisture effect on ASR-induced expansion amplitude, on predicted behavior. They appear to be the main parameters to be accounted for in order to obtain good predictive models.

Sensibilité aux paramètres aléatoires d'un modèle pour le calcul des structures en béton atteintes par la réaction alcali-silice

ABSTRACT Concrete structures affected by alkali silica reaction deteriorate slowly. Damage kinetic and amplitude are modelled in the purpose to know their residual safety margin at various terms. Numerical modelling used includes several phenomena that involve a large number of material parameter to assess. The sensitivity study presented in this paper tries to draw the more influent parameters in order to assess them with a particular attention.

Etude expérimentale et modélisation de l'influence de l'eau sur la réaction alcali-silice

ABSTRACT Water is very important for alkali-silica reaction, it is the diffusion medium for ionic species and in the same time it is part of the reaction products. The work presented in the following article deals with a new method which takes into account the effect of water on alkali-aggregate reaction thanks to original laws. The latter have been determined thanks to experimental results. The modelling is validated by the means of numerical simulations of experiments carried out on purpose or taken from litterature.

Modélisation chimique de la réaction alcali-silice: prise en compte de l'influence de la distribution granulaire réactive

ABSTRACT Nowadays, knowledge about ASR mechanisms is good enough to prevent new cases. Nevertheless a numerical tool seems necessary for all affected structures. This article deals with a new modelling based on the description of alkalis and calcium transport within concrete. It takes into account the effect of the size and distribution of reactive aggregates. Results from an experimental campaign and corresponding numerical simulations are presented and compared.