• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.129-139
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• 2008

Due to uncertainty of numerous variables in durability model, a probalistic approach is increasing. Monte Carlo simulation (Level III method) is an easily accessible method, but requires a lot of repeated operations. This paper evaluated the effectiveness of First Order Second Moment method (Level II method), which is more convenient and time saving method than MCS, to predict the corrosion initiation in harbor concrete structure. Mean Value First Order Second Moment method (MV FOSM) and Advanced First Order Second Moment method (AFOSM) are applied to the error function solution of Fick's second law modeling chloride diffusion. Reliability index and failure probability based on MV FOSM and AFOSM are compared with the results by MCS. The comparison showed that AFOSM and MCS predict the similar reliability index and MV FOSM underestimates the probability of corrosion initiation by chloride attack. Also, the sensitivity of variables in durability model to corrosion initiation probability was evaluated on the basis of AFOSM. The results showed that AFOSM is a simple and efficient method to estimate the probability of corrosion initiation in harbor structures.

• Journal of Navigation and Port Research
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• v.37 no.2
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• pp.165-171
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• 2013

YoungDo bridge is the first suspension bridge in Busan which experienced several times repair and reinforcement after completion in 1934. The bridge is under demolition for extension and restoration work since 2011. The purpose of this research is to establish data base about modern concrete. The mix design of the concrete is like that cement : fine aggregate : coarse aggregate = 1 : 2 : 4 or 1 : 3 : 6 by the parts. The compressive strength is in the ranges from 50 to 55 MPa and the elastic modulus is in the ranges from 25 to 35 GPa. From the fact that the deviation is less than 10 %, considerably high quality control was conducted in those days. The carbonation depth is 5.92 cm at the bridge post and 14.3 cm at the machine room. That is why ocean environment keeps the high humidity. The diffusion coefficient of chloride ion through the pores in concrete is 1.052e-12 $m^2/s$ from the regression analysis using the experiment data. The water cement ration is estimated at approximately 35 % in case if the concrete using ordinary Portland cement.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.411-418
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• 2013

Recently, in order to reduce a damage of chloride attack and hydration heat in marine concrete structures, blended cement in mixing the marine concrete is widely used. Long term strength development is distinct in concrete with blended cement and it also has excellent resistance to chloride attack and reduction of hydration heat. However, blended cement has a characteristic of relatively low compressive strength in early age of 28 days. On the other hand, a high level of compressive strength is required in the Standard Specification for marine concrete mix design. Such concrete mix design satisfying Standard Specification is effective to chloride attack but disadvantageous for hydration heat reduction due to large quantity of binder. In this study, the material properties of marine concrete considering water-binder ratio and binder type are experimentally investigated. Through the research results, compressive strength in blended cement at the age of 56 days is similar although it has smaller compressive strength at the age of 28 days compared with result of OPC (ordinary portland cement). Even though blended cement has a large water-binder ratio and small unit of binder content, chloride ion diffusion coefficient is still small and hydration heat is also found to be reduced. For meeting the required compressive strength in Standard Specification for marine concrete at 28 days, the increased unit content of binder is needed but the increased hydration heat is also expected.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.142-154
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• 2011

This study predicted the probability of corrosion initiation of reinforced concrete tunnel boxes structures using the Monte Carlo Simulation. For the inner wall and outer wall in the tunnel boxes, exposed to airborne chloride ion and seawater directly respectively, statistical values of parameters like diffusion coefficient D, surface chloride content $C_s$, cover depth c, and the chloride threshold level $C_{lim}$ were examined from experiment or literature review. Their average values accounted for $3.77{\times}10^{-12}m^2/s$, 3.0% by weight of cement, 94.7mm and 45.5mm for outer wall and inner wall, respectively, and 0.69% by weight of cement for D, $C_s$, c, and $C_{lim}$, respectively. With these parametric values, the distribution of chloride contents at rebar with time and the probability of corrosion initiation of the tunnel boxes, inner wall and outer wall, was examined by considering time dependency of chloride transport. From the examination, the histogram of chloride contents at rebar is closer to a gamma distribution, and the mean value increases with time, while the coefficient of variance decreases with time. It was found that the probability of corrosion initiation and the time to corrosion were dependent on the time dependency of chloride transport. Time independent model predicted time to corrosion initiation of inner wall and outer wall as 8 and 12 years, respectively, while 178 and 283 years of time to corrosion was calculated by time dependent model for inner wall and outer wall, respectively. For time independent model, the probability of corrosion at 100 years of exposure for inner wall and outer wall was ranged 59.5 and 95.5%, respectively, while time dependent model indicated 2.9 and 0.2% of the probability corrosion, respectively. Finally, impact of $C_{lim}$, including values specified in current codes, on the probability of corrosion initiation and corrosion free life is discussed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.2
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• pp.136-143
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• 2013

