Carbonation Curing Research Articles

Effect of carbonation curing on the characterization and properties of steel slag-based cementitious materials

Steel slag (SS)-based cementitious materials usually exhibit poor bulk stability, poor early activity and low mechanical strength, which greatly limits the consumption of SS in construction materials. Carbonation curing can not only control volume expansion but also improve the mechanical properties and durability of SS-based cementitious materials. First, the physicochemical properties of the SS were summarized. Then, the reaction mechanism of carbonation curing was analyzed. Next, the mineral composition, microstructure, morphology and CO2 uptake of the SS-based materials during carbonation curing were discussed, and the effects of carbonation curing on the mechanical properties, volume stability and durability of the SS-based materials were investigated. Finally, some suggestions for the application of carbonation curing in SS-based materials were given. The development and application of carbonation curing in SS-based materials can achieve the large-scale utilization of SS in cementitious materials and the effective reduction of CO2 emissions.

The formation of CaCO3-based binder by carbonating high-dosage Ca(OH)2 + slag + NaHCO3 (HCHSN) cement paste

Normally, carbonation can cause the decalcification of C-(A)-S-H gel of alkali-activated cement and the degradation of mechanical properties. While, we propose another possibility to form CaCO3-based binder by carbonating the alkali-activated slag cement of high-dosage Ca(OH)2 (30%) + slag (70%) + NaHCO3 (5.11% by weight of Ca(OH)2 and slag) (HCHSN) in this study. The results supported that the compressive strength and volume stability of HCHSN cement paste can be improved by the carbonation curing and the carbonated HCHSN cement paste could reach a maximum compressive strength of 32.4MPa. According to the micro-analysis of XRD, TGA, FTIR, 1H NMR, BSE and SEM, the carbonated HCHSN cement paste was developed into a CaCO3-based binder with a CaCO3 content approaching 60% (based on the mass of the samples heated to 800℃). NaHCO3 played a key role in the formation of the CaCO3-based binder, which not only accelerated the carbonation rate, but also promoted the carbonation of slag. The eco-efficiency assessment showed that compared to the production of 12.5kg CO2 /MPa/t from carbonated ordinary Portland cement, the carbonated HCHSN cement paste only produced 3.5kg CO2 /MPa/t, making it a very green CaCO3-based cementitious materials.

Improving the Performance of Mortar under Carbonization Curing by Adjusting the Composition of Ternary Binders

As the most widely used building material, cement has attracted the attention of scholars because of its large carbon emission. To alleviate the problems of carbon emission and limited resource use caused by cement production, this study focuses on the performance of mortar after carbonization curing by regulating the composition of ternary binders. Testing involved mechanical parameters, carbon shrinkage, water absorption, hydration product, microstructure, adsorption of carbon dioxide, calcium carbonate content, and carbonization degree of mortar, as well as comparisons with the effect of calcium carbide slag and sintered red mud. We carried out several studies which demonstrated that carbonization curing and adjusting the content of calcium carbide slag and sintered red mud were beneficial to improve the mechanical properties, peak load displacement, slope, elastic energy, plastic energy, carbon shrinkage, carbon dioxide adsorption, calcium carbonate content, and carbonization degree of mortar, while the addition of calcium carbide slag and sintered red mud increased the water absorption of mortar, and the greater the dosage, the greater the water absorption. Meanwhile, adding 25%–50% calcium carbide slag and sintered red mud still had negative effects on the mechanical properties of mortar. But carbonation curing and the addition of calcium carbide slag and sintered red mud could promote the hydration reaction and consume calcium hydroxide formed by hydration to form calcium carbonate. When the dosage was 50%, the carbon dioxide adsorption capacity, calcium carbonate content, and carbonization degree of calcium carbide slag mortar were higher than those of sintered red mud mortar, which increased by 29.56%, 102.73%, and 28.84%, respectively. By comparison, calcium carbide slag and sintered red mud still showed superior carbon sequestration capacity, which was higher than fly ash and Bayer red mud. From the experiment, we came to realize that adjusting the composition of cementitious materials could realize the carbon sequestration of cement-based materials and promote the road toward low-carbon sustainable development of cement.

