• Computers and Concrete
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• v.20 no.1
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• pp.99-110
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• 2017

Service life assessments which do not include the synergy between mechanical and environmental loading are neglecting a factor that can have a significant impact on structural safety and durability assessment. The degradation of concrete structure is a result of the combined effect of environmental and mechanical factors. In order to make service life design realistic it is necessary to consider both of these factors acting simultaneously. This paper deals with the advanced modelling of concrete carbonation and chloride ingress into concrete using stochastic 1D and 2D models. Widely accepted models incorporated into the new fib Model Code 2010 are extended to include factors that reflect the coupled effects of mechanical and environmental loads on the durability and reliability of reinforced concrete structures. An example of cooling tower degradation by carbonation and an example of a bended reinforced concrete beam kept for several years in salt fog are numerically studied to show the capability of the stochastic approach. The modelled degradation measures are compared with experimental results, leading to good agreement.

• International Journal of Concrete Structures and Materials
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• v.9 no.3
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• pp.283-294
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• 2015

In the present study, a porous concrete with alkali activated slag (AAS) and coal bottom ash was developed and the effect of carbonation on the physical property, microstructural characteristic, and heavy metal leaching behavior of the porous concrete were investigated. Independent variables, such as the type of the alkali activator and binder, the amount of paste, and $CO_2$ concentration, were considered. The experimental test results showed that the measured void ratio and compressive strength of the carbonated porous concrete exceeded minimum level stated in ACI 522 for general porous concrete. A new quantitative TG analysis for evaluating $CO_2$ uptake in AAS was proposed, and the result showed that the $CO_2$ uptake in AAS paste was approximately twice as high as that in OPC paste. The leached concentrations of heavy metals from carbonated porous concrete were below the relevant environmental criteria.

• Economic and Environmental Geology
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• v.53 no.1
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• pp.1-9
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• 2020

Magnesium silicate minerals such as serpentine [Mg₃Si₂O₅(OH)₄] have a high potential for the sequestration of CO₂; thus, their reactivity toward dissolution under CO₂-free and CO₂-containing conditions in acidic solvents is a critical process with respect to their carbonation reactions. To examine the carbonation efficiency and dissolution mechanism of serpentine, hydrothermal treatment was performed to the starting material via a modified direct aqueous carbonation process at 100 and 150℃. The serpentine dissolution experiments were conducted in H₂SO₄ solution with concentration range of 0.3-1 M and at a CO₂ partial pressure of 3 MPa. The initial pH of the solution was adjusted to 13 for the carbonation process. Under CO₂-free and CO₂-containing conditions, the carbonation efficiency increased in proportion to the concentration of H₂SO₄ and the reaction temperature. The leaching rate under CO₂-containing conditions was higher than that under CO₂-free conditions. This suggests that shows the presence of CO₂ affects the carbonation reaction. The leaching and carbonation efficiencies at 150℃ in 1 M H₂SO₄ solution under CO₂-containing conditions were 85 and 84%, respectively. The dissolution rate of Mg was higher than that of Si, such that the Mg : Si ratio of the reacted serpentine decreased from the inner part (approximately 1.5) to the outer part (less than 0.1). The resultant silica-rich layer of the reaction product ultimately changed through the Mg-depleted skeletal phase and the pseudo-serpentine phase to the amorphous silica phase. A passivating silica layer was not observed on the outer surface of the reacted serpentine.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.458-466
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• 2023

Structures in our surroundings deteriorate over time due to environmental and chemical factors, resulting in a decrease in their performance. The primary causes of degradation in concrete structures are carbonation, salt damage, and freeze-thaw cycles. Various maintenance methods exist to address these degradation issues. However, research and technological development for existing maintenance methods have been ongoing, but the accuracy and effectiveness of repair materials and techniques have not been extensively validated. Therefore, in this study, we conducted a material performance evaluation of various manufacturers' repair materials. Based on this evaluation, we applied corrosion inhibitors and epoxy, which are the methods most closely related to crack repair, to assess the durability performance against carbonation, salt damage, and freeze-thaw cycles. The results show approximately a two-fold performance improvement against carbonation and salt damage, and a 5% enhancement in repair performance against freeze-thaw cycles. Thus, it is considered effective in preventing rebar corrosion when appropriate maintenance is carried out according to environmental and chemical factors during structural repairs.