In the sewage structures and wastewater facilities, concrete is exposed to hydrogen sulfide ($H_2S$) which acts as an acid material in a solution, and a strongly acidic sulfate ion ($SO{_4}^{-2}$) is generated by a sulfuric bacteria. Hence, a degradation of concrete with biochemical corrosion would be accelerated. Finally, durability of concrete and concrete structures may be greatly reduced. In this study, in order to remove the hydrogen sulfide which is used by the sulfuric bacteria organic-biologically, the antibiotic metal and metallic salt powders were mixed to concrete, and a suppressing performance of the sulfate ion was assessed. For the sulfuric acid bacteria, a comparative evaluation of antimicrobial performance on neutralized concrete specimens were carried out, also by a rapid chloride penetration test, chloride penetration depths and diffusion coefficients were measured for antibiotic concrete in accordance with the amount of metal and metallic salt-based antibacterial agents. Eventually, by an observation of the biochemical state of the surface of concrete specimens exposed outdoors, the performance and applicability of antibiotic concrete were confirmed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.127-134
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• 2022

In this study, RCPTs (Rapid Chloride Penetration Test) were performed for fly ash concrete with curing age of 4 ~ 6 years. The concrete mixtures were prepared with 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%), and the improved passed charges of chloride ion behavior were quantitatively analyzed. Additionally, the results were trained through the univariate time series models consisted of GRU (Gated Recurrent Unit) algorithm and those from the models were evaluated. As the result of the RCPT, fly ash concrete showed the reduced passed charges with period and an more improved resistance to chloride penetration than OPC concrete. At the final evaluation period (6 years), fly ash concrete showed 'Very low' grade in all W/B (water to binder) ratio, however OPC concrete showed 'Moderate' grade in the condition with the highest W/B ratio (0.47). The adopted algorithm of GRU for this study can analyze time series data and has the advantage like operation efficiency. The deep learning model with 4 hidden layers was designed, and it provided a reasonable prediction results of passed charge. The deep learning model from this study has a limitation of single consideration of a univariate time series characteristic, but it is in the developing process of providing various characteristics of concrete like strength and diffusion coefficient through additional studies.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.305-311
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• 2010

The industrial by-product market has increased at a geometric rate worldwide with the rapid economic growth. At present time, conventional disposal methods of industrial by-products in Korea including landfill, incineration and storage already have reached their limits. In this study, the industrial by-products such as fly ash and silicafume were used as mineral admixtures, which are commonly added to concrete mix to inhance the economic efficiency, long-term strength and durability of concrete, to determine the optimized mix proportion of high performance shotcrete. Through the series of tests (compressive strength test, accelerated chloride ion penetration test, measurement of chloride diffusion coefficient). The results of the study showed that the proposed mix proportions satisfied the requirements of domestic as well as international guidelines for shotcrete, with a higher durability than the existing shotcrete.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.679-686
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• 2018

Reverse osmosis (RO) concentration of sodium chloride, sodium acetate, and sodium citrate solutions has been performed by polyamide RO membrane. Concentration polarization phenomena was also studied by changing pressure, solute kinds, and initial solution concentration. Pressure effect on permeation flux was that the increase of flux was accompanied by the increase of pressure. Flux increase was observed by the decrease of initial solution concentration. Surface concentration on the RO membrane increases and so flux declines due to the concentration polarization. In the later phase of concentration, concentration polarization effect was decreased by the back diffusion of solute from the polariztion layer. In case of sodium citrate, its large ion size and charge density resulted in the discrepancy between theory and experimental data of concentration polarization. It may be due to electric repulsion on the membrane surface.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.857-868
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• 2005

This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.160-163
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• 2004

In domestic, various repair materials and method systems to keep up with these reinforced concrete deteriorated due to salt damage, carbonation, chemical decay et. developed and applied. However, on-site quality control of various repair materials and method systems isn't achieved desirably because it is depend completely on a men of experience' opinions above all else regardless of various on-site environments. In this background, mock up test with due regard to real on-site environments was performed to secure fundamental data for establishment of desirable on-site quality control. Mock up test using repair mortar analyzed from angles of construction methods, mechanical spraying pressures, W/M. Construction methods were designed manpower method and spraying method, spraying pressures were designed 32, 42, 52 psi, W/M were designed 14.4, 15.4, $16.4\%$. And compressive strength, Chloride ion diffusion coefficient, bond strength, SEM. of mock up test specimens were evaluated. In conclusion, we confirmed excellency of mechanical spraying pressures, fined extremely excellency of condition of spraying pressure 42 ps, W/M $14.4\%$ within this study. therefore the results of this study will be useful to provide fundamental data for establishment of desirable on-site quality control.