Study on the properties and eco-sustainability of early-age carbonation cured cement paste with recycled concrete slurry waste substitution

The reduced early-age properties of cementitious materials substituted recycled concrete slurry waste (RCSW) hinder its utilisation, which can be further improved via early-age carbonation curing with benefits from sequestering the CO2. This study aims to compressively investigate the effectiveness and environmental impact of early carbonation curing on three replacement ratios and three types of treatments of RCSW including sieving, shearing and ball milling with standard curing. In addition to mechanical properties, hydration properties, microstructure characteristics, and carbon sequestration of the treated-RCSW replaced cement paste after different curing methods were investigated and compared. The results showed that, compared to substitution ratios of 30 % and 45 %, cement paste with a 15 % RCSW substitution ratio exhibited higher strength. Furthermore, compared to standard curing, the carbonation curing method effectively improved the early strength and overall performance of the cement paste, with the early strength under carbonation curing at a 15 % RCSW substitution rate being about 89 % higher than that of standard curing. According to economic and environmental calculations, RCSW substitution could effectively reduce carbon dioxide emissions, and the use of carbonised curing methods enabled the cement paste to effectively absorb carbon dioxide.

Electrical resistivity of cement-based materials through ion conduction mechanisms for enhancing resilient infrastructures

Cement-based materials (CBM) in humid environments, influenced by their inherent defects and the presence of pore solution, exhibit poor electrical insulation performance. Low electrical resistivity of cement-based materials poses a threat to the safety of resilient infrastructures, shortens the lifespan of materials, and increases the costs of maintenance and repair. In this work, we first elucidate two primary mechanisms for enhancing electrical resistivity: (1) inhibition of ion electromigration and (2) disruption of conduction paths. We then systematically summarize and discuss 16 potential methods for improving their electrical resistivity based on these mechanisms. It is indicated that among these 16 methods, early carbonation curing, the addition of high-activity mineral admixtures, and surface hydrophobic modification are particularly effective approaches. The combination of two or more methods can simultaneously exert their functions, thus maximizing the overall effectiveness. Future work is outlined with the aim of meeting the growing demand for cement-based materials with high electrical resistivity in the construction of resilient infrastructures.

Ultrasonic Non-Destructive Testing of Accelerated Carbonation Cured-Eco-Bricks

This study aimed to investigate the behavior of accelerated carbonation-cured laboratory specimens using the ultrasonic non-destructive testing (UNDT) method and compare the results with the destructive testing (DT) method. The materials used in the study included a blend of lime kiln dust and ground granulated blast furnace slag (LKD-GBFS) wastes, natural fine aggregate (sand), and alternative fine aggregates from waste tires. The chemical analysis of the LKD and GBFS samples highlighted them as suitable alternatives to OPC, hence their utilization in the study. A 60:40 (LKD-GBFS) blending ratio and a 1:2 mix design (one part LKD-GBFS blend and two part sand) was considered. The natural fine aggregate was partially replaced with fine waste tire rubber crumbs (TRCs) in stepped increments of 0, 5, and 10% by the volume of the sand. The samples produced were cured using three curing regimens: humid curing (HC), accelerated carbonation curing (ACC) with no water curing (NWC) afterwards, and water curing after carbonation (WC). From the results, an exponential model was developed, which showed a direct correlation between the UNDT and DT results. The developed model is a useful tool that can predict the CS of carbonated samples when cast samples are unavailable. Lastly, a total CO2 uptake of 15,912 g (15.9 kg) was recorded, which underscores ACC as a promising curing technique that can be utilized in the construction industry. This technique will bring about savings in terms of the time required to produce masonry units while promoting a change in the basic assumptions of a safer and cleaner environment.

