Stephane Poyet

Atomic Energy and Alternative Energies Commission | CEA · Département de Physico-Chimie (DPC)

Coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) approaches may be important for assessing the long-term durability of cementitious materials. We present a multiphysics approach to overcome past limitations of THMC modelling and validate it based on experimental results of accelerated carbonation tests. Our numerical approach rests on a sequent...

Thermal desorption is a critical process in cement-based materials subjected to temperature increase. C-S-H surface is the most likely surface available for thermal desorption in these materials. Here, we investigate surface thermal desorption in C-S-H. Molecular simulations are used to get systems equilibrated under two drained poromechanical cond...

Alkali‐activated materials (AAMs) are considered a promising alternative to materials made from ordinary Portland cement (OPC). Other than considering the durability of the material itself, the use of AAMs for reinforced concrete elements also raises the question of steel corrosion processes in these materials, which are still relatively unknown. T...

Coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) approaches are crucial for assessing the durability of cementitious materials. We present a novel approach to overcome past limitations of THMC modelling and validate it based on experimental results of accelerated carbonation tests. Our numerical approach rests on a sequential coupling between H...

This modelling study investigated the physicochemical and kinetic controls of the mineralogical evolutions of cementitious materials subject to accelerated atmospheric carbonation. Simulations are based on published experimental results on two samples, a hydrated C3S and a C-S-H paste, carbonated for 1 year at 55 % RH at 3 % CO2. For the C3S paste,...

Cement-based materials are more and more recognized as fractal materials. From a practical point of view, fractality means that the pore size distribution can be described using fractal scaling law (i.e. power functions). Here, the simplest scaling law making use of a single fractal dimension was used to generate simple and virtual fractal porous m...

The effect of temperature on water vapour desorption isotherms can be described simply using the Clausius-Clapeyron equation and the isosteric energy of adsorption, the latter conventionally estimated using two (or more) isotherms obtained at different temperatures. This approach has some disadvantages, however, and this article puts forward a simp...

Durabilité des structures en béton armé : séchage, carbonatation et corrosion

This study explored the reactive processes of atmospheric carbonation and the consequences with respect to cementitious materials. Two model pastes were used: hydrated C3S (including C-S-H and portlandite) and a paste prepared by hydrating a blend of C3S and nanosilica (including C-S-H only). The two pastes were carbonated under accelerated conditi...

Model synthetic pastes were designed to obtain a simplified silica system that could be used in durability studies on materials with low calcium-to-silica ratios. The synthetic pastes made use of the well-known pozzolanic reaction between tricalcium silicate (C3S) and nanosilica, covering calcium-to-silica ratios (C/S) from 0.8 to 3.0. The pure C3S...

The durability assessment of cementitious materials and concrete subjected to atmospheric carbonation of concrete has been an extensive study of research. Experimental studies on the subject show, among other results, that the response depends strongly on the cement composition. This paper focuses on two model materials: an hydrated C3S paste and a...

When considering the early-age behavior of massive concrete structures, it is important to accurately reproduce the evolutions of the mechanical properties and their evolutions as a function of the hydration state. In this paper, we propose a method based on data gathered in an extensive experimental campaign to estimate the mechanical properties o...

The influence of atmospheric carbonation on gas diffusion was investigated using four hardened cement pastes (CEM I, CEM III/A, CEM V/A, and a low-alkalinity binder) with common water-to-binder ratio (0.4). The diffusivity of the non‑carbonated and carbonated pastes with respect to helium and nitrogen was measured at different relative humidities....

The differences in unsaturated permeability between concrete prepared in the laboratory (labcrete) and on a real construction site (fieldcrete) were investigated experimentally and using inverse analysis. Although more porous, the fieldcrete specimens were shown to have an average permeability very close to the labcrete ones. The fieldcrete permeab...

Cracks are inevitable in reinforced concrete structures and promote the diffusion of aggressive agents towards the reinforcement. In Eurocodes, for some exposure conditions, a threshold not to be exceeded for crack width near the rebar is recommended in order to limit risks of corrosion development and ensure structure durability. On the other hand...

The aim of this research was to evaluate the ability of carbonated mortar prepared with calcium sulfoaluminate (CSA) cement to provide corrosion protection to embedded steel. Reference mortar with ordinary Portland cement (OPC), mortar with low-pH binder (fly ash and silica fume) and mortar with CSA cement were exposed to accelerated carbonation fo...

The impact of temperature on carbonation was investigated in laboratory conditions using a device developed for this purpose. Two hardened cement pastes (CEM I and CEM V/A) were tested between 20 °C and 80 °C at different levels of relative humidity (RH). The carbonation rate of the CEM I increased with temperature, whereas that of CEM V/A reached...

Cement based materials are widely used as binding matrices for radionuclides in low and intermediate level waste management applications. We studied the effect of irradiation and carbonation under atmospheric condition on the leaching of Sr from Portland cement paste. Samples were exposed to gamma irradiation or subjected to thermal treatment under...

