PROPERTIES AND ENVIRONMENTAL IMPACT OF CEMENTITIOUS MATERIALS PREPARED WITH FLUORGYPSUM AND STEEL SLAG

The industrial by-products of fluorgypsum (FG) and steel slag (SS) were recycled for the preparation of gypsum-based cementitious materials (GBCMs). Na₂SO₄ and KAl(SO₄) ₂ were applied to activate the hydration of FG and SS, respectively. The properties of the GBCM were investigated. The residual H2SO4 and soluble F in the FG poses a great threat to the environment. Hence, the environmental impacts of the GBCM were also studied. The results demonstrate that, with an increase in the SS content of the GBCM, the water requirement for normal consistency increases, the setting times are obviously prolonged, while the mechanical strength and the linear expansion rate are lower. Due to the hydration of SS and the formation of ettringite at a late hydration age, both the compressive strength and flexural strength for FG: SS=9:1 and FG: SS=8:2 are close to that of FG: SS=10:0 at 90 d. The water resistance of the GBCM paste is also improved by adding SS into the FG. Hence, considering the mechanical strength and water resistance, the SS content of the GBCM should not exceed 20%. The H2SO4 in the GBCM can be neutralised by SS. Furthermore a novel quick and effective method, through the precipitation of AlF₃, for the immobilisation of soluble F was proposed. Therefore, FG and SS can be recycled for the production of GBCM without bringing about an adverse environmental impact.