Developing sustainable steel slag-based aerated concrete: Effects of accelerated carbonation on performance and carbon emissions

This research undertakes an in-depth examination of the properties of carbonated steel-slag aerated concrete (CSSAC), the mineral composition and microstructure were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), life cycle assessment (LCA) also employed for evaluating its environmental impacts. Results revealed that a strength of 6.6 MPa and a dry density of 958 kg/m3 for CSSAC was achieved through carbonation curing, utilizing a 30 vol% CO2 concentration at ambient pressure for a duration of 24 h. Nonetheless, elements such as high water-solid ratio, cement content, and foaming agent content were found to negatively affect the strength development. Furthermore, the overuse of lime as a cement substitute formed a dense pore structure on the surface layer, consequently lowering CO2 sequestration efficiency. It was found that compressive strength was enhanced and water absorption was reduced by 66 % with calcium stearate, through effective pore structure optimization. Significantly, the carbon footprint of CSSAC stood at a minimal 0.0673 kg∙CO2∙eq/kg, achieving a substantial 73.36 % reduction when compared with its original carbon footprint. This adoption of carbonation curing effectively mitigated the carbon footprint of the product, offering actionable insights for the manufacturing of zero-carbon and even negative-carbon building materials.

Accelerated carbonation curing of biochar-cement mortar: Effects of biochar pyrolysis temperatures on carbon sequestration, mechanical properties and microstructure

The integration of biochar with accelerated carbonation curing (ACC) has the potential to reduce the carbon footprint of cementitious materials. However, the effects of biochar pyrolysis temperatures on the performance of accelerated carbonation-cured cementitious materials remain unclear. In this study, corn straw was used as the raw material to prepare biochar at 300℃, 500°C, and 700°C for incorporation into cement mortar. The effects of biochar pyrolysis temperatures on carbon sequestration, mechanical properties and microstructure of cement mortar were investigated at 3 days and 28 days of ACC. The results showed that incorporating the biochar at 500℃ into cement mortar exhibited the highest carbon sequestration with up to 31.6 % increase compared to 300℃ and 700℃. The porosity of biochar dominated the inward CO2 transport rather than the chemisorption effect of oxygen-containing functional groups under ACC. The biochar at 500℃ showed the most improvement in compressive strength. The biochar at 700℃ enhanced the early-stage compressive strength due to its significant hydrophobicity at high dosages (7 % by mass), while excessive amounts adversely affected the overall compressive strength. The incorporation of biochar effectively reduced the porosity of cement matrix and narrowed the differences in carbonation degree among layers, with the biochar at 500 °C showing the best results due to its larger specific surface area and pore volume. This study provides insights to further advance the efficient application of biochar in low-carbon building materials.

Effects of Curing Regimes on Calcium Oxide-Belite-Calcium Sulfoaluminate-Based Aerated Concrete.

This study delves into the effects of carbonation curing and autoclave-carbonation curing on the properties of calcium oxide-belite-calcium sulfoaluminate (CBSAC) cementitious material aerated concrete. The objective is to produce aerated concrete that adheres to the strength index in the Chinese standard GB/T 11968 while simultaneously mitigating CO2 emissions from cement factories. Results show that the compressive strength of CBSAC aerated concrete with different curing regimes (autoclave curing, carbonation curing, and autoclave-carbonation curing) can reach 4.3, 0.8, and 4.1 MPa, respectively. In autoclave-carbonation curing, delaying CO2 injection allows for better CO2 diffusion and reaction within the pores, increases the carbonation degree from 19.1% to 55.1%, and the bulk density from 603.7 kg/m3 to 640.2 kg/m3. Additionally, microstructural analysis reveals that delaying the injection of CO2 minimally disrupts internal hydrothermal synthesis, along with the formation of calcium carbonate clusters and needle-like silica gels, leading to a higher pore wall density. The industrial implementation of autoclavecarbonation curing results in CBSAC aerated concrete with a CO2 sequestration capacity ranging from 40 to 60 kg/m3 and a compressive strength spanning from 3.6 to 4.2 MPa. This innovative approach effectively mitigates the carbon emission pressures faced by CBSAC manufacturers.

