Abstract: In order to study the influence of gypsum and silica fume on the early compressive strength of portland cementing material, we test the compressive strength of cement with different content of gypsum and silica fume at 4 h, 1 d and 28 d respectively. The microstructure characteristics of hydration products were analyzed by X-ray diffraction and scanning electron microscope. In a certain range, research shows that the compressive strength of cementing material increases with the content of gypsum increases, the compressive strength reaches peak when the content is 0 . 75%, and compressive strength reached 5 . 8 MPa and 63. 4 MPa at 4 h and 1 d. Silica fume increased from 0% to 15%, the compressive strength of cementing material increased by the content went up. The microstructure characteristics of the hardened cement paste shows that in, a certain range of gypsum to brought the amount of AFt in the system increased, the silica made the C-S-H get increased in the system,and unhydrated silica filled the pore of system.

Key words: Portland cementing material;gypsum;silica fume;super early compressive strength