Accelerated carbonation – A potential approach to sequester CO2 in cement paste containing slag and reactive MgO

The cement industry and concrete producers are under pressure to reduce the carbon footprint and energy demands of cement-based construction materials. This study investigates the CO2 uptake of paste mixtures designed with general use (GU) Portland cement, ground granulated blast furnace slag (GGBFS) and reactive MgO as cement replacement due to exposure to an accelerated carbonation curing regime with 99.9% concentration of CO2. The CO2 uptake, carbonation mechanism, microstructure and microhardness of cement pastes are examined. Key outcomes revealed that: (i) samples exposed to accelerated carbonation curing exhibit a denser microstructure and higher microhardness in comparison to non-carbonated samples, (ii) irrespective of the presence of reactive MgO, CO2 uptake increases with age from 7 to 56 d, (iii) by 56 d, pastes containing 10% and 20% reactive MgO uptake similar amounts of CO2 in comparison to mixtures without reactive MgO, and (iv) pastes containing 40% reactive MgO uptake the least amount of CO2 however, exhibit the greatest microhardness and the lowest porosity.