The effect of combined additions of silica fume, calcium sulphoaluminate, and gypsum on the hydration and strength development of Ca₂SiO₄

The strength development and hydration of β- and γ-C₂S mixes in the presence of silica fume, calcium sulphoaluminate and gypsum is strongly accelerated due to ettringite and C—S—H formation. Calcium sulphoaluminate contributes to strength only when conditions are modified to maximize the formation of ettringite. Therefore an addition of free CaO is needed in samples with low β-C₂S content. Strength in samples without C₄A₃S is lower because it depends on C—S—H formation. γ-C₂S hydration is neglibible compared with β-C₂S hydration, remaining unreacted even after more than one year in water.