• Journal of Powder Materials
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• v.23 no.3
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• pp.221-227
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• 2016

Waste oyster shells create several serious problems; however, only some parts of them are being utilized currently. The ideal solution would be to convert the waste shells into a product that is both environmentally beneficial and economically viable. An experimental study is carried out to investigate the recycling possibilities for oyster shell waste. Bulk ceramic bodies are produced from the oyster shell powder in three sequential processes. First, the shell powder is calcined to form calcium oxide CaO, which is then slaked by a slaking reaction with water to produce calcium hydroxide $Ca(OH)_2$. Then, calcium hydroxide powder is formed by uniaxial pressing. Finally, the calcium hydroxide compact is reconverted to calcium carbonate via a carbonation reaction with carbon dioxide released from the shell powder bed during firing at $550^{\circ}C$. The bulk body obtained from waste oyster shells could be utilized as a marine structural porous material.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.41-42
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• 2011

The purpose of this study is not only fixation of carbon dioxide using the cement-saturated solution by wet carbonating reaction but also evaluate the possibility of storage technology of Carbon dioxide. wet carbonation is reaction of CO₂ injection by CO₂ reactor. As a result of experiment, the carbon dioxide is fixed, and high-purity Calcium Carbonate is eluted.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.05a
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• pp.71-72
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• 2012

The purpose of this study is not only fixation of carbon dioxide using the cement-Paste solution's calcium ion by wet carbonating reaction but also quantitatively evaluate the possibility of storage technology of Carbon dioxide. wet carbonation is reaction of CO₂ injection by CO₂ reactor. As a result of experiment, the carbon dioxide is fixed, and high-purity Calcium Carbonate is eluted.

• Corrosion Science and Technology
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• v.15 no.1
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• pp.28-37
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• 2016

Due to the increased construction of offshore concrete structures and the use of de-icing salts for the purpose of snow removal, the needs for the development of anti-corrosive concrete are increasing. To solve these problems, an evaluation of the mechanical and durability properties for concrete were conducted by mixing modified-sulfur as 0 %, 5 %, 10 %, 15 % cement weight ratio. Both strengths and the properties affecting durability such as water absorption coefficient, chloride ion permeability, accelerated carbonation resistance, rapid freezing and thawing, and chemical resistance were evaluated. All evaluations performed were according to the test specifications associated KS. The results indicate that mixing of modified-sulfur lowed chloride ion permeability and improved chemical resistance.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.1
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• pp.33-40
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• 2021

The objective of this work is to prove a possibility of void f illing through a carbonation f or the purpose of improving the quality of recycled aggregate. Carbonation can permanently immobilize CO2, which is a greenhouse gas, and thus provides additional benefit on environment. In this work, recycled fine aggregate was reacted using gaseous CO2 and supercritical CO2(scCO2) in a closed chamber, and the changes in physical properties of the recycled f ine aggregate bef ore and af ter carbonation were analyzed using the apparent density, skeletal density, pH, and FE-SEM measurements. Thereafter, a mortar specimen was prepared and a compressive strength was measured. According to the experimental results, it was found that the increase in the apparent density and the true density was higher by the reaction with scCO2, which was conducted at high temperature and high pressure compared to the reaction with gaseous CO2. In addition, the pH of the eluted water was found to have a larger initial decrease than that observed with samples from reaction by gaseous CO2. The shape and amount of calcium carbonate crystals were also found to be larger than that from gaseous CO2. The increase in compressive strength was the largest when using recycled fine aggregate reacted with scCO2. It was clear that quality improvement of recycled fine aggregate was higher with scCO2 than with gaseous CO2.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.2
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• pp.112-119
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• 2023

In this study, the variations in CO₂ uptake according to the type and amount of alkali-based activator (Ca(OH)₂, CSA) of geopolymer paste were evaluated. As the amount of activator added to the geopolymer paste increased, the fluidity of the paste is decreased and the compressive strength increased. According to the type of activator, it was confirmed that the addition of Ca(OH)₂ had a greater effect on improving the compressive strength than CSA. As a result of changes in chemical properties according to carbonation curing, the amount of C-S-H and C-A-S-H gels produced before carbonation increased as the amount of activator increased, and amount of CaCO₃ produced after carbonation increased. The reactivity of the blast furnace slag and zeolite increased due to the addition of the activator, and the reactivity tended to increase as the amount of addition increased. As a result of CO₂ uptake, 10.3 wt% when Ca(OH)₂ 10 % was added and 8.77 wt% when CSA 10 % was added was confirmed. It increased by 421 % and 388 % respectively, compared to the case where no activator was added.