Accelerated carbonation of alkali-activated vibro-compacted pervious concrete paving blocks

This study explores the use of an accelerated carbonation curing method to enhance the performance of non-structural precast alkali-activated fly ash pervious concrete paving blocks. Using a predefined production process, pervious paving blocks measuring 200 mm × 100 mm × 60 mm were manufactured and subjected to a 3-stage curing process. The blocks were produced with a dry consistence to allow for vibrocompaction, closely mirroring the manufacturing techniques used in the precast industry and enabling immediate demoulding. Initially, all blocks underwent thermal curing at 70 °C for 24 hours, followed by storage in a climatic chamber (20 ± 3 °C, 65 ± 10 % relative humidity) for 7–14 days. Finally, they were exposed to a carbonation chamber with 5 % CO2 at 23 ± 2 °C, and 60 ± 10 % RH for up to 7 days. Blocks cured without carbonation served as control specimens. All blocks were tested following the European standard EN 1338, which governs the conformity of conventional concrete pavement blocks. Additional properties such as water permeability and water stability were also assessed. The results demonstrated that the accelerated carbonation curing significantly improved the performance of the blocks. Increases of 30 % and 60 % in compressive and splitting tensile strengths, respectively, were reported for the 7-day CO2-cured blocks when compared to their control counterparts. The 7-day carbon-cured blocks showed significantly improved abrasion resistance, with mass loss due to abrasion decreasing from 8.2 % to 5.6 % with 7 days of CO2 exposure. Additionally, microstructural enhancements were observed for the carbonated specimens, positively impacting their overall performance and making them compliant with the standard for practical paving block applications. However, further research is recommended to explore automation in the production process to ensure consistent results and facilitate future standardisation and certification of these blocks.

Research progress on the application of low-reactivity minerals in carbonation-cured cement-based materials

Cement is essential for the construction industry, but its production process generates a large amount of CO2, adversely affecting the environment. To address the issue above, carbonation curing serving as one of the efficient carbon reduction approaches is widely adopted benefiting from its advantages of rapidly realizing carbon sequestration and enhancing the performance of cementitious materials. Numerous studies have indicated that the addition of low-reactivity minerals such as limestone, quartz, sandstone, and glass powder accelerates the carbonation reaction of cement composites. However, there is a lack of reviews on the application of low-activity minerals in carbonation-cured cementitious materials. Therefore, this paper presents a comprehensive review regarding the research progress on the application of low-reactivity minerals in carbonation-cured cement-based materials for the first time. This review first introduces the effect of low-activity minerals on the performance of carbonation-cured cement composites. Subsequently, the related mechanism is analyzed. Finally, the future research directions and challenges in this field are emphasized. This work provides insights and references for the application of low-reactivity minerals in carbonation-cured cement-based materials, thus contributing to carbon emission reduction in the cement industry.

MgO activated calcined marine clay and its carbonation

Marine clay, a common waste product abundantly available in coastal regions, can serve as an alternative silica source after activation due to its pozzolanic reactivity. In this study, a binder comprising reactive MgO cement and thermally activated marine clay (AMC) was developed. It was found that the developed MgO-AMC binder with a mass ratio of MgO to AMC of 0.4 to 0.6 achieved a 28-day compressive strength of 20.4 MPa under ambient curing. Through accelerated carbonation curing, the highest 28-day compressive strength increased by 45%, and the highest carbon sequestration ratio reached 11.8%. The phase evolution and microstructural development of hydrated/carbonated binder were comprehensively investigated by TG-IR, XRD, NMR, and SEM-EDS. In addition, thermodynamic modelling was performed to further understand the phase assemblage of the hydrated binder, and indicated that M-A-S-H phase was thermodynamically more stable in the developed binder.

Production of low-carbon cement composites using red sandstone: CO2 storage and performance analysis

Carbonation curing is currently one of the most effective methods for reducing carbon and absorbing carbon dioxide in cement-based materials. This study evaluated the macroscopic, microscopic, and thermal properties of red sandstone and limestone with different dosages under different curing methods. The results show that the carbonation rate is higher when 20 % red sandstone is added, and the carbon fixation amount is the highest. The inclusion of red sandstone provides more nucleation sites for the formation of carbonation product silica gel. At 600°C, the strength reduction of the carbonation samples is lower than that of the sealed samples, and the carbonation products are more resistant to high temperatures. Furthermore, the relationship between the microscopic, macroscopic, and thermal properties of red sandstone and limestone under different curing methods is explored. This study provides a new approach to the utilization of red sandstone resources.

