• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.122-129
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• 2019

The movement of deterioration agents such as a chloride ion, etc. in concrete varies with loading conditions and micro-structure developed by age effect. In this paper, the carbonation behavior by accelerated carbonation test is evaluated considering curing periods(28 days, 91 days, and 365 days) and loading conditions. Carbonation velocity coefficients are obtained referred to KS F 2584. In the control case without loading condition, carbonation velocity coefficient of 91 days decreases to 50.0 % level and that of 365 days decreases to 44.8 % level than that of 28 days curing condition. In 28 curing days, carbonation velocity coefficients changed level of 103.9 ~ 108.8 % in tensile region and 91.9~104.6 % in compressive region by loading conditions. Carbonation velocity coefficients in the 30 % and 60 % tensile loading case at 28 days decreases to 47.3 % and 52.5 % level compared to control case after 1 year. Furthermore, 45.8 % and 44.9 % level of carbonation velocity coefficients are evaluated for 30 % and 60 % compressive loading conditions compared to control case after 1 year. Carbonation velocity coefficient decreases in the 30 % compressive loading level due to effective pore compaction and it increases afterwards due to micro-cracking. In the tensile loading condition, unlike the behavior of compressive region, it linearly increases with increasing loading level.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.3
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• pp.246-253
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• 2024

When concrete with slag powder or fly ash is under an accelerated carbonation test at early age, a very complicated carbonation behavior occurs since several reactions covering cement hydration, pozzolanic reaction, and carbonation reaction occu simultaneously. In particular, fine and coarse aggregates with poor quality were used, the trend with strength development and carbonation behavior was not clear. In this study, concrete samples with three design strength grade(24 MPa, 27 MPa, and 30 MPa) were manufactured with different aggregates site(A, B, and C). Compressive strength test were performed considering curing ages(7 and 28 days), and the accelerated carbonation tests were performed for 8 weeks for evaluating carbonation rate. The relationship between compressive strength and carbonation rate was analyzed considering mix properties and the aggregate site conditions. In addition, the minimum cover depth satisfying intended service life was obtained through carbonation design based on Domestic Design Code, and the necessities for improving design parameters (direction coefficient and effective water-binder ratio) were suggested.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.259-266
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• 2018

In the work, the carbonation behavior and strength characteristics in cold-joint concrete are evaluated for OPC(Ordinary Portland Cement) and GGBFS(Ground Granulated Blast Furnace Slag)concrete considering three levels of curing age (28, 91 and 365 days). The compressive strength in GGBFS concrete is level of 86% of OPC concrete at the 91 days of curing period, but is level of 107% at 365 curing days due to hydration reaction. Carbonation velocities in both OPC and GGBFS concrete significantly decease after 91 curing days. The effect of cold joint on carbonation is evaluated to be small in GGBFS concrete. The increasing ratios of carbonation velocity in cold joint are 1.06 and 1.33 for 28-day and 365-day curing condition, respectively. However they decreases to 1.08 and 1.04 for GGBFS concrete for the same curing conditions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.4
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• pp.220-227
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• 2021

PCT (Power Cable Tunnel) and UT (Utility Tunnel), which are non-transport underground infrastructures, are mostly RC (Reinforced Concrete) structures, and their durability decreases due to the deterioration caused by carbonation over time. In particular, since the rate of carbonation varies by use and region, a predictive model based on actual carbonation data is required for individual maintenance. In this study, a carbonation prediction model was developed for non-transport underground infrastructures, such as PCT and UT. A carbonation prediction model was developed using multiple regression analysis and deep neural network techniques based on the actual data obtained from a safety inspection. The structures, region, measurement location, construction method, measurement member, and concrete strength were selected as independent variables to determine the dependent variable carbonation rate coefficient in multiple regression analysis. The adjusted coefficient of determination (Ra2) of the multiple regression model was found to be 0.67. The coefficient of determination (R2) of the model for predicting the carbonation of non-transport underground infrastructures using a deep neural network was 0.82, which was superior to the comparative prediction model. These results are expected to help determine the optimal timing for repair on carbonation and preventive maintenance methodology for PCT and UT.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.209-217
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• 2010

