Synergistic Effect of Alkali-activation and Carbonation on Carbonated Steel Slag Bricks

The effect of alkali-activation with carbonation on the properties of carbonated steel slag bricks was investigated. The results show that steel slag is a suitable starting material for carbonated bricks due to its CO2 sequestration. Na2CO3 as a feasible activator shows a better improvement according to the strength growth and CO2 sequestration. The strength of carbonated bricks containing Na2CO3 increases with the increase of steel slag volume, but CO2 sequestration gradully decreases due to the more compact matrix in which the steel slag volume is 1 800 kg/m3. The bricks made of steel slag powder with a greater fineness have a greater CO2 sequestration, but the increment of CO2 sequestration of the bricks made of ultra-fine powder with a fineness of more than 440 m2/kg becomes weak. A high volume of aggreagte causes a greater sthrength, and the change in CO2 sequestration does not appear. A suitable dosage of water in steel slag (i.e., 7%-13%) can favor carbonating, but the excessive water (i.e. 11%-13%) leads to a decrease of CO2 sequestration. The solely accelerated carbonation leads the strength of bircks with 7% water to increase by more than 20.0 MPa. Furher more, the incorporation of 0.75% Na2CO3 results in a further strength gain of more than 10.0 MPa due to the synergetic effect of carbonation and alkali-activation. The optimized mixture of bricks consists of 1 640 kg/m3 of steel slag with a specific surface area of 440 m2/kg, 328 kg/m3 of aggreagte (20%, mass ratio of aggregate to steel slag, the same below), 115 kg/m3 of water (i.e., 7%) and 13.12 kg/m3 of Na2CO3 (i.e., 0.75%). The strength of optimized carbonated bricks with CO2 sequestration of 9.15% is 39.2 MPa. The more calcite foramtion and its stronger filling effect are the main reason for the strength gain of carbonated bricks activated by Na2CO3. © 2019, Editorial Department of Journal of the Chinese Ceramic Society. All right reserved.