Enhancing cement-based materials hydration and carbonation efficiency with pre-carbonated lime mud

Lime mud (LM) is a highly alkaline solid waste generated during the papermaking process, and its direct application in cement-based materials can result in insufficient material properties. Pre-carbonation can reduce the alkalinity of LM and improve its ability as a supplementary cementitious material. This study explored the potential of pre-carbonated lime mud (CLM) to partially replace Portland cement under normal and carbonation curing. It was found that CLM absorbed some CO2 and reduced a small amount of alkalinity after pre-carbonation treatment. Under normal curing conditions, LM can promote the hydration reaction at an early age but inhibit subsequent cement hydration due to its alkalinity. In contrast, CLM significantly alleviated the negative impacts of directly incorporating LM into Portland cement. Under carbonation curing conditions, a significant improvement in the compressive strength of cement-based materials containing LM and CLM was observed. The alkaline properties and nucleation effects of CLM and LM enhanced CO2 sequestration efficiency. Especially after 14 days of carbonation curing, the sample with CLM exhibited higher CO2 uptake and better mechanical properties than the sample with LM. This study provides a new solution to improve the resource utilization of LM and mitigates the negative impacts of LM on cement-based materials.

Investigating key factors for superior CRMC-based mortars cured under CO2 pressurized environment

An exploratory programme was undertaken to individually test the influence of reactive magnesia to waste-based material (biomass fly ash) ratio, water to solids in binder ratio, static compaction pressure, accelerated carbonation curing period, and curing temperature, on the compressive strength results of Carbonated Reactive Magnesia Cement (CRMC)-based mortars. Subsequently, the observed optimal conditions of each parameter were combined to assess their influence when applied together. A total of twenty-four mixture labels were designed, with specimens moulded under static compaction pressure and subjected to a pressurized accelerated carbonation curing under controlled conditions. The devised mortars were evaluated through compressive strength tests, and the microstructure was carried out through TG-DTG, ATR-FTIR, XRD, SEM-EDX, and MIP analyses. The results demonstrated that none of the tested influencing factors can be exclusively considered as the sole determinant for the compressive strength outcomes. Thus, this study highlights the importance of thoroughly considering any modifications in both mixture design and accelerated carbonation curing conditions to achieve the optimal properties of CRMC-based mortars. Additionally, the devised CRMC-based mortars exhibited favourable binding properties with biomass fly ashes, allowing for its secondary use and contributing to waste circularity by avoiding landfill disposal, supporting the development of the waste circularity and CO2 sequestration through mineralization in carbonated materials.

Mechanical, freeze-thaw resistance and heavy metals leaching properties of alkali-activated recycled concrete powder solidified sludge

Solidified sludge was an efficient method to consume the large amount of sludge, which can be used as the subgrade filler in road engineering. However, the traditional solidified materials, such as cement and lime, consumed a large amount of natural resources and increased carbon emissions. This study used the alkali-activated recycled concrete powder (ARCP) to solidify sludge, which could be used as a potential subgrade stabilization filler. The optimal factors of ARCP were firstly determined by orthogonal test according to the compressive strength. Then the influences of different ARCP dosage, sludge moisture content and curing method on the mechanical properties, freeze-thaw resistance and heavy metals immobilization of the ARCP solidified sludge (ARCPS) were investigated. At last, microstructures of ARCPS were analyzed by SEM, XRD and TG-DTG tests. The experimental results demonstrated that the optimal mixture for ARCP: the silicate modulus of 1, liquid-solid ratio of 0.48 and calcium hydroxide content of 3 %. The solidified process by ARCP improved the mechanical properties and freeze-thaw resistance of ARCPS greatly. The 7 d unconfined compressive strength of ARCPS could reach 1305–2033 kPa when the sludge moisture content was 15 %, which meet the requirement of 500 kPa from the Chinese standard. The frost heaving rates of ARCPS were between non-frost heaving and mild frost heaving. The sludge moisture content was the most important factor affecting the freeze-thaw resistance of ARCPS. The properties of ARCPS were further improved after carbonation curing. The leaching mass concentration of heavy metals decreased significantly after the solidification of sludge. After 5 freeze-thaw cycles, the heavy metal leaching concentration increased but was still met the requirement of standards. SEM results showed that the surface of carbonated ARCPS was covered by dense scale-like carbonation products, which further enhanced the strength and freeze-thaw resistance of ARCPS. The results can be used to guide the application of sludge and ARCP in construction.

