Abstract: Since amorphous C12A7 has higher, metastable state chemical energy, it has a faster rate of hydration.The setting and hardening of OPC can be accelerated just by the existence of small amounts of C12A7.The effect of amorphous C12A7 mineral on OPC properties were studied.The effects of 0-2.0 ratio of C12A7/SO3 on OPC macroscopic properties including setting time, fluidity and early compressive strength were discussed.At the same time, the optimal C12A7/SO3 ratio carried out preferably by gray related degree method, and then its microscopic mechanism was analyzed by hydration heat, XRD, SEM.The results show that: adding amorphous C12A7 can accelerate OPC coagulated and reduce its fluidity.The effect of different ratio of C12A7/SO3 on OPC mortar early strength is different respectively, which can significantly optimized OPC earlier performance when C12A7/SO3 is 0.4.C12A7 can accelerate the hydrolysis of C3S, C2S in OPC.Reaction of hydration products including ettringite, C-S-H gel and calcium hydroxide cemente together, which play an important role in early hardening of OPC.

Key words: amorphous C12A7;cement;early property;microscopic mechanism