Research On Water Resistance Of FGD Gypsum-based Composite Materials

Flue gas desulfurization gypsum mainly come from coal-fired power plant and China’s numerous coal-fired power plants produce large amounts of flue gas desulfurization gypsum every year. FGD gypsum which mainly used in the construction industry is an excellent cementitious material, but the application of FGD is large limitted because of it’s poor water resistance. Improving the water resistance and taking into account of the strength at the same time can greatly expand the applications of the FGD gypsum products.This paper mainly studies the measures to improve the water resistance of desulfurization gypsum. The research methods are as follow:Compacting the structure of FGD gypsum products can improve the strengh and water resistance by reducing the mixing water consumption; Introducing waterproof material into gypsum products. Waterproof admixture can form a dense protective film on the surface of the gypsum particles which change the affinity of the building plaster and water, thus the gypsum products can not be destruction by ingressing of the water; Introduct hydraulic skeleton into gypsum products can effectively resist the damage of the water, strong water resistance comes from cementitious products which is insoluble in water; The article also discussed water resistance of free calcined gypsum-based materials. The results show that:(1)Adding polycarboxylate superplasticizer and aliphatic superplasticizer can effectively reduce the mixing water of the desulfurization building gypsum, thereby improving its water resistance. Fluidity loss of desulfurization gypsum can be effectively delay by complex doped retarde.The incorporation of these two superplasticizer can reduce water absorption and increase dry strength of gypsum products. Polycarboxylate superplasticizer does well in reducing the water absorption and aliphatic superplasticizer exhibit better in improveing the strength of gypsum products under equal dosage. The softening coefficient of gypsum products increases in the beginning and then decreases slightly as superplasticizer dosage increase. When the superplasticizer content is1.6%, the softening coefficient reach to a maximum value of0.75.(2)EVA and PVA can both improves the water resistance of gypsum products to a certain extend. With the increase in the dosage of the two waterproof admixture, the water absorption of the gypsum products are rapidly reduced in the beginning and then decreased to flatten, dry strength increase gradually and then reduce significantly, and softening coefficient are rise rapidly at first and then stabilized. When the dosage of EVA and PVA are4%, the softening coefficien of the gypsum products reach to a maximum value of0.80and0.83.(3)The water absorption of the gypsum products reduces significantly,dry strength increases gradually and softening coefficient increase at first and then stabilize when quicklime or cement are added in the gypsum-fly ash system or the gypsum-slag system. Gypsum-slag system exhibit higher strength and better water resistance than gypsum-fly ash system when added the same dosage of cement or lime. A large amount of the hydraulic product are generate in the case of plaster exist as the activity of the slag is prefferably excited in the existing conditions of the cement or lime. Thermal analysis and XRD analysis show that there are a lot of gypsum as well as more C-S-H and a small amount of AFt.(4)Free calcined desulfurization gypsum composite materials exhibit high strength when3%cement are added, the maximum compressive strength can reach to20.3MPa, but strength reduces with more cement. Free calcined desulfurization gypsum composite strength exhibit higher strength in the curing of the hot and humid than in the curing of water. Considering that this material are curried in water-saturated environment, the materials can be used in amoist environment and maintain a certain strength.