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No abstract

CO2 accelerated concrete curing has been recently suggested as a carbon dioxide mitigation technology in which CO2 is reacted with cement and stored as a thermodynamically stable carbonate in concrete construction products. In this research, the rate and extent of CO2 uptake by concrete is assessed in a flow-through reactor. Carbonation efficiencies of 16−20% attained in a flow-through reactor was comparable to those obtained for static CO2 pressure chambers employed in previous studies for accelerated concrete curing. However, significantly less energy is required in a flow-through reactor compared to a CO2 pressure chamber. Intermittent carbonation experiments showed that the carbonation efficiency was limited in part by slow dissolution and/or diffusion of dissolved reactive components in the concrete matrix.

Accelerated curing of fresh concrete using CO 2 is a possible approach for value-added, high-volume usage products from waste CO 2 emitted from stationary sources. The extent of CO 2 uptake and the spatial distribution of the CaCO 3 (s) precipitates formed during accelerated carbonation curing of compacted, 4-h hydrated cement mortar (fresh concrete mixture with fine aggregates) samples were investigated in this study. The maximum carbonation efficiency achieved was 20% of the theoretical uptake. Microprobe imaging was used to analyze the composition of the compacted cement mortar microstructure and showed extensive filling of pores of diameters 4 μm and smaller, with CaCO 3 (s). The carbonation efficiency, however, reached 67% when an aqueous suspension of cement was carbonated in a completely mixed reactor, where interparticle pores do not exist and a higher surface area of cement particles is exposed to dissolved CO 2 . The theoretical efficiency was not achieved because all reactive cement surfaces were saturated with carbonation products, as indicated by equilibrium concentrations of dissolved calcium, silica, inorganic carbon, and pH. This study shows that both deposition of CaCO 3 (s), on reactive surfaces, and pore filling may regulate the extent of CO 2 uptake during accelerated carbonation curing of concrete.