The incorporation of waste in concrete manufacture may provide a satisfactory solution to the problems posed by waste management. The building sector uses large quantities of natural materials; hence its capacity to recycle and upgrade waste is considerable. Certain industrial by-products have been used for a number of years as cement or concrete components (fly ash, silica fume, etc.). Other waste products may also be recycled and upgraded in concretes. However, the new material thus formed must be usable as a building material and, in particular, have the necessary performance characteristics (workability, mechanical strength, etc.) to satisfy the specifications determined by its applications. In addition, it should be inoffensive with regards to health and the environment. Finally, the incorporation of the waste should not impair the concrete's durability. Traditional assessment methods must therefore be adapted to evaluate these new materials.
This study contributes to the development of a methodology for assessing concrete manufactured from waste. The methodology is based on the study of mortar containing experimental waste: Municipal Solid Waste Incineration fly ash (MSWI fly ash) [1, 2]. The ash is considered as experimental waste because of, in particular, its high content of soluble salts and heavy metals. We stress the fact that the present research work does not aim to study a process or a formulation enabling the incorporation of this waste in concrete.
The durability and the environmental impact of concrete are closely connected to its transport properties, which control the kinetics of the penetration of water and aggressive agents into concrete. The movement of chemical species within the material and the leaching-out of certain chemicals are also closely linked to the concrete's diffusivity. However, the transport (properties of concrete are likely to develop considerably as the material ages (carbonation, leaching, etc.). The study of the development of the microstructure of concrete containing waste is therefore very important in predicting the long-term behavior of these materials.
To study the long-term development of the microstructure of concrete containing waste during the leaching process, we applied the CEMHYD3D hydration model [3], originally developed by Bentz and Garboczi [4], to cement pastes containing MSWI fly ash. In this article, we present the experimental research carried out to determine the model's input data. The second part of the study, to be published in a future article, will present the results of the model.
The physical, chemical and mineralogical characteristics of the MSWI fly ash were first analysed to incorporate it into the hydration model. Hydrates formed in pure cement pastes and pastes containing ash were then analysed to include the ash/cement interactions in the model. Finally, the performance characteristics of mortars containing increasing levels of MSWI fly ash were studied to identify the short and middle-term influence of the ash on mortars' properties.