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An important part of improving the embodied carbon of the built environment is reducing carbon emissions associated with concrete. The long-term limitations around the availability of supplementary cementitious materials (SCMs) to replace portland cement have driven the search for additional innovative approaches. The beneficial use of carbon dioxide (CO2) in ready mixed concrete production has been developed and installed as retrofit technology with industrial users. An optimum dose of CO2 added to concrete as an admixture leads to the in-place formation of mineralized calcium carbonate (CaCO3) and can increase the concrete compressive strength. The improved performance can be leveraged to design concrete mixture proportions for a more efficient use of portland cement, along with the use of CO2 to reduce the carbon footprint of concrete. One producer has used the technology, starting in 2016, at over 50 plants. More than 3 million m3 of concrete have been shipped with an estimated net savings of 35,000 tonnes of CO2. The concrete produced with carbon dioxide is discussed in terms of the fresh and hardened performance, durability performance, and life cycle impacts. [ABSTRACT FROM AUTHOR]

Wash water is generated as a by-product of ready mixed concrete production. The water can be reclaimed to be used as mix water in new concrete. The properties, durability and sustainability of concrete produced using high solids reclaimed water, subjected to a novel CO2 (carbon dioxide) treatment, as mix water was examined. A simulated reclaimed water with a specific gravity of 1.10 was used as a partial (44%) replacement for mix water in concrete production. A comparison was made between reference concrete, batches made with untreated reclaimed water, and reclaimed water treated with CO2 to either a low or high CO2 uptake. The treatment mineralized CO2 at 5 and 20% by weight of the cement in the reclaimed water solids. The mix designs either included the reclaimed water slurry as a replacement for the mix water or further incorporated a reduction to the virgin binder in proportion to the added reclaimed water solids. The compressive strength was improved with the use of both untreated and treated wash water; it is suggested that the improvements are attributable to cementitious properties of the solids, improved particle packing in the binder phase and an effective reduction of the water to binder ratio. A suite of testing (including RCPT, bulk resistivity, bulk diffusion, abrasion, freeze/thaw, salt scaling, drying shrinkage, carbonation, and corrosion) demonstrated that the durability was not affected by the incorporation of the treated reclaimed water. The treated slurry batches had a 10–11% improvement in the carbon index (kg CO2 embodied/MPa of strength) for the low treatment and 13–14% for the high treatment. [ABSTRACT FROM AUTHOR]

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 feasibility of integrating carbon sequestration into the curing of precast concrete products was investigated. Research assessed the C[O.sub.2] uptake capacities of carbonation-cured concrete masonry units (CMU), concrete pavers, fibreglass-mesh reinforced cement board, cellulose-fibre board, and ladle slag fines. Three curing systems were used: (i)an open-inlet system using pressurized recovered C[O.sub.2];(ii) a closed system using pressurized flue gas with 14% C[O.sub.2]; and (iii) a closed system using dilute C[O.sub.2] under atmospheric pressure. The amount of carbon dioxide that could be sequestered in the annual North American output of the various precast concrete products was estimated. The net efficiency was calculated accounting for C[O.sub.2] emissions penalty resulting from the capture, compression, and potential transport of the curing gases. Carbonation curing of the considered products could result in a net annual C[O.sub.2] sequestration in US and Canada of approximately 1.8 million tonnes if recovered C[O.sub.2] is used and one million tonnes if flue gas is used. Key words: carbon dioxide, carbonation, carbon sequestration, precast concrete, curing. La faisabilite d'inteegrer la sequestration du carbone lors de la cure de produits de beton prefabrique aeete examinee. Cette recherche a evaluee les capacites d'absorption du C[O.sub.2] d'elements de maconnerie en beton muri par carbonatation, de paveesen beton, de panneaux de ciment renforces d'un grillage en fibre de verre, de panneaux en fibres de cellulose et de fines particules de scories de poches de coulee. Trois etuves a durcir ont ete utiliseees : (i) une avec entree libre utilisant du C[O.sub.2] recupere; mis sous pression, (ii) une fermeee utilisant des gaz de chemineie sous pression contenant 14 %deC[O.sub.2],et (iii) une fermeee utilisant du C[O.sub.2] diluee introduit a pression atmospherique. La quantite de gaz carbonique qui pourrait etre sequestree dans la production annuelle nord-ameericaine de beton prefabrique aete estimeie. L'efficacite nette aete calculee en tenant compte de la penalite d'emissions de gaz carbonique decoulant de la capture, de la compression et du transport potentiel des gaz de cure du beton. La cure par carbonatation dans les produits consideres pourrait engendrer une sequestration nette annuelle de gaz carbonique, aux Etats-Unis et au Canada, d'environ 1,8 million de tonnes si le gaz carbonique recupere: est utilise et qu'un million de tonnes de gaz de chemineee est utilise;. Mots-cles: gaz carbonique, carbonatation, sequestration du carbone, beeton prefabrique, cure. [Traduit par la Redaction], Introduction Carbon sequestration has been identified as an important greenhouse gas mitigation strategy for addressing anthropogenic carbon dioxide emissions. Current approaches focus upon carbon capture and storage (CCS) in oceans, [...]

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.

A significant amount of wastewater is generated through the cleaning of equipment utilized within the ready mixed concrete production cycle. The reuse of concrete wash water as mix water is limited by the negative material performance impacts associated with the suspended solids; the effects are exacerbated with increasing solids contents and water aging. A novel carbon dioxide treatment to allow the use of high solids wash water (specific gravity 1.10) as mix water was examined. Seven batches of concrete were produced and compared: a reference mix, two batches with untreated wash water and four batches with CO2 treated wash water. The carbon dioxide treatment mineralized CO2 at 28% by mass of the treated solids. Acceptable concrete was produced through adjusting admixtures for workability. The compressive strength at 1, 7, 28 and 56 days was improved relative to both the reference and the concrete produced with untreated wash water. The suspended solids containing mineralized CO2 served as a viable cement replacement. The avoided cement and bound carbon dioxide served to lower the carbon impact of the concrete by about 14%. The approach allows three waste streams (CO2, wash water and wash water solids) to be reused to produce more sustainable concrete. [ABSTRACT FROM AUTHOR]

A significant amount of wastewater is generated through the cleaning of equipment utilized within the ready mixed concrete production cycle. The reuse of concrete wash water as mix water is limited by the negative material performance impacts associated with the suspended solids; the effects are exacerbated with increasing solids contents and water aging. A novel carbon dioxide treatment to allow the use of high solids wash water (specific gravity 1.10) as mix water was examined. Seven batches of concrete were produced and compared: a reference mix, two batches with untreated wash water and four batches with CO2 treated wash water. The carbon dioxide treatment mineralized CO2 at 28% by mass of the treated solids. Acceptable concrete was produced through adjusting admixtures for workability. The compressive strength at 1, 7, 28 and 56 days was improved relative to both the reference and the concrete produced with untreated wash water. The suspended solids containing mineralized CO2 served as a viable cement replacement. The avoided cement and bound carbon dioxide served to lower the carbon impact of the concrete by about 14%. The approach allows three waste streams (CO2, wash water and wash water solids) to be reused to produce more sustainable concrete. [ABSTRACT FROM AUTHOR]

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]

A correction is presented to the article "NRG COSIA Carbon XPRIZE: carbon-dioxide mineralization in recycled concrete wash water" which appeared in the 20 October 2021 issue.