Preliminary investigation on the pozzolanic activity of superfine steel slag

• Superfine steel slag with different particle sizes were prepared.
• The chemical and mineral compositions of the steel slag were analyzed.
• The activity index of superfine steel slag is much higher than ordinary steel slag.
• Too much superfine steel slag is disadvantage to the strength of cement mortar.
• The cement paste with superfine steel slag has much more hydration products.

In this research, superfine steel slag with different particle sizes were prepared by a superheated steam powdered jet mill, then the pozzolanic activity of the superfine steel slag was investigated. The results show that the content of f-CaO decreases when the particle size of steel slag is decreased. The requirement of normal consistency for water, setting time, and soundness of the cement paste with the superfine steel slag all remain within the acceptable ranges of the national standard. A decrease in the particle size of superfine steel slag can accelerate the hydration reaction of blended cement and results in higher mortar strength. The activity index of superfine steel slag (D50 = 2.52 μm) can reach up to 95.0% which is much higher than that of ordinary steel slag powder (D50 = 13.3 μm). For blended cement with 10% weight ratio of superfine steel slag (D50 = 5.10 μm) as a replacement, cement mortar exhibits higher compressive strength at 28 days than that of pure cement mortar. While the strength of cement mortar is gradually decreased when the replacement weight ratio of superfine steel slag is above 10%. Microstructure analysis confirms that there are more hydration products yielded in cement paste with superfine steel slag than that of ordinary steel slag powder, which is consistent with the result of mechanical experiments.