Sulfate resistance of mortar containing simulated FGD waste

This paper is part of a wide-ranging research project on the optimum use of waste from the dry and semi-dry flue gas desulfurisation (FGD) processes in concrete. It reports on the sulfate resistance of mortars containing a typical simulated desulfurised waste (SDW). Two binder systems were investigated: (a) cement and SDW with replacement levels of 0 to 70% and (b) cement (10%), slag (20–90%) and SDW. The influence of SDW content (0–70%) on sulfate resistance was evaluated. Specimens were exposed to 2·2% sodium sulfate solution and 2·44% magnesium sulfate solution. The results showed that replacing cement with increasing levels of SDW improved the sulfate resistance in each sulfate solution. This was attributed to the dilution of C3A and CH due to the reduction in cement, pore refinement and the formation of ettringite during early periods of hydration. Mortars containing cement, slag and SDW exhibited superior sulfate resistance in sodium sulfate solution. When immersed in magnesium sulfate solution, they underwent some deterioration due to the reaction with the C–S–H, CH and C–A–H phases. At SDW contents above 20%, resistance to magnesium sulfate was satisfactory.