Development of an MgO-based binder for stabilizing fine sediments and storing CO2.

An MgO-based binder was developed that could stabilize fine dredged sediments for reuse and store CO2. Initially, a binder consisting of fly ash (FA) and blast furnace slag (BFS) was developed by using alkaline activators such as KOH, NaOH, and lime. The FA0.4-BFS0.6 binder (mixed at a FA-to-BFS weight ratio of 4:6) showed the highest compressive strength of 10.7 MPa among FA/BFS binders when 5 M KOH was used. When lime (L) was tested as an alkaline activator, the strength was comparable with those obtained when KOH or NaOH was used. The L0.1-(FA0.4BFS0.6)0.9 binder (10 % lime mixed with the FA/BFS binder) showed the highest strength of 11.0 MPa. Finally, by amending this L0.1-(FA0.4BFS0.6)0.9 binder with MgO, a novel MgO-based binder (MgO0.5-(L0.1-(FA0.4BFS0.6)0.9) 0.5) was developed, which demonstrated the 28th day strength of 11.9 MPa. The MgO-based binder was successfully applied to stabilize a fine sediment to yield a compressive strength of 4.78 MPa in 365 days, which was higher than that obtained by the Portland cement (PC) system (3.22 MPa). Carbon dioxide sequestration was evidenced by three observations: (1) the decrease in pH of the treated sediment from 12.2 to 11.0; (2) the progress of the carbonation front inward the treated sediment; and (3) the presence of magnesium carbonates. The thermogravimetric analysis (TGA) results showed that 67.2 kg of CO2 per ton of the treated sediment could be stored under the atmospheric condition during 1 year.