The consequences of accelerated carbonation at 3% CO2 were compared with those of natural carbonation (0.04%). Cement pastes (CEM I and CEM V/A) as well as the three major constitutive phases (C-S-H of different C/S ratios, portlandite and ettringite) were used and changes in the mineralogy, microstructure, water retention and cracking were investi...

The ability of carbonated mortar to provide corrosion protection of embedded steel was studied on mortars prepared with low-alkalinity binders. Three mortars were investigated, mortar based on ordinary Portland cement, mortar based on high volume of fly ash and silica fume and mortar based on slag and nano-silica. Analysis of impedance spectra afte...

Reinforced concrete is widely used in the construction of buildings, historical monuments and also nuclear power plants. For various reasons, many concrete structures are subject to unavoidable cracks that accelerate the diffusion of atmospheric carbon dioxide to the steel/concrete interface. Carbonation at the interface induces steel corrosion tha...

Corrosion is the major degradation pathway affecting reinforced concrete structures. In the long-term, the rust layer might become thick and slow down the diffusion of oxygen from the atmosphere to the steel. With this in mind, the mineralogy, microstructure and diffusion properties of an old and thick corrosion product layer were investigated. Des...

Reinforced concrete is widely used in the construction of buildings, historical monuments, infrastructures and nuclear power plants. For a variety of reasons, many concrete structures are subject to unavoidable cracks that accelerate the diffusion of atmospheric carbon dioxide to the steel/concrete interface. Carbonation at the interface induces st...

Among the necessary data in the description of the transport of water, the retention curve is a vital piece of information whose characterization can turn out to be long and fastidious. Within this framework, sorption balance is being put to use more and more often in laboratories. These experimental devices enable a faster onset for water balance...

A simple, analytical model was proposed to account for the effect of moderate temperature on water retention in cement-based materials. The model takes advantage of the simplicity and flexibility of van Genuchten equation. It was first calibrated using experimental results taken from literature and then successfully validated on other results. The...

A semi-analytical model of hydration kinetics based on the boundary nucleation and space-filling growth for early hydration and a diffusion-controlled kinetics for late hydration is proposed. The objective is to develop a simple model that can be coupled with more complex approaches required for the estimation of properties at early-age, but withou...

Describing water transport in concrete is an important issue for the durability assessment of radioactive waste management reinforced concrete structures. Due to the waste thermal output such structures would be submitted to moderate temperatures (up to 80 °C). We have then studied the influence of temperature on water transport within hardened cem...

In unsaturated conditions, the durability of concrete structures is strongly dependent on the evolution of the amount of free water within concrete porosity. Reliable durability assessment of concrete structures in relation to their environment thus requires accurate unsaturated water transport description as well as reliable input data. The effect...

This paper presents an experimental program allowing determining the effect of cracks and their orientations on initiation and propagation of reinforcement steel corrosion due to carbonation. The influence of different environmental conditions will be tested in order to propose an operational model allowing the evaluation of the kinetic of corrosio...

This paper presents an experimental program allowing determining the effect of pre-cracks and their orientations on both initiation and propagation of reinforcement steel corrosion due to carbonation in different environmental conditions, in order to propose an operational model allowing the evaluation of the kinetic of corrosion of the reinforceme...

Moisture has an impact in many of the degradation mechanisms that appear in the structures of a nuclear power plant. Moisture conditions in a reactor containment wall have been simulated by using a hygrothermal model of drying concrete. Methods to estimate the temperature dependency of the sorption isotherms and moisture transport properties is sug...

In the framework of the DOPAS European project, the French agency for radioactive waste management (Andra) has recently undertaken a research program aiming at proving the technological feasibility of deep repository sealing: the Full Scale Sealing experiment (FSS). This operation involves the fabrication of a massive plug (250 m3) also called "con...

Cement-based materials would be commonly used for nuclear waste management and, particularly for geological disposal vaults as well as containers in France. Under service conditions, the structures would be subjected to simulta-neous drying and carbonation. Carbonation relates to the reaction between CO2 and the hydrated cement phases (mainly portl...

Simulations of atmospheric carbonation of Intermediate-Level Long-lived radioactive Waste (ILLW) concrete packages were conducted to evaluate their possible chemical degradations. Two-phase liquid water-air flow is combined with gas component diffusion processes leading to a progressive drying of the concrete.Complete drying of the 11 cm thick wast...

Within the context of long-lived intermediate level radioactive waste geological disposal, reinforced concrete would be used. In service life conditions, the concrete structures would be subjected to drying and carbonation. Carbonation relates to the reaction between carbon dioxide (CO2) and the main hydrates of the cement paste (portlandite and C-...

