Philippe Turcry

Evaluation of plastic shrinkage cracking of self-consolidating concrete

Self-consolidating concrete (SCC) is a fluid concrete, cast without vibration, that has a self-leveling ability that makes it appropriate for flat structures such as slabs or industrial floors. This article reports on a study that evaluated plastic shrinkage cracking of SCC. The authors compared five SCC mixtures with compressive strengths ranging from 30 to 50 MPa to five ordinary concrete (OC) mixtures. Free and restrained plastic shrinkage tests were performed in different drying conditions. When the evaporation rate is moderate (drying at 20 deg C and a relative humidity of 50%), plastic shrinkage occurs before and during setting. When the evaporation rate is high (windy condition), plastic shrinkage occurs only in the plastic state, that is, before setting. In the presence of wind, SCC and OC mixtures have almost the same plastic shrinkage and restrained shrinkage tests reveal that cracks of SCC tend to be less wide than cracks of OC. However, when the evaporation rate is low, SCC mixtures exhibit a higher plastic shrinkage than OC mixtures, due to their lack of bleeding. The authors conclude by recommending curing in order to protect SCC against evaporation at the fresh state.

Assessment of the variability of moisture transfer properties of High Performance Concrete from a multi-stage drying experiment

This article aims to assess the characterisation of the water vapour desorption process and its variability under site conditions. It presents a probabilistic approach allowing the assessment of the distribution laws for the water vapour desorption isotherms (WVDI) and the moisture diffusion coefficient. These two parameters were evaluated from multistage drying experiment. For each stage, the analysis of the equilibrium state allows the determination of WVDI whereas the analysis of the desiccation kinetic makes possible the evaluation of the moisture diffusion coefficient. In order to have a representative variability, the study was carried out on two different High Performance Concretes (HPC) during a large-scale construction: overall, more than 300 specimens were tested. Results indicate that Gaussian distribution can be used for modelling the statistical variability of desorption isotherm while log-normal distribution is more appropriate for describing the variability of moisture diffusion coefficient. Furthermore, whatever the concrete, the coefficient of variation on the water content at equilibrium remain very similar. Cet article a pour but la caractérisation du processus de désorption de la vapeur d’eau et de sa variabilité dans des conditions in-situ. Il présente une approche probabiliste permettant l’évaluation des lois de distribution des Isothermes de Désorption de la Vapeur d’Eau (IDVE) ainsi que celles des coefficients de diffusion d’humidité. Ces deux paramètres ont été évalués expérimentalement à partir d’essais de séchage par palier réalisés sur des bétons à haute performance (BHP), confectionnés in-situ. Pour chaque palier de séchage, l’exploitation des états d’équilibres hydriques a permis la détermination de l’IDVE. De plus, l’analyse des cinétiques de transfert a permis l’évaluation du coefficient de diffusion d’humidité. La campagne expérimentale a été réalisée sur plus de 300 échantillons. Les résultats obtenus ont révélés que la variabilité des isothermes de désorption peuvent être modélisés par une distribution Gaussienne tandis qu’une distribution de type log-normale s’avère plus appropriée pour décrire la variabilité du coefficient de diffusion d’humidité. En outre, quel que soit le béton testé, les coefficients de variation de la teneur en eau pour les différents états d’équilibre hydrique demeurent proches.

Numerical study of the influence of drying on properties governing the carbonation mechanism of concretes with low clinker content

This paper presents a numerical study of the coupling between cement hydration and drying of concretes with high amount of fly ash or blast-furnace slag and concretes with Portland cement or blended cements. The study, conducted with the MLS by FEMMASSE® code, aims at assessing the influence of drying on concrete properties governing carbonation kinetics, i.e. porosity, Portlandite content and liquid water saturation degree. These properties were found not uniform according to the depth within the concrete material. In the cover zone, high substitution concrete should have a higher carbonation risk than Portland cement concrete because of the slow hydration kinetics combined with the suspending effects of drying on hydration. Therefore, high substitution concrete should require a longer period of curing than Portland cement-based concretes.

Comportement mécanique de poutres attaquées par la corrosion : Utilisation du code de calcul Eficos

ABSTRACT The aim of this study is to predict the mechanical behaviour of beams which were in sea water for 40 years. Mechanical experimentations were carried out after inspection of beams: loading in four-point bending and loading in direct tension. The mechanical behaviour of the beams is modelled before and after being corroded, with the software Eficos. The steel corrosion is taken into account only by a reduction in steel cross section because steels have no anchorage. A good correlation is obtained between simulations and experimental results for bending in the case of reinforced concrete.