Recently, some mathematical models for the prediction on progress of carbonation of concrete were reported. These models take account for $CO_2$ diffusion and chemical reaction between $Ca(OH)_2$ and $CO_2$. Based on the assumption that $CO_2$ diffuses in the carbonation zone and reacts with $Ca(OH)_2$ at the outer face of carbonation zone and non-carbonation zone. In this study, a mathematical model to predict the progress of carbonation of concrete has been established based on the reducing concentration of $Ca(OH)_2$ in the carbonation progress zone, where $Ca(OH)_2$ reacts with $CO_2$ and $Ca(OH)_2$ and $CaCO_3$ coexist. Also, the prediction model of carbonation progress rate of concrete using the air permeability coefficient regarding to $CO_2$ diffusion is developed. As a result of this study, an expression, the model equation is obtained for the prediction of carbonation based on the time and interaction velocity between $CO_2$ and Ca(OH)$_2$ dependent air permeability coefficient. The prediction by the model satisfied the experimental data of the accelerated carbonation for painted concrete. Consequently, the model can predict the rate of carbonation and the potential service life of concrete structure exposed to atmosphere.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.301-302
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• 2009

Uncertainties in carbonation process of concrete structures are treated by probability-based durability analysis for carbonation using Monte Carlo simulation technique. The results requires the minimum cover thickness of 53mm for 10% of corrosion probability under 4mm/$year^{0.5}$ of carbonation coefficient. The more researches on statistical properties of design variables may give reliable durability analysis/design methods for carbonation of concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.163-170
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• 2008

The carbonation velocity is produced an effect on carbon dioxide($CO_2$) density of surrounding near structures, the concrete quality and types of structures and this study was accomplished to draw a conclusion for estimated formula of carbonation velocity coefficient with various factors by the concrete quality on the base of the data of the durability surveyed in Korea. From the results of analysis of carbonation velocity, the followings were appeared. It is analyzed that carbonation velocity of the structures under urban area is 1.5 times faster than the rural area in the bridges case and it is 2.5 times faster than the rural area in the tunnels case. And the order of carbonation velocity of the structures under urban area is the buildings, the tunnels, the bridges and they are evaluated to progress about 2.7 times and 1.3 times faster than the bridges. In the rural area, the bridges are evaluated to progress about 1.3 times faster than the tunnels and it is analyzed that the carbonation velocity of the upper structures of the bridges under urban area is about 1.3 times faster than lower structures. The results which is compared to estimated formula of carbonation velocity coefficient of Kishitani equation which is generally applied for convert compressive strength into W/C ratios, most of those velocity of structures is faster than the results of Kishitani equation.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.449-455
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• 2009

The increase of industrial carbonic dioxide emissions has accelerated the carbonation of reinforced concrete structures, which drops off their durability. Although advanced countries have already taken safety control measures against the carbonation of RC structures, it is still difficult now to accurately predict the actual carbonation depth. Additionally, it requires much time and efforts. Recently, it is possible to get the data more rapidly through accelerated carbonation test with the $CO_2$ concentration of 100%. In this paper, the carbonation test results obtained by two test methods such as the normal carbonation test method and the accelerated carbonation test method, were compared to investigate the carbonation characteristics of fly ash concrete. The accelerated carbonation test on concrete specimens with the pre-curing age of 180 days was also carried out to examine the carbonation characteristics of fly ash concrete at long-term age. Consequently, fly ash concrete at early age was vulnerable to carbonation and however, its carbonation resistance at long-term ages was improved compared with OPC concrete.

• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.235-243
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• 2017

Carbonation of concrete is being occurred due to interaction of atmospheric carbon dioxide with hydroxides. Reinforce concrete (RC) structure is getting collapse or accident due to corrosion of embedded steel rebar. The maintenance of reinforced concrete structure recently has the attention of researchers regarding durability of structure and its importance day by day is increasing. In order to study the carbonation progress of pre-repaired concrete, present study was carried out to measure the carbonation velocity for different repair materials up to 100% of carbonation. The obtained results have predicted the carbonation progress of repair materials in service condition. These results have been verified by FEM and FDM analysis. As a result, the carbonation depth can be predicted by using the carbonation prediction formula after the repair, and the analytical and the experimental values are almost similar when the initial $Ca(OH)_2$ concentration is assumed to be 40%.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.501-504
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• 2008

A concrete carbonation model has been constructed that takes account of the diffusion of carbon dioxide through a coating and reaction with calcium hydroxide, and this model has been validated by an accelerated carbonation experiment. (1) By using values for the coatings calculated on the basis of a diffusion.permeation theory as input data for the analysis of diffusion.reaction carbonation in an unsteady state, the effect of the coatings in reducing carbonation can be represented with high accuracy. (2) Through a sensitivity analysis of the diffusion.reaction carbonation model and the experimental results, we found that the diffusion coefficient of calcium hydroxide shows a high interrelationship at 1e-12($m^2/s$). The reaction rate constant for carbonation shows a high interrelationship at 5e-5($m^3/mol/s$).