This article illustrates a contribution of the CEA Laboratory of Concrete and Clay Behavior ("LECBA") for the assessment and modeling of the Long-Term behavior of cementitious and clayey materials in the context of nuclear ILW (Intermediate Level Waste) management. In particular, we aim at presenting two main topics that are studied at the Lab. The...

In the framework of the study of a new concept for the geological disposal of high level radioactive waste in Belgium, a project of a supercontainer has been considered and studied. It is composed of a cylindrical concrete buffer containing two radioactive waste canisters to be inserted within an underground gallery. The main goal of this study is...

One of the main objectives of the APPLET project was to quantify the variability of concrete properties to allow for a probabilistic performance-based approach regarding the service lifetime prediction of concrete structures. The characterization of concrete variability was the subject of an experimental program which included a significant number...

Water transport is a key issue for concrete structures durability; the most important parameter may be the intrinsic permeability to water. It is usually estimated through inverse analysis on the basis of the experimental weight loss of concrete samples in a controlled environment. By doing so, Mualem’s model together with van Genuchten’s equation...

We studied the feasibility of a concrete package for radioactive waste management in a joint program involving Andra (the French agency for radioactive waste management) and CEA (the French atomic energy commission). The package's long-term durability and radionuclides' containment were the major concerns. The presence of junctions between the pref...

This study proposes two models for accelerated leaching in ammonium nitrate under variable temperature. The first approach assumes a thermoactivated linear relationship between degradation and the square root of time. The second approach introduces, within a phenomenological model, the thermoactivation of diffusion and hydrates solubility. These tw...

We have focused on the test conditions influence on accelerated degradation of cementitious materials using ammonium nitrate. PH-buffering and renewal of the leaching solution were studied. PH-buffering appeared not to be very important when the renewal pH remains under eight. Renewal appeared to be the most influential feature. Its absence leads t...

In this study all the data needed to describe water transport (drying) within an existing concrete structure were characterized using a simple drying experiment. The properties (desorption isotherm, porosity and the unsaturated water transport properties namely, diffusivity and permeability) were evaluated by post-processing the weight loss data. O...

Concrete deterioration results in different damage extents, from cracking to concrete spalling, from losses of reinforcement cross-sections to bond losses. A relevant prediction of this performance is the basis for a successful management of the concrete structures. Conversely, the large amount of uncertainties related to parameters and models requ...

Corrosion is the major cause of reinforced concrete structures degradation: the pressure generated by oxides formation together with section loss can eventually lead to cracking and the fall in the structure bearing capacity and then jeopardize its service life. The first method for the corrosion state characterisation of concrete structures is to...

Le programme de recherche APPLET « Durée de vie des ouvrages : Approche Prédictive PerformantielLE et probabilisTe » (cf. communication de Ch. Cremona sur le programme), a été financé par l'Agence Nationale de la Recherche en 2007 pour une durée de 3 ans et bénéficie d'une labellisation du pôle de compétitivité ADVANCITY. Son consortium est composé...

In the framework of the radioactive waste management in France, interim storage concrete structures should be submitted to temperatures up to 80 °C and subsequent desiccation. The impact of temperature on the sorption properties of concretes has been poorly studied and results are scarce. An experimental campaign was thus carried out to characteriz...

In the field of radioactive waste management the concrete structures are expected to undergo significant heating due to the waste thermal power and significant drying (in the French design, the temperature is not expected to exceed 80 °C). The durability assessment of such structures thus requires the knowledge of the evolution of the water vapour...

This article presents a new model which aims at predicting the expansion induced by Alkali Silica Reaction (ASR) and describing the chemical evolution of affected concretes. It is based on the description of the transport and reaction of alkalis and calcium ions within a Relative Elementary Volume (REV). It takes into account the influence of the r...

The ONDRAF/NIRAS agency for radioactive waste and enriched fissile materials is in charge of the management of the radioactive wastes in Belgium. In the framework of the study of a new concept for the disposal of high level wastes, a project of a supercontainer has been considered and studied. The main goal of this study was to estimate the Thermo-...

Alkali-silica reaction (ASR) is a concrete pathology due to chemical reactions involving reactive silica from reactive aggregates and the inner solution of concrete. Main effects are swelling, cracking, and reduction in the mechanical properties of affected concretes. Water is very important for ASR; the more available water, the more expansion and...

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 aggregat...

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 determi...

Rapporteurs : Franz-Josef Ulm et Erick Ringot President du jury : Karen Scrivener Jury : Francois Toutlemonde, Genevieve Thevenin-Foray, Eric Bourdarot, Bruno Capra et Alain Sellier

La réaction alcali-silice est une pathologie des bétons qui se caractérise par une réaction chimique entre la silice amorphe ou mal cristallisée contenue dans les granulats réactifs et certains ions de la solution interstitielle. Les conséquences macroscopiques de la réaction sont le gonflement de ouvrages atteints qui entraîne de la fissuration et...