Microstructure Change of Air Quenched Steel Slag and Its Hydraulic Activity

Microstructure of air quenched steel slag was observed and cement mortars based on the slag was prepared. The type of mineral phases in the slag remains unchanged with increasing time. Within 20 days, some small dicalcium silicate grains in the slag disappeared, and some dicalcium silicate grains grew larger and amalgamated together with neighboring grains. After 20 days, dicalcium silicate grains have no obvious changes. Size distribution of dicalcium silicate at different ages closely approaches a lognormal distribution and the curve shifts to the right with increasing time, indicating that grain size became larger. Compressive and bending strength of cement mortars based on air quenched steel slag at different ages decrease with increasing age of the slag within 20 days, which indicates that the hydraulic activity of air quenched steel slag decreases with time. After 20 days, the slag was stable and the hydraulic activity achieved to the lowest.