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Etude de l'accélération des ciments à haute teneur en laitier de haut-fourneaux par du chlorure de calcium

Abstract : Blast furnace slags are a co-product of the metallurgical industry, used in composite cements (CEM II & III) as a partial substitution for Portland clinker and recognized in particular for their advantages in terms of lowering the heat of hydration, increased durability performance and reduced carbon footprint of concrete. Although achieving ultimate mechanical performance comparable to or better than Portland cement (CEM I), binders offering high levels of slag see the development of their mechanical strength greatly slowed down. This phenomenon is explained by a lower reactivity of the slag which requires "activation" conditions to react properly. There are various additives that accelerate the hardening of cements, among which calcium chloride shows the best performance. The effects of calcium chloride are particularly important during the first days of hydration. However, their use is strongly regulated because of the corrosive effect of chlorine on steels of reinforced concrete. The objectives of the thesis are to study the mechanisms of action of calcium chloride on cement-slag binders during the first days of hydration. A panel of experimental techniques has been used to specifically identify the action of chlorides on slag and cement. Coupled results from XRD-NMR SEM experiments show that calcium chloride causes an accelerated precipitation of portlandite and ettringite, resulting from the increase in the reaction rate of clinker. The start of the slag reaction takes place after about 12 hours, and is not impacted by the calcium chloride. On the other hand, the reaction rate of the slag increases in the presence of the accelerator. The rapid, significant and exclusive formation of Friedel salts in the presence of chloride is observed, replacing sulphated and / or carbonated AFm. Increasing the reaction rate of the anhydrous phases results in the precipitation of additional C-S-H. This formation of Friedel salts and C-S-H causes a faster filling of the porosity and the increase of the mechanical performances.
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  • HAL Id : tel-03324584, version 1

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Laurent Steger. Etude de l'accélération des ciments à haute teneur en laitier de haut-fourneaux par du chlorure de calcium. Génie civil. Université Paul Sabatier - Toulouse III, 2019. Français. ⟨NNT : 2019TOU30333⟩. ⟨tel-03324584⟩

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