• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.145-153
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• 2013

Recently, accelerated chloride diffusion coefficients are used for an evaluation of chloride behavior. Similar as apparent diffusion coefficients, accelerated diffusion coefficients decrease with time. In this study, decrease in diffusion coefficient with time is simulated with porosity. Utilizing DUCOM-program, porosities from 15 mix proportions are obtained and diffusion coefficients are modelled with regression analysis of porosity for 270 days. Considering non-linear binding capacity which means the relation between free and bound chloride ion, chloride behavior in high performance concrete is evaluated. Through utilizing the previous test results for concrete under chlorides for 180 days, the applicability of the proposed technique is verified. The proposed technique is evaluated to reasonably predict the chloride behavior in concrete with various w/c (water to cement) ratios and mineral admixtures (GGBFS and FA). It is also shown that decrease in chloride diffusion should be considered for chloride prediction in concrete with mineral admixture since it has very clear decrease in diffusivity with time.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.83-91
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• 2015

With varying conditions of concrete surface, induced chloride contents are changed and this is a key parameter for steel corrosion and service life in RC (Reinforced Concrete) structures. Many surface enhancement techniques using impregnation have been developed, however the evaluation techniques for chloride behavior through doubly layered media and time-dependent diffusion are rarely proposed. This paper presents an analysis technique considering double-layer concrete and time-dependent diffusion behavior, and the results are compared with those from the previous test results through reverse analysis. The chloride profiles from the surface-impregnated concrete exposed to atmospheric, tidal, submerged zone for 2 years are adopted. Furthermore surface chloride contents and diffusion coefficients are obtained, and are compared with those from Life365. Through consideration of time effect, the relative error decreases from 0.28 to 0.20 in atmospheric, 0.29 to 0.11 in tidal, and 0.54 to 0.40 in submerged zone, respectively, which shows more reasonable results. Utilizing the diffusion coefficients from Life365, relative errors increases and it needs deeper penetration depth (e) and lower diffusion coefficient ratio ($D_1/D_2$) due to higher diffusion coefficient.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.259-268
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• 2016

The service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack can be classified into deterministic and probabilistic method, and it significantly varies with design parameters. The present work derives PDF (Probability of Durability Failure) and the related service life considering time-dependent diffusion coefficient and internal parameters such as reference diffusion coefficient, critical chloride content, and time-exponent. When critical chloride content increases to 133.3%, the changing ratios of service life are 134.0~145.4% for deterministic method and 149.2%~152.5% for probabilistic method, respectively. In the case of increasing time-exponent to 200%, they increase to 323.8% for deterministic method and 346.0% for probabilistic method. Through adopting time-diffusion coefficient for probabilistic method, reasonable service life evaluation can be achieved, and it is also verified that increasing time-exponent through mineral admixture is very effective to extension of service life in RC structure.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.8-15
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• 2019

When RC(Reinforced Concrete) structures are exposed to harsh environment, deterioration phenomenon occurs, and the corrosion in rebar due to chloride intrusion is known as representative deterioration, so called chloride attack. In this paper, chloride resistance performance of 2 years aged concrete is evaluated considering 3 levels of water to binder ratio(0.37, 0.42, and 0.47) and 2 levels of substitution ratio of fly ash(0% and 30%). Accelerated chloride diffusion coefficient tests referred to Tang's method, total passed charge tests referred to ASTM C 1202, and compressive strength tests referred to KS F 2405 are performed. With adaptation of the previous test results and the results from this study, time-dependent chloride diffusion characteristics are analyzed for each concrete. The FA(Fly Ash) concrete has higher chloride resistance performance than OPC(Ordinary Portland Cement) concrete. According to the evaluation standard of ASTM C 1202, the FA concrete has "Moderate" grade after 49 days while OPC concrete does "Moderate" grade after 365 days. As the results of time-parameter for chloride diffusion, OPC concrete and FA concrete show the decreasing behavior of time-parameters with increasing water to binder ratio. Also, FA concrete has 1.57~2.74 times of time-parameter than OPC concrete. That's cause is thought that the time-parameter indicates the gradient of decreasing of diffusion coefficient. FA concrete has higher time-parameters than OPC concrete by pozzolanic reaction of FA.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.715-726
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• 2012

Since strength and diffusion coefficient of concrete, representative concrete properties that in change with age, the time effect must be considered in the analysis of chloride penetration. In this study, an evaluation of correlation between accelerated diffusion coefficient, apparent diffusion coefficient, and compressive strength in high performance concrete with various mineral admixtures such as ground granulated blast furnace slag, fly ash, and silica fume was performed. For this work, thirty mix proportions were prepared. Accelerated diffusion coefficients at the age of 28, 91, 180, and 270 days were evaluated. For apparent diffusion coefficient, submerging test for 6 months was performed. For evaluation of compressive strength with ages, the compressive strength test was carried out at an age of 7, 28, 91, 180 days. The results of accelerated diffusion coefficient, apparent diffusion coefficient, and strength were compared, and the correlation was analyzed considering time dependency. From this study, linear relationship between accelerated diffusion and apparent diffusion coefficient were obtained regardless of concrete age. The linear relations were also observed in strength-accelerated diffusion coefficient and strength-apparent diffusion coefficient regardless of concrete age.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.46-52
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• 2017

