Abstract: The effects of fly ash, cement, compound activator and organosilicon waterproofing agent on the water resistance of flue gas desulphurization ( FGD ) building gypsum were studied .The research results show that there is no great improvement on the water resistance of FGD building gypsum when fly ash and cement are added to the system respectively .However , the flexural strength of the sample is above 6 MPa, the compressive strength is above 22 MPa and the flexural softening coefficient is above 0. 6 when fly ash , cements and compound activator are added simultaneously to FGD building gypsum system .Furthermore , the organosilicon waterproofing agent is added to the mixture system of fly ash , cements , compound activator and FGD building gypsum , the flexural softening coefficient of the sample is 0.756 and the compressive softening coefficient is 0.791 with add 0.8%waterproof agent , which are 64. 3%and 108.1%higher than that of pure FGD building gypsum , respectively, Water absorption rate is only 3.7%.It is indicated that the addition of self-made waterproof agent can significantly improve the properties of PEG building gypsum .

Key words: FGD building gypsum;cementing material;water resistance property