Understanding mechanism on carbonation curing for Portland cement through phase profiling via QXRD analysis and thermodynamic modeling

The mechanism of early age accelerated carbonation cured ordinary Portland cement mixtures is evaluated using experimental and thermodynamic modeling. This study considered three early precuring conditions, two carbonation curing periods, four CO2 concentrations, and a 0.5 w/c ratio. The investigation was conducted using phase profiling of mixtures based on QXRD results and developed a thermodynamic model that simulated the experimental conditions. The mechanical characteristics of carbonation-cured mortar specimens, including compressive strength, elastic modulus, shrinkage, and mass change, were evaluated. The results revealed that short precuring durations hindered carbonation, resulting in lower CO2 uptake, strength, elastic modulus and higher shrinkage. Increasing the precuring period from six-hours to one or three days resulted significant amount of CaCO3 precipitation on the surface of the specimen and appropriate mechanical properties. One day precuring followed by one day carbonation with a 10 % CO2 exposure resulted in a higher calcite precipitation on the surface with less depth of penetration. It was found that a balance between drying-induced degradation and microstructure densification due to calcite precipitation is crucial. An appropriate precuring duration, for each binder type and mix proportion, should be applied to achieve desired properties and CO2 uptake in carbonation-cured cementitious materials.

Carbonation curing of cement-based materials by using potassium glycine solution: Uniformly CO2 sequestration and secondary strengthening

In this research, an internal carbonation curing method was proposed to achieve inside-outside synergistic carbon capture and performance improvement of cement-based materials. Potassium glycine (KG) solution with various concentrations was used as the CO2 carrier. The results indicate that the addition of CO2-rich KG solution increases 7-d and 28-d compressive strength by 29.8% and 16.2%, as well as achieving an overall CO2 uptake of 4∼11% in cement paste. However, at higher KG concentrations, the rapidly generated amorphous calcium carbonate covers the surface of cement particles, which shortens the setting time and inhibits early-age hydration. The presence of carbamate in CO2-rich KG solution improves the stability of metastable CaCO3 polymorphs and prolongs the period of dissolution-recrystallization. Calcite generated by the slowed recrystallization within 14 days having a filling and binding ability in the cement matrix, significantly reducing porosity and providing a secondary strengthening effect.

Fast-Hardening Production of High-Strength BOFS Aggregates by High-Temperature Carbonation Curing

Fast-Hardening Production of High-Strength BOFS Aggregates by High-Temperature Carbonation Curing

Effects of wet carbonation with ethanol solution on the mechanical, durability properties, and microstructure of recycled concrete aggregates and derived block products

The carbonation treatment of recycled concrete aggregates (RCA) can significantly enhance their properties and reusability. To improve carbonation efficiency, a wet cyclic carbonation method using ethanol solution was proposed to treat RCA and a wet carbon curing method was applied to its product, recycled blocks (RB). The results showed that wet carbonation with 30 % ethanol solution for 10 min significantly reduced RCA’s water absorption and crushing index and increased its apparent density. This is attributed to ethanol’s high carbon-solubilizing properties, which allow the RCA to generate more calcium carbonate precipitates to fill the voids and optimize the pore structure. When the concentration of ethanol solution was increased above 50 %, the improvement was inefficient and limited. In addition, the second cycle of wet carbonation can further improve the properties of RCA. Optimally processed RCA was used to make recycled masonry blocks. The 10 min wet carbonation curing proved beneficial to the mechanical properties of RB and also improved its resistance to shrinkage and salt freeze-thaw. This rapid method enhances RCA construction materials' performance and durability, improving industrial use in sustainable construction materials.