Influence of the pozzolanic reactivity of the Blast Furnace Slag (BFS) and metakaolin on mortars

Abstract The objectives of this study is to evaluate the pozzolanic reactivity of mortars with two mineral admixtures (Metakaolin and BFS) in substitution of cement. The rate of substitution is fixed after optimization of the mechanical results. Metakaolin and the BFS from blast furnaces have been used with 10% and 40% respectively to the replacement of the cement. At long time, the use of two admixtures provides better results to those of the mortar of reference at early age, The mortar containing metakaolin provides results better than the mortar of reference, while mortar containing BFS gives inferior results up to 70% of the referential mortar. Metakaolin by its important specific surface area and its reactivity improves the mechanical behavior at early ages. However, the BFS reacts very late. In order to improve the mechanical results at early and long time, a new mortar were casted with 10% of MK and 40% of BFS in substitution of the cement. Isothermal calorimetry and compressive strength tests were performed. Hydration phenomena were also analyzed.