Investigation of the effects of alkali activation and CO2curing on BOF steel slag

The present work reports the results obtained by coupling alkali activation and CO2 curing as a treatment for BOF slag, with the aim of improving the hydraulic reactivity of the residue while also exploiting its potential as carbon sink. The slag was mixed with two different solutions: NaOH (2M)+Na2SiO3 (50:50 by wt.) and NaOH (4M)+Na2CO3 (2M) (75:25 % by wt.) and then cured for 3, 7 and 28 days, in either a humidity chamber (RH=90% and T=20 °C) or in a carbonation chamber (RH=75%, CO2=5%) at both environmental and enhanced conditions (T=50 °C). TGA results, confirmed by XRD analysis, showed an increasing loss in weight corresponding to the decomposition of carbonates by increasing the curing time for both activators and curing conditions, while a significant occurrence of gaylussite at early curing times and low curing temperature was observed, mainly for the sodium carbonate solution. The highest CO2 uptake (6% wt. slag) was achieved for the BOF slag samples mixed with the sodium hydroxide/sodium carbonate solution after 28 days of curing in the carbonation chamber, regardless of the temperature adopted. The maximum value of the compressive strength (2 MPa) was obtained after 7 days of curing in the carbonation chamber at 50 °C for mortar samples prepared with sodium silicate.