Hydration mechanism of composite binders containing blast furnace ferronickel slag at different curing temperatures

This study investigated hydration mechanism of composite binders containing blast furnace ferronickel slag at different curing temperatures. Different levels of cement replacement (15, 30, and 45% by mass) and curing temperatures (25 and 60 °C) were set. In addition to pure cement, a composite binder containing quartz with a particle size distribution similar to ferronickel slag was selected as the control sample. The results reveal that blast furnace ferronickel slag can show the pozzolanic reactivity at an early stage at room temperature despite low activity, and an early high curing temperature can improve the activity significantly. The influence of high curing temperature on the pozzolanic reaction is greater than the influence of high curing temperature on cement hydration at an early stage, and as a result, the Ca(OH)2 content in the cementitious system is lowered. However, the influence on the pozzolanic reaction is not obvious in the later stage. The high curing temperature does not change the type of hydration product but increases the content of the C–S–H gel, resulting in a significantly higher Ca–Si ratio and a slightly lower Al–Si ratio. In addition, the high curing temperature improves the early compressive strength of the concrete containing blast furnace ferronickel slag and reduces later compressive strength. A suitable dosage of blast furnace ferronickel slag may improve the resistance to chloride ion penetration of concrete at a high curing temperature.