Effect of curing temperatures on the alkali activation of crystalline continuous casting stainless steel slag

• Continuous casting slag shows hardening with alkali silicates under steam curing.
• Strength improvement is initially gradual but steeper at higher temperatures.
• Short term strength is dependent on alkali cations.
• Porosity of the mortars is more affected by alkali cations than curing temperature.
• Bonding between aggregate and matrix is majorly affected by curing temperature.

The binding properties of continuous casting stainless steel slag were studied when activated by a combination of Na silicate and 5 M NaOH as well as K silicate and 5 M KOH at steam curing temperatures of 60, 70, 80, 90, 100 and 110 °C. The slag mortars developed moderate compressive strength (∼5 MPa) at 60 °C which initially increased moderately and then steeply (>30 MPa) at higher curing temperatures. The porosity of K activated mortars was lower than for Na activated mortars. Thermal and ATR-FTIR analysis showed the formation of C–S–H type of reaction products for both activators at all temperatures, while the formation of brucite was promoted at higher curing temperatures. A much denser hydrated matrix with a better bonding with aggregates was formed at higher curing temperatures. Heavy metal leaching from the slag was dependent on its type and curing temperature of samples.