Micheline Moranville

Durability of reactive powder composites: influence of silica fume on the leaching properties of very low water/binder pastes

Abstract Reactive Powder Composites are new cement-based materials which could be used for the storage of nuclear wastes thanks to their excellent microstructural properties. This paper studies their durability when submitted in the laboratory to a water leaching attack. In order to understand the behaviour of the hydrates (CSH), the study was carried out on a pure cement paste and on a cement + silica fume paste. The beneficial effect of silica fume is demonstrated from considerations on the calcium leaching, from XRD analysis, from SEM observations and from the tritium diffusion and pore distribution analysis. It was found that the leaching greatly affects the microstructure, especially that of the anhydrous cement grains remaining in the paste.

Modelling the leaching kinetics of cement-based materials––influence of materials and environment

The leaching of cement-based materials in aggressive water is studied according to several protocols of accelerated or non-accelerated tests. The paper analyses international experimental published data on leaching concerned with several parameters, like material parameters as water-to-binder ratio and silica fume content, and environmental parameters, like pH and temperature. Then, a simplified model based on this analysis is developed to predict the kinetics of leaching. This model assumes that the rate of leaching follows a square root of time. Each parameter is introduced as a weight function. Particularly, the paper introduces the coupling between the built database and the model.

Microscopic observation of cracks in concrete — A new sample preparation technique using dye impregnation

Abstract A new technique to prepare concrete sections for microscopic examinations is briefly described. The procedure involves the impregnation of a concrete section with a colored dye diluted in an alcohol. After a short impregnation period during which the concrete is constantly kept humid, the section is polished under water. Contrary to most dye impregnation techniques, this method does not involve any drying of the sample. Observations of cracks using optical microscopy can therefore be made without concern about drying shrinkageinduced cracking. In addition to a detailed description of the preparation technique, various examples of the application of the method are given. The possibilities of using this dye-impregnation technique in combination with an image-analysis system are also discussed.

Séchage et retrait : Influence de la fissuration induite

ABSTRACT In this paper, we present a study on the drying of cement-based materials. Monitoring the weight loss of a concrete specimen in a controlled relative humidity room could be a way to determine the water permeability of concrete. However, we show that this method depends in a great extent to the used models. Two models for the desorption isotherm are used in order to show that the choice of the model has a great impact on the identified water permeability. Moreover, numerical simulations taking into account damage are performed in order to understand the effect of cracking on the identified water permeability.