• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.79-88
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• 2023

In this study, a development of the rust formation arising from steel corrosion was modelled to quantify the structural impact in steel reinforced concrete. The interfacial gap, cover depth and diameter of steel rebar were taken for variables in modelling. It was found that the interfacial gap was the most influencing on the structural limit at steel corrosion, followed by steel diameter and cover depth. At 75 mm of cover depth with 20 mm of the steel diameter, the rust amount to reach cracking accounted for 16.95-27.69 ㎛ to 1-10 ㎛ of the interfacial gap. It was found that there was no risk of cracking and structural limit until the rust was formed within the interfacial gap. With a further formation of rust, the concrete section was successively behaved to yielding, cracking and failure. Additionally, the interfacial gap was the most dominant parameter for the rust amount to reach the cracking of concrete at the interfacial zone, whilst the cover depth had a marginal effect on cracking but had a crucial influence on the rust to failure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4C
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• pp.283-290
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• 2006

Concrete has advantages in fire situations as it is non-combustible and has low thermal conductivity. However, concrete that is not designed against fire can experience significant explosive spalling from the build-up of pore pressures and internal tensile stresses when heated. In this study, the performance of wet-mixed high strength sprayed polymer mortar for fire resistance of tunnel system was evaluated by experimentally and numerically. The fire test was performed in fire resistance(electric) furnace according to RABT(Richtlinien fur die Ausstatung und den Betrieb von $Stra{\beta}entunneln$) time heating temperature curve, so as to evaluate the temperature distribution with cover thickness of wet-mixed high strength sprayed polymer mortar for fire resistance of tunnel system. Based on experimental results and numerical analysis, the proper cover thickness of wet-mixed high strength sprayed polymer mortar determined the more than 4cm.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.65-72
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• 2016

Service life evaluation for RC Structures exposed to chloride attack is very important, however the previous two methods(deterministic and probabilistic method) show a big difference. The paper presents a service life simulation using deterministic and probabilistic method with time-dependent diffusion coefficient. Three different cases are considered for diffusion coefficient, concrete cover depth, and surface chloride content respectively, and then the PDF(probability of durability failure) and the related service life are obtained. Through adopting time-dependent diffusion, the discrepancy between the two methods can be reduced, which yields reasonable service life. When diffusion coefficient increases from $2.5{\times}10^{-12}m^2/sec$ to $7.5{\times}10^{-12}m^2/sec$, the service life decreases to 25.5~35.6% level, and cover depth does from 75 mm to 125 mm, it increases to 267~311% level as well. In the case of surface chloride content from $5.0kg/m^3$ to $15.0kg/m^3$, it changes to 40.9~54.5%. The effect of cover depth is higher than the others by 8~10 times and also implies it is a key parameter to service life extension.

• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.475-482
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• 2014

This paper presents the experimental results concentrically reinforced concrete tension members and compares cracking behavior of amorphous steel fiber and normal steel fiber reinforced concrete members. Two kind of steel fibers were included as a major experimental parameter together with the six cover thickness to bar diameter ratio ($c/d_b$). The presence of amorphous steel fibers effectively controlled the splitting cracks initation and propagation. In the amorphous steel fiber reinforced specimens, no splitting cracks were observed that becomes higher with cover thickness to bar diameter ratio is 2.0. Crack spacing of the each specimens reinforced with amorphous steel fibers and normal steel fibers becomes larger with the increase in cover thickness, and also measured maximum and average crack spacing are significantly smaller than current design code provision. Based on the measured crack spacings, a relationships for predicting