• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.365-371
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• 2009

It is time-consuming to estimate chloride diffusivity of concrete by concentration difference test. For the reason chloride diffusivity of concrete is mainly tested by electrically accelerated method, which is accelerating the movement of chloride ion by potential difference. In this study, portland cement concrete and concrete containing with ground granulated blast-furnace slag (40 and 60% of cement by weight) with water-cementitious material ratio 40, 45, 50 and 60% were manufactured. To compare with chloride diffusivity calculated from the electrically accelerated test and immersed test in artifical seawater, chloride diffusivity tests were conducted. From the results of regression analysis, regression equation between accelerated chloride diffusivity and immersed chloride diffusivity was linear function. And the determinant coefficient was 0.96 for linear equation.

• Journal of the Korea Concrete Institute
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• v.16 no.2 s.80
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• pp.261-268
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• 2004

Corrosion of reinforcement is the main cause of damage and early failure of reinforced concrete structures. The corrosion is mainly progressed by the chloride ingress. In this paper, an experimental study is executed to investigate the effect of concrete properties and testing methods on the coefficients of chloride diffusion. Also, it is surveyed the relationship between total chloride and free chloride in concrete. According to this experiment results, W/C ratio and testing method affect chloride diffusion coefficient of concrete. As W/C ratio is increased, diffusion coefficient in concrete is also increased. Diffusion coefficient obtained by each testing method show the different values, respectively. The model equation of diffusion coefficient with W/C ratio is proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.44-49
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• 2016

Among the deteriorating agents, chloride ion is reported to be one of the most harmful ions due to its rapid diffusion and direct effect on steel corrosion. Cold joint which occurs in mass concrete placing is vulnerable to shear resistance and more severe deterioration. The paper presents an quantitative evaluation of chloride diffusion coefficient in OPC(Ordinary Portland Cement) and GGBFS(Ground Granulated Blast Furnace Slag) concrete containing cold joint. GGBFS concrete shows $6.6{\times}10^{-12}m^2/sec$ which is almost 30% level of OPC concrete results and the trend is repeated in the case of cold joint concrete. Compared with OPC concrete, GGBFS concrete is evaluated to have better resistance to chloride penetration, showing 0.30 times of chloride diffusion coefficient in concrete without cold joint 0.39 times with cold joint, respectively.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.1-7
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• 2017

Concrete behavior in early-age is changing due to hydration reaction with time, and a resistance to chloride attack and strength development are different characterized. In the present work, changing strength and resistance to chloride attack are evaluated with ages from 28 days to 6 months. For the purpose, strength, diffusion coefficient, and passed charge are evaluated for normal concrete with 3 different mix proportions considering 28-day and 6-month curing conditions. With increasing concrete age, the changing ratio of strength falls on the level of 135.3~138.3%, while diffusion coefficient and passed charge shows 41.8%~51.1% and 53.6%~70.0%, respectively. The results of chloride diffusion coefficient and passed charge show relatively similar changing ratios since they are much dependent on the chloride migration velocity in electrical field. The changing ratios in chloride behaviors are evaluated to be much larger than those in compressive strength since the ion transport mechanism is proportional to not porosity but square of porosity.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.319-326
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• 2004

This paper investigates the effect of the concrete containing mineral admixtures(pozzolanic materials such as fly-ash, ground granulated blast-furnace slag, silica fume and meta kaolin) on the resistance properties to chloride ion invasion. The purposed testing procedure was applied to the concrete replaced mineral admixtures for 3${\~}$4 replacement ratios under water-binder ratios ranged from 0.40 to 0.55. For the electro-migration test, Tang and Nilsson's method was used to estimate the diffusion coefficient of chloride ion. As a results, the water-binder ratios, kinds of mineral admixtures and replacement ratios, water curing periods had a great effect on the diffusion coefficient of chloride ion, and the optimal replacement ratios had a limitation for each mineral admixtures. Also, the use of mineral admixtures by mass(replacement of OPC) enhance the resistance ability against chloride penetration compared with the plain concrete. The compressive strength was shown related to the diffusion coefficient of chloride ion, the compressive strength increases with the diffusion coefficient of chloride ion decreasing. Below the 50 MPa, the variation of diffusion coefficient of concrete replaced mineral admixtures was bigger than that of plain concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.30-36
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• 2019

In order to evaluate service life of RC (Reinforced Concrete) structures exposed to chloride attack, chloride penetration analysis is required referred to the chloride diffusion coefficient from the actual mix proportions. In this work, accelerated diffusion coefficients are obtained from NT BUILD 492 and ASTM C 1202 and the related apparent diffusion coefficients are derived via the previously proposed relationship for RC structures near to sea shore. Considering the properties of the mix proportions and the most conservative analysis conditions like critical and surface chloride contents, service lifes in column and exterior wall member are evaluated through conventional program LIFE 365 ver.2. The different built-up period of 10 and 15 years has no significant effect on service life. The results from mix proportions with slag show longer than 75 years of service life with the help of higher time dependent parameter and lower initial 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.23 no.6
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• pp.9-17
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• 2019

Cement hydrates and the related characteristics change with ages, and the behaviors are much related with chloride diffusion. In this work, 30% replacement ratio with FA(Fly Ash) and GGBFS(Ground Granulated Blast Furnace Slag) are considered for concrete with three levels of W/B (Water to Binder ratio) and 2 years of curing period. Chloride diffusion coefficients from accelerated condition are obtained at 5 measurement period (28days, 56days, 180days, 365days, and 730days), and the results are compared with porosity, binding capacity, and permeability from program-DUCOM. The similar changing pattern between chloride diffusion and permeability is observed since permeability is proportional to the square of porosity. Curing period is grouped into 4 periods and the changing ratios are investigated. Cement hydrate characteristics such as porosity, permeability, and diffusion coefficient are dominantly changed at the early ages (28~56 days), and diffusion coefficient in OPC concrete with low W/B continuously changes to 180days.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.2
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• pp.18-27
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• 2022

In this study, the time-dependent chloride ingress behavior in GGBFS concrete was evaluated considering marine exposure conditions and the properties of concrete mixtures. The concrete mixture for this study had 3 levels of water to binder ratio and the substitution rate of GGBFS, and outdoor exposure tests were performed considering submerged area, tidal area, and splash area. According to the evaluation results of diffusion coefficient considering properties of concrete mixtures, as the substitution rate of GGBFS increased, the decreasing rate of the diffusion coefficient decreased based on exposure periods of 730 days(2 years). As the evaluation result of the diffusion behavior according to the marine exposure conditions, the diffusion coefficient was evaluated in the order of submerged area, tidal area, and splash area. In tidal area, a relatively high diffusion coefficient was evaluated due to the repetition of wet and dry seawater. In this study, the effects of GGBFS substitution rate on the decreasing behavior of apparent chloride diffusion coefficient was analyzed in consideration of exposure conditions and periods. Linear regression analysis was performed with apparent chloride diffusion coefficient as output value and GGBFS substitution rate as input value. After 730 days of exposure, the effect of GGBFS on diffusion coefficient was significantly reduced. Even for OPC concrete, after 730 days, the diffusion coefficient was as low as that of GGBFS concrete, so the gradient of the regression equation decreased significantly. It is thought that improved durability performance for chloride ingress can be secured before 730 days through the use of GGBFS.