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Dune sand is a very abundant material in south of Algeria. Its high silica content gives a partial pozzolanic reactivity due to its crystalline state. This paper investigates the evolution of cement hydration based on a binary addition particularly the reactivity of dune sand finely ground in the presence of an amorphous addition: silica fume or blast furnace slag. Thus, four combinations of binary additions by substitution have been chosen. The X-ray diffraction analyses performed on cement pastes containing additions have shown the importance of the mineralogy and silica content of additions on their pozzolanic reactivity. Dune sand becomes reactive at long term, especially when associated up to 10% of amorphous addition (blast furnace slag or silica fume). It results an increasing in mechanical strength of Ultra High Performance Concrete (UHPC) and an improvement of the microstructure

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