Abstract: The effect of different content of amorphous C12 A7/CaSO4 · 2H2 O system on the early properties of setting time, fluidity and compressive strength of OPC was to investigate. Hydration products were tested by X-ray diffraction ( XRD ) and Scanning electron microscope ( SEM ) , and hydration process was analyzed by calorimetric method. The results show that C12 A7/CaSO4 ·2H2 O system used 5% of unit weight of cement, the mass ratio of C12 A7 and CaSO4 ·2H2 O was 1. 0 to 1. 0, the system accelerated the hydration of C3 S and C2 S, the hydration product C-S-H gel intertwined overlap to form the network structure which resulted the quick setting of cement paste, it also formed a large amount of acicular ettringite, the structure of hydration products was more and more compact, because of the ettringite filled with C-S-H gel each other, it improved the early strength of cement paste.

Key words: amorphous C12 A7;ettringite;early compressive strength;hydration