A low-carbon cement based on silicomanganese slag and granulated blast furnace slag: Hydration process, microstructure, mechanical properties and leaching risks

The calcium content of silicomanganese slag is only about 50 % of that in granulated blast furnace slag but the manganese content is high (>10 wt%), which limits the wide application of silicomanganese slag in cementitious materials. The present study provides a low-carbon cementitious material with an above-average silicomanganese slag content, which provides a new method for the recycling of silicomanganese slag and other solid wastes. The mechanical properties, hydration mechanisms, and pore structures of low-carbon cementitious materials with different silicomanganese slag and granulated blast furnace slag ratios were investigated using carbide slag as alkali-activator and flue gas desulfurization gypsum as sulfate-activator. The feasibility of silicomanganese slag as a significant replacement for granulated blast furnace slag in cementitious materials was explored, and the risk of manganese leaching was assessed. Silicomanganese slag has slower hydration rate in the early stage, but the reaction accelerates in a later stage and the gap with granulated blast furnace slag decreases. The 3, 7, and 28-d compressive strengths of mortars consisting of 40 % silicomanganese slag, 40 % granulated blast furnace slag, 12 % flue gas desulfurization gypsum, and 8 % carbide slag reached 28.7, 41.2, and 49.9 MPa, respectively. When the silicomanganese slag content is 80 %, the leaching toxicity test results showed <= 0.1 mg/L, and jouravskite was present in the hydration products, which indicated a low risk of manganese leaching in normal service environments.