• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.1
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• pp.19-32
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• 2024

An investigation into the detailed safety diagnosis report indicates that domestic highway bridges mainly suffer from defects, deterioration, and damage due to physical forces. In particular, deterioration is an inevitable damage that occurs due to various environmental and external factors over time. In particular, bridge deck is very vulnerable to cracks, which occur along with various types of damages such as rebar corrosion and surface delamination. Thus, this study evaluates a correlation between heterogeneous damage and deterioration environment and then identifies the main causes of such heterogeneous damage. After all, a bridge heterogeneous damage prediction model was developed using random forests to determine the top five factors contributing to the occurrence of the heterogeneous damage. The results of the study would serve as a basic data for estimating bridge maintenance and budget.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.73-81
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• 2022

Recently, as the service life of structures increased, the load-carrying capacity of deteriorated reinforced concrete, where corrosion of reinforcing bars occurs due to various causes, is frequently decreased. In order to address this problem, many studies on the bond characteristic of FRP (Fiber Reinforced Polymer) bars with corrosion resistance, light weight and high tensile strength have been conducted, however there are not many studies on the bond characteristic of grid-typed CFRP embedded in concrete. Therefore, in order to evaluate the bond characteristics of grid-typed CFRP and its usability as a substitute for steel rebar, a pull-out test is performed using the longitudinal bond length and transverse grid length of the grid-typed CFRP as variables. Through the pull-out test, the bond load-slip curve of the grid-typed CFRP is derived, and the bond behavior is analyzed. The total bond load equation is proposed as the sum of the bond force of the longitudinal bond length and the shear force of the grid in the transverse direction. Also, expressing the area of the bond load-slip curve as total work, the change in dissipated energy with respect to the slip is analyzed to examine the effect of the tranverse grid on the bond force.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.569-577
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• 2021

CFRP(Carbon Fiber Reinforced Plastic) can maintain the same strength even if the diameter is reduced by about one - third, and the weight is about one - twentieth of that of the deformed reinforcing bars that have been used in the construction industry. In particular, it is resistant to corrosion, which is the weakest part of reinf orcing bars, and there is no concern that it will deteriorate over time, It is light and durable, so transportation costs are low and it is convenient for high-rise buildings. This paper experimentally clarifies the adhesive properties of CFRP and clarifies its behavior. That is, bond strength test was conducted with the directness of CFRP and the strength of concrete as experimental variables, and the bond mechanism was clarified experimentally. Furthermore, based on the experimental results, we constructed the bond stress-slip-strain relationship of CFRP compared to the existing deformed reinforcing bars.

• Computers and Concrete
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• v.32 no.3
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• pp.247-261
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• 2023

Due to the non-uniform distribution of meso-structure, the diffusion of chloride ions in concrete show the characteristics of characteristics of randomness and fuzziness, which leads to the non-uniform distribution of chloride ions and the non-uniform corrosion of steel rebar in concrete. This phenomenon is supposed as the main reason causing the uncertainty of the bearing capacity deterioration of reinforced concrete structures. In order to analyze and predict the durability of reinforced concrete structures under chloride environment, the random features of chloride ions transport in concrete were studied in this research from in situ meso-structure of concrete. Based on X-ray CT technology, the spatial distribution of coarse aggregates and pores were recognized and extracted from a cylinder concrete specimen. In considering the influence of ITZ, the in situ mesostructure of concrete specimen was reconstructed to conduct a numerical simulation on the diffusion of chloride ions in concrete, which was verified through electronic microprobe technology. Then a stochastic study was performed to investigate the distribution of chloride ions concentration in space and time. The research indicates that the influence of coarse aggregate on chloride ions diffusion is the synthetic action of tortuosity and ITZ effect. The spatial distribution of coarse aggregates and pores is the main reason leading to the non-uniform distribution of chloride ions both in spatial and time scale. The chloride ions concentration under a certain time and the time under a certain concentration both satisfy the Lognormal distribution, which are accepted by Kolmogorov-Smirnov test and Chi-square test. This research provides an efficient method for obtain mass stochastic data from limited but representative samples, which lays a solid foundation for the investigation on the service properties of reinforced concrete structures.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.147-160
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• 2008

This paper presents the results of full-scale loading tests performed on 54 passive anchors and 4 group anchored footings grouted to various lengths at several sites in Korea. The test results, the failure mechanisms as well as uplift capacities of rock anchors depend mostly on rock type and quality, embedded fixed length, properties of the discontinuities, and the strength of rebar. Anchors in poor quality rocks generally fail along the grout/rock interfaces when their depths are very shallow (a fixed length of less than 1 m). However, even in such poor rocks, we can induce a more favorable mode of rock pull-up failure by increasing the fixed length of the anchors. On the other hand, anchors in good quality rocks show rock pull-up failures with high uplift resistance even when they are embedded at a shallow depth. Laboratory test results revealed that a form of progressive failure usually occurs starting near the upper surface of the grout, and then progresses downward. The ultimate tendon-grout bond strength was measured from $18{\sim}25%$ of unconfined compressive strength of grout. One of the important findings from these tests is that the measured strains along the corrosion protection sheath were so small that practically the reduction of bond strength by the presence of sheath would be negligible. Based on test results, the main parameters governing the uplift capacity of the rock anchor system were determined. By evaluation of the ultimate uplift capacity of anchor foundations in a wide range of in situ rock masses, rock classification suitable for a transmission tower foundation was developed. Finally, a very simple and economical design procedure is proposed for rock anchor foundations subjected to uplift tensile loads.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.118-125
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• 2017

