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Early age carbonation curing of slag-cement concrete was investigated to assess the feasibility of binding C[O.sub.2] in slag-cement building products while improving their short-term and long-term performances. Four binder types were compared: an ordinary portland cement; an 85/15 slag cement: a 75/25 slag blend; and a 50/50 slag blend. A 2-h carbonation-curing treatment allowed concretes to bind 8-10% C[O.sub.2] by mass of binder and attain as much as 82% of the 24-h hydration strength. The subsequent strength development of carbonated concrete was slower in the first 24 h possibly due to the carbonate buildup, but it was comparable to the conventionally hydrated concrete after 28 days. The carbonated concrete was shown to have a fracture toughness comparable to that of the hydrated concrete. The freeze/thaw durability of the concrete in deicing salt solution was vastly improved by the carbonation treatment. The pH of the carbonated concrete was reduced but was still above the threshold level required for the passivation of iron. The use of slag in carbonation curing is beneficial to strength gain, shrinkage reduction, and deicing salt resistance. DOI: 10.1061/(ASCE)MT.1943-5533.0000018 CE Database subject headings: Cement; Concrete; Mechanical properties; Durability; Carbon dioxide; Carbonation. Author keywords: Carbonation curing; Slag cement; Concrete; Mechanical properties; Durability; Carbon dioxide binding.

The possibility of using a carbonated ladle slag as a fine aggregate in concrete was investigated. The slag was treated with carbon dioxide to reduce the free lime content while binding gaseous C[O.sub.2] into solid carbonates. The treatment took place with either a high concentration of C[O.sub.2] at 500 kPa for 2 h or with a low concentration of C[O.sub.2] at atmospheric pressure for 56 days. It was found that C[O.sub.2] uptake by the slag particles between 300 and 600 [micro]m and by the slag particles smaller than 75 [micro]m were about 4.2 and 15.6% of their mass, respectively. The extractable CaO contents were estimated by titration and were found to be significantly reduced by carbonation treatment. The carbonated ladle slag was used as a fine aggregate in zero-slump press-formed compact mortar samples and compared to similar samples containing a control river sand. The 28-day strengths of the mortars made with the carbonated slag sand were comparable to the strengths of the normal river sand mortars. The use of carbonated ladle slag as a fine aggregate in concrete is shown to be a novel way of sequestering C[O.sub.2] in a beneficial manner. DOI: 10.1061/(ASCE)0899-1561(2009)21:11(657) CE Database subject headings: Carbonation: Aggregates: Concrete; Slag.

The carbonation behavior of six cementitious materials was examined (CSA Type 10 cement, CSA Type 30 cement, fly ash, ground granulated blast furnace (GGBF) slag, electric arc furnace (EAF) slag, and hydrated lime) for applicability to C[O.sub.2] sequestration applications. No-slump press-formed compacts and loose powders were subjected to 100% C[O.sub.2] at a constant pressure of 5 bar for 2 h. The C[O.sub.2] contents of the as-received and the carbonated materials were measured. It was found that the cements, fly ash, and electric arc furnace slag could each show C[O.sub.2] uptake on the order of 12%, while the lime achieved nearly 40%. The blast furnace slag managed 7% uptake. The carbon uptakes achieved were significantly lower than the theoretical maximum as determined by chemistry. The 2 h carbonation produced high early age strength in cements and hydrated lime, which can be used as structural materials. The strength gain in fly ash, EAF slag, and GGBF slag was nevertheless not sufficient. X-ray diffiaction analysis determined that the primary carbonation product formed was calcite, while [C.sub.3]S, [C.sub.2]S, and Ca[(OH).sub.2] were the phases consumed. Scanning electron microscopy observations considered the morphology of the carbonation products and the degree of reaction in terms of microstructure characteristics. CE Database subject headings: Calcium carbonate: Carbon dioxide: Carbonation: Portland cement; Slag; Fly ash: Lime.

Early age carbonation curing of slag-cement concrete was investigated to assess the feasibility of binding CO2 in slag-cement building products while improving their short-term and long-term performances. Four binder types were compared: an ordinary portland cement; an 85/15 slag cement; a 75/25 slag blend; and a 50/50 slag blend. A 2-h carbonation-curing treatment allowed concretes to bind 8–10% CO2 by mass of binder and attain as much as 82% of the 24-h hydration strength. The subsequent strength development of carbonated concrete was slower in the first 24 h possibly due to the carbonate buildup, but it was comparable to the conventionally hydrated concrete after 28 days. The carbonated concrete was shown to have a fracture toughness comparable to that of the hydrated concrete. The freeze/thaw durability of the concrete in deicing salt solution was vastly improved by the carbonation treatment. The pH of the carbonated concrete was reduced but was still above the threshold level required for the passivation of iron. The use of slag in carbonation curing is beneficial to strength gain, shrinkage reduction, and deicing salt resistance. [ABSTRACT FROM AUTHOR]