Understanding the multiple actions of phosphoric acid-modified steel slag powder on early-age hydration of cement

The retardation of the early-age hydration of cement by steel slag powder severely restricts its use in cementitious materials. This paper reports on the modification of steel slag powder with phosphoric acid, which is found to alleviate its inhibition of cement hydration. Comprehensive investigations of solid phase assemblage and elements dissolving behavior in cement pastes reveal that multiple actions combine to determine the effect of phosphoric acid-modified steel slag powder on cement hydration. By using an appropriate amount of phosphoric acid for modification, a noteworthy reduction in C12A7 content and a significant increase in the specific surface area of steel slag powder can be achieved. This consequently enhances the reactivity of steel slag powder and diminishes its negative inhibitory effect on hydration. However, excessive use of phosphoric acid exacerbates the delayed effect of calcium phosphate on mineral dissolution, so that the inhibitory effect of steel slag powder on cement hydration cannot be alleviated.