Effects of sodium aluminate on fleeting semi-dry carbonation and properties of steel slag powders in low concentration CO2 atmosphere

Abstract

Accelerated carbonation suffers from the limitation of low efficiency when CO2 supply is inadequate. This study aims at proposing a carbonation accelerator of sodium aluminate (SA) to stimulate the reaction between steel slag and CO2. Additionally, a fleeting semi-dry carbonation is proposed and mixed gas with 20 vol% CO2 was used to simulate the CO2 concentration of flue gas. According to the MGC results, with only 0.07 wt% of SA added, steel slag obtained 3.55 wt% of CO2 uptake after 10 min carbonation under 20 vol% CO2 atmosphere, which is 36.02 % higher than that of the carbonated control steel slag. As a result of elevated carbonation efficiency, f-CaO (free calcium oxide) in SA incorporated steel slag (SA-SS) is decreased more substantially than that of the control steel slag after carbonation. According to autoclaving test, cement paste cast with carbonated SA-SS showed less expansion than the one cast with carbonated control steel slag. Mortar cast with carbonated SA-SS obtained a competitive compressive strength of 40.63 MPa at 28 d. SA plays the role as a pH buffer that slows down the alkalinity decrease during the fleeting carbonation and hence enables more CO2 to dissolve in water. With enhanced carbonation efficiency, CaCO3 particles in carbonated SA-SS are big cubes which is opposed to the small, shapeless grains in carbonated control steel slag.