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The change of silica tetrahedron in cement-silica fume blends hydration is critical for blended cement application.29Si solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) investigations on the change of silica tetrahedron, which were Portland cement hydration,silica fume in simulated hydration and cement-silica fume blends hydration, were characterized and compared in this paper.The experimental results revealed that the amorphous silica tetrahedron structure in silica fume changed into Q1 and Q2 silica tetrahedrons, the same as silica-oxide structure of cohesive gel in the hydration of Portland cement.The coexistence of Q1 and Q2 silica tetrahedron in hydration product was beneficial to the strength increase of blend paste with silica fume.The amount of Q2 silica tetrahedron in cement-silica fume blends was higher than that in Portland cement.The pozzolanic reaction of silica fume accelerated the course of the silica tetrahedron in blended paste turning into the stable state of Q2 silica tetrahedron and existing principally in blended paste.That is reason that the physical properties of cement-silica fume blends are better than those of Portland cement.