La valorisation des poussières de four de cimenterie en vue de leur exploitation en tant que barrière environnementale requiert, entre autres, l'ajout de cendres volantes afin d'améliorer les différentes propriétés nécessaires à une meilleure mise en place et assurer leur efficacité à long terme. En mettant à profit différentes techniques expérimentales, une attention particulière est accordée au comportement physico-chimique de différentes poussières de four associées aux cendres volantes. Selon la nature des ajouts considérés, un comportement différent peut conditionner l'évolution des mélanges avec une incidence sur leur stabilité. En effet, cette étude a confirmé l'amélioration des propriétés physico-chimiques des poussières mises en interaction avec les cendres volantes riches en silices, et pauvres en chaux, ce qui laisse de bons augures quant à leur utilisation en tant que barrière environnementale. Par ailleurs, le suivi a permis une meilleure compréhension de certains mécanismes générés par les systèmes abordés. Ainsi, après hydratation et différentes transformations chimiques, des phases à caractère expansif tels que l'ettringite, le gypse, la syngénite et la portlandite, prennent naissance dans la pâte et conditionnent, par conséquent, le comportement des mélanges élaborés.Abstract: Enhancing the value of the cement kiln dust so as to use it as an environmental barrier requires, amongst other things, the addition of fly ashes in order to improve the different properties needed to insure a better placing and a long term efficiency. Taking advantage of different experimental techniques, particular attention was devoted to the physicochemical behaviour of different kiln dusts associated with the fly ashes. Depending on the nature of the added compound, a different behaviour may condition the evolution of the mixtures with an effect on their stability. Indeed, this study has confirmed the improvement of the physicochemical properties of the dusts interacting with the fly ashes rich in silica and poor in lime, which argues well for their use as an environmental barrier. Moreover, the follow up has led to a better understanding of certain mechanisms generated by the systems dealt with. Hence, after hydration and different chemical transformations, some expansive phases as the ettringite, gypsum, syngenite, and portlandite develop in the paste, and therefore condition the behaviour of the mixtures worked out.
Pyritic aggregates coming from sedimentary rocks may be subject to expansions when used in subbases, and, in certain cases, may then cause heaving or expansion of concrete slabs with consequences on the structures. This situation occurs in areas where the lack of prime aggregates requires the use of local materials. Swellings are observed and are basically related to the oxidation of sulphides such as pyrite, pyrrhotite, and chalcopyrite, which are present in aggregates. As a result of this oxidation, sulphuric acid is formed and reacts to produce gypsum, which is responsible for the increase of volume. This paper is a contribution to a better understanding of this topical phenomenon and also includes the procedure of characterization used for four aggregates to determine their expansive potential by using an experimental device developed at the laboratory. Different reactivity modes take place involving processes such as swelling and sulphate attack or even the combination of the two modes, which are corroborated by the intrinsic properties of the aggregates used in this study.Key words: subbase, aggregates, pyrite, oxidation, gypsum, swelling.
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