Recently durability design based on deterministic or probabilistic method has been attempted since service life evaluation in RC(Reinforced Concrete) structure exposed to chloride attack is important. The deterministic durability design contains a reasonable method with time effect on surface chloride content and diffusion coefficient, however the probabilistic design procedure has no consideration of time effect on both. In the paper, a technique on PDF(Probability of Durability Failure) evaluation is proposed considering time effect on diffusion and surface chloride content through equivalent surface chloride content which has same induced chloride content within a given period and cover depth. With varying period to built-up from 10 to 30 years and maximum surface chloride content from $5.0kg/m^3$ to $10.0kg/m^3$, the changing PDF and the related service life are derived. The proposed method can be reasonably applied to actual durability design with preventing conservative design parameters and considering the same analysis conditions of the deterministic method.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.149-156
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• 2016

The service life in RC (Reinforced Concrete) is very important and it is usually obtained through deterministic method based on Fick's 2nd law and probabilistic method. This paper presents an evaluation of $P_{df}$(durability failure probability) and the related service life considering time-dependent behaviors in chloride diffusion and surface chloride content. For the work, field investigation is performed for RC structures exposed to chloride attack for 3.5~4.5years, focusing tidal zone (6.0 m) and sea shore (9.0 m), respectively. Random variables like cover depth, chloride diffusion coefficient, and surface chloride content are obtained, and $P_{df}$ and the service life are evaluated. Unlike the results from deterministic method using LIFE 365, probabilistic method with time effects on diffusion and surface chloride shows a relatively rapid change in the result, which is a significant reductions of service life in the case with low surface chloride content. For probabilistic evaluation of durability, high surface chloride content over $10.0kg/m^3$ is required and reasonable service life can be derived with consideration of time-dependent diffusion coefficient.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.481-490
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• 2012

Evaluation of chloride penetration is very important, because induced chloride ion causes corrosion in embedded steel. Diffusion coefficient obtained from rapid chloride penetration test is currently used, however this method cannot provide a correct prediction of chloride content since it shows only ion migration velocity in electrical field. Apparent diffusion coefficient of chloride ion based on simple Fick's Law can provide a total chloride penetration magnitude to engineers. This study proposes an analysis technique to predict chloride penetration using apparent diffusion coefficient of chloride ion from neural network (NN) algorithm and time-dependent diffusion phenomena. For this work, thirty mix proportions with the related diffusion coefficients are studied. The components of mix proportions such as w/b ratio, unit content of cement, slag, fly ash, silica fume, and fine/coarse aggregate are selected as neurons, then learning for apparent diffusion coefficient is trained. Considering time-dependent diffusion coefficient based on Fick's Law, the technique for chloride penetration analysis is proposed. The applicability of the technique is verified through test results from short, long term submerged test, and field investigations. The proposed technique can be improved through NN learning-training based on the acquisition of various mix proportions and the related diffusion coefficients of chloride ion.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.52-59
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• 2018

To control chloride attacks which is a representative deterioration in RC(Reinforced Concrete) structures, many studies have been conducted. Above all, a method using mineral admixture was known to be effective for corrosion protection. In this study, durability test about chloride attacks was carried out for concrete specimens containing FA(Fly Ash)-representative concrete mineral admixture and OPC concrete specimens considering 3 different levels of W/B(Water to Binder). Accelerated chloride diffusion coefficient tests referred to Tang's method, total passed charge tests referred to ASTM C 1202, and compressive strength tests based on KS F 2405 were performed at each target age day. Also, based on previous studies of 28 days, time-parameter which is a key parameter for diffusion behavior is evaluated and its relations with compressive strength at the age of 365 days is evaluated. After the age of 49 days, chloride resistance of FA concrete is much improved than that of OPC concrete, which arose out of stable hydrates due to pozzolan reaction of fly ash. Time-parameter of FA concrete is evaluated to be about 1.5 times larger than that of OPC concrete. Also, time-parameter of FA concrete has a linearly decreasing relation while that of OPC concrete has a linearly increasing relation with compressive strength development.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.545-548
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• 2008

As the corrosion of reinforcing bar in concrete structures exposed to chloride attack is one of main factors to determine the remaining service life, marine concrete structures have to be designed to protect the chloride penetration. Among the durability design methods such as deterministic method and probabilistic method, design method based on the probabilistic theory has been widely studied. However, the most essential material, data of the material properties related to chloride diffusion, are still insufficient. In this paper, the probabilistic distribution of chloride diffusion coefficients and aging coefficients are derived by the experiment and analysis for the chloride coefficients of concrete containing pozzolans, which are generally used in marine structures.