• Journal of the Korea Institute of Building Construction
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• v.6 no.4 s.22
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• pp.61-68
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• 2006

Recently, there have been many studies about recycling cementitious powder from concrete waste(hereinafter referred to as waste powder), generated after recycle aggregate production. Previous studies showed that when the heating process of waste powder at $700^{\circ}C,\;Ca(OH)_2$ in paste is dehydrated making possible the restoration of hydraulic properties. Recycled cement with hydraulic properties restored is thought to be re-hydrated through the mechanism of hydration, which is almost similar in Portland cement. This clearly suggests that the hydrate of recycled cement is alkali in type. Like in general concrete, if recycled cement is used as a structural material, resistance performance against carbonation or neutralization by $CaCO_3$ in air probably would be most influential to the life of steel-reinforced concrete structure. Thus the purpose of this study is to make an experimental review on chemical properties of recycled cement, manufactured with concrete waste as base material, and investigate the durability of concrete using recycled cement through evaluating the cement's performance of resistance to carbonation in accordance with its accelerating age. Based on its results, further, the study seeks to provide basic information about ways of utilizing recycled cement.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.324-331
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• 2023

In this study, the hydration and carbonation properties of circulating fluidized bed boiler (CFBC) ash with different free-CaO contents were investigated. In addition, the possibility of utilizing CFBC ash with a high free-CaO content as a cementitious material was investigated by carbonation curing as a pretreatment. The CFBC ash with high free-CaO content exhibited rapid setting behavior and low early compressive strength when mixed with cement. For CFBC ash with high free-CaO content, carbon dioxide capture increased with the duration of carbonization curing. In addition, the free-CaO value decreased together, indicating that the free-CaO reacted with carbon dioxide. When the CFBC ash with high free-CaO content was pretreated by carbonation, no fresh set appeared, and the initial compressive strength was improved. From the results of this study, it is confirmed that CFBC ash with high free-CaO content has a high potential to be utilized as a cementitious material through proper carbonation curing.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.257-262
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• 2015

Recently the world wide efforts reduce occurrence of $CO_2$; global warming main reason. The aim of this study is to improve recycling rate of the fly ash (FA) and fused waste slag (FWS) from the power plant and to carbonate under supercritical condition ($40^{\circ}C$, $80kgf/cm^2$ pressure, 60 min) for $CO_2$ fixation. Specimens of mortar with various mixing ratios of FA, FWS (from 100:0 to 20:80 in 5 steps of 20 % reduction each time), distilled water and 3 M NaOH alkali activators were prepared. As a result, the proportion of weight change ratio increases with CaO content, to 12 % after carbonation under the supercritical condition. There is difference of compressive strength between the carbonated and the alkali activator mortar specimens. The stabilization of $CO_2$ fixation through carbonation which could confirm the applicability of the eco-friendly materials without loss of compressive strength.

• Journal of the Korean Ceramic Society
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• v.41 no.12 s.271
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• pp.889-892
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• 2004

Acicular type aragonite precipitated calcium carbonate was synthesized by carbonation reaction of $Ca(OH)_2$ slurry and $CO_2$ gas. As increasing the initial concentration of $Mg^{2+}$ ion, calcite crystal phase substantially decreased while that of aragonite crystal phase increased. According to XRD and EDS analysis, it was found that the addition of $MgCl_2$ induced the $Mg^{2+}$ ion to substitute in $Ca^{2+}$ ion site of calcite lattice then the unstabled calcite structure be resolved, consequently the growth of calcite structure is interrupted while the growth of aragonite structure is expedited.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.226-233
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• 2023

In this study, two phases were conducted to investigate the direct injection of gaseous CO₂ into cement mortar. The aim was to advance carbon capture, utilization, and storage (CCUS) technology by harnessing industrial waste CO₂ from the domestic ready-mixed concrete industry. In the first phase, the factors influencing the physical properties of cement mortar when using gaseous CO₂ were identified. This included a review of materials to achieve physical properties comparable to a reference formulation. As a result of this phase, it was confirmed that traditional approaches, such as adjusting the water-to-cement ratio, had limitations in achieving the desired physical properties. Consequently, the second phase focused on the optimization of CO₂-injected mortar. This involved studying the CO₂ application and mixing method for cement mortar. Changes in properties were observed when gaseous CO₂ was injected into the mortar. The optimal injection quantity and time to enhance the compressive strength of mortar were determinded. As a result, this study indicated that an extra mixing time exceeding 120 seconds was necessary, compared to conventional mortar. The optimal CO₂ injection rate was identified as 0.1 to 0.2 % by weight of cement, taking both flowability and compressive strength performance into account. Increasing the CO₂ injection time did not further enhance strength. For this approach to be employed as a CCUS technology, additional studies are required, including a microstructural analysis evaluating the amount of immobilized CO₂.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.201-210
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• 2014