In this study, we examined the bond performance of FRP Hybrid Bars. FRP Hybrid Bars are developed by wrapping glass fibers on the outside of deformed steel rebars to solve the corrosion problem. The surface of the FRP Hybrid Bars was coated with resin and silica sand to enhance its adhesion bonding performance with concrete. Various parameters, such as the resin type, viscosity, and size of the silica sand, were selected in order to find the optimal surface condition of the FRP Hybrid Bars. For the bonding test, FRP Hybrid Bars were embedded in a concrete block with a size of 200 mm3 and the maximum load and slip were measured at the interface between the FRP Hybrid Bar and concrete through the pull-out test. From the experimental results, the maximum load and bond strength were calculated as a function of each experimental variable and the resin type, viscosity and size of the silica sand giving rise to the optimal bond performance were evaluated. The maximum bond strength of the specimen using epoxy resin and No. 5 silica sand was about 35% higher than that of the deformed rebar.

• Journal of the Korea Institute of Building Construction
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• v.18 no.3
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• pp.203-210
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• 2018

Corrosion of the rebar is one of the main factors affecting the durability of reinforced concrete in the world which lead to the failure of the reinforced concrete structures. In this research, a new method of fixing $CO_2$ is practiced to improve the carbonation resistance of the concrete. Brucite($Mg(OH)_2$), a kind of common $CO_2$ fixation materials, was added into ordinary Portland cement paste. Samples containing 0%, 5%, 10%, and 15% $Mg(OH)_2$ were exposed to an accelerated carbonation curing regime with 20% concentration of $CO_2$, 60% relative humidity, and a temperature of $20^{\circ}C$ until tested at 3d, 7d, 14d and 28d. After 28d of $CO_2$ accelerated curing, in the paste containing $Mg(OH)_2$, magnesian calcite was detected by SEM-EDX. Meanwhile, the paste containing $Mg(OH)_2$ exhibit the better pore distribution than ordinary Portland cement paste and the compressive strength of the cement paste containing $Mg(OH)_2$ were more than 50Mpa.

• 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 Institute of Building Construction
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• v.16 no.3
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• pp.219-227
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• 2016

Chloride ions ingress continuously in reinforced concrete through pores of it by $Cl^-$. Finally, it causes a localized corrosion of the rebar and then it generates cracks on concrete structures. Recently, new materials removing harmful anions have been developed. Layered double hydroxides(LDHs) has an excellent ability to remove harmful anions because various anions can be adsorbed in the interlayer space between divalent and trivalent cations. Thus, LDHs has been applied in various fields. Especially, LDHs is expected to be effective adsorbent binding chloride ions. In this study, $Ca/Al-NO_3$ and $Mg/Al-NO_3$ LDHs were prepared by using a co-precipitation method. $Ca/Al-NO_3$ and $Mg/Al-NO_3$ LDHs were compared and analyzed by using XRD, SEM analysis. Many nano size hexagonal crystals were observed by SEM. Experiments for binding chloride ions of LDHs were conducted by using potentiometric method. The experimental data were measured every 15 minutes. It was observed that the chloride ion content is reduced by increasing of LDHs mass fraction and the reaction rate of $Mg/Al-NO_3$ is faster than $Ca/Al-NO_3$. In future studies, binding chloride capacity in cement materials will be evaluated based on results of this study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.469-483
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• 2018

Steel bars have been widely used as the primary reinforcement for Precast Segmental Concrete Lining for TBM Tunnels. Previously, studies have been carried out to gauge the potential for steel fiber reinforcement to replace the use of steel bar reinforcements in the segmental lining to reduce the amount of the steel bar reinforcement. Steel fiber reinforcements have been investigated and widely applied to SFRC TBM linings to improve the constructability of SFRC TBM linings worldwide. However, the steel fiber reinforcement often caused punctures to the water membranes inside tunnel lining and had long-term durability deterioration issues caused by steel corrosion, as well as cosmetic problems. Therefore, this paper sought to gauge the potential of synthetic fiber reinforcements, which have proven to be very attractive substitutes for steel fiber reinforcements. This study analyzed the performance of both steel and synthetic fiber reinforcements in segmental linings and evaluated the applicability of the fiber reinforcements to the TBM Precast Concrete Segmental Linings of TBM tunnels. As a conclusion, this study demonstrates that the potential use of steel and synthetic fibers in various combination, can substitute the rebar reinforcement in the concrete mix for segmental concrete linings.