The present study proposes a phased model to assess the lifecycle $CO_2$ amount of concrete structures. The considered system boundary is from cradle to recycling, which includes constituent material, transportation, batching and mixing in ready-mixed concrete plant, use and demolition of structure, and crushing and recycling of demolished concrete. The $CO_2$ uptake of concrete by carbonation during lifetime (40 years) of a structure and the recycling life (20 years) after demolition is estimated using a simple approach generalized to predict the carbonation depth from the surfaces of concrete element and recycled aggregates. Based on the proposed phased model, a performance evaluation table is realized to straightforwardly examine the lifecycle $CO_2$ amount of concrete structures. The proposed model demonstrates that the contribution of ordinary portland cement (OPC) to lifecycle $CO_2$ emission of the concrete structure occupies approximately 85%. Furthermore, the $CO_2$ uptake is estimated to be approximately 15~18% of the lifecycle $CO_2$ emissions of concrete structures, which corresponds to be 19~22% of the emissions from OPC production. Overall, the proposed $CO_2$ performance table is expected to be practically useful as a guideline to determine the $CO_2$ emission or uptake at each phase of concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.737-740
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• 2006

A cement which is used in construction and a concrete which is a hydration product of cement is considered anti-environmental materials because of lots of $CO_2$ emission in progress of producing and making them. But a concrete absorbs the $CO_2$ gas in atmosphere after hydration and in its lifetime. Based on Papadakis' theses, this research is carried on calculation of the $CO_2$ absorption quantity in concrete. Also, the emission of $CO_2$ was calculated by cement manufacture. As a result, It is said that the $CO_2$ which was emitted during cement manufacturing, was absorbed the 53% of emission quantity by the carbonation of concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.166-167
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• 2022

The International Energy Agency(IEA) recommends that intergovernmental agreements reduce CO2 emissions by 2050 to about 50% in 2005 in its report. To realize these demands, it is suggested to actively utilize energy efficiency improvement technology, renewable energy, nuclear power, carbon dioxide capture & storage technology (CCS). In the field of building materials and cement, mineral carbonization technology is widely used. Inorganic by-products applicable to greenhouse gas storage include waste concrete, slag, coal ash, and gypsum. If the Mineral Carbonation Act is used, it is expected that about 12 million tons of greenhouse gases can be immobilized every year. Greenhouse gas immobilization using cement hydrate can be immobilized by injecting carbon dioxide into the hydrated products C-S-H, and Ca(OH)2. In the case of immobilization through concrete carbonization, a carbon dioxide promotion test is used, which is often different from the actual carbon dioxide carbonization reaction. If the external carbon dioxide concentration is abnormally higher than the reality, it is thought that it will be different from the actual reaction. In this study, the carbonation phenomenon according to the concentration and identification of the carbon dioxide reaction mechanism of cement hydrate was to be considered.

• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.279-286
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• 2017

This review paper evaluates different kinds of synthesis methods for calcite precipitated calcium carbonates by using different materials. The various processing routes of calcite with different compositions are reported and the possible optimum conditions required to synthesize a desired particle sizes of calcite are predicted. This paper mainly focuses on that the calcite morphology and size of the particles by carbonation process using loop reactors. In this regard, we have investigated various parameters such as $CO_2$ flow rate, Ca $(OH)_2$ concentration, temperature, pH effect, reaction time and loop reactor mechanism with orifice diameter. The research results illustrate the formation of well-defined and pure calcite crystals with controlled crystal growth and particle size, without additives or organic solvents. The crystal growth and particle size can be controlled, and smaller sizes are obtained by decreasing the Ca $(OH)_2$ concentration and increasing the $CO_2$ flow rate at lower temperatures with suitable pH. The crystal structure of obtained calcite was characterized by using X-ray diffraction method and the morphology by scanning electron microscope (SEM). The result of x-ray diffraction recognized that the calcite phase of calcium carbonate was the dominating crystalline structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.18-25
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• 2020

The purpose of this study is to investigate the mechanical and carbon-capture properties of foam concrete containing stainless steel argon oxygen decarbonization(AOD) slag. AOD slag was used as a binder, and foam concrete having a foaming ratio of 69 ± 0.5 % and a slurry density of 573.2 to 578.6 kg / ㎥ was produced. In order to examine the effect of carbonation, blended specimen was cured by two types : normal curing and CO₂ curing. As a result of the experiment, the specimens incorporating AOD slag showed higher compressive strength than Plain after CO₂ curing. According to the analysis of the image of foam concrete, it was confirmed that the ST30 has a lower total pore volume and average pore size than plain, resulting in high compressive strength. The SEM analysis confirmed the formation of calcite by carbonation of AOD slag. Through the thermogravimetric analysis, the increase of CO₂ uptake was confirmed by the incorporation of AOD slag. Foam concrete has a higher porosity than normal concrete, so it is expected that carbon-capture performance can be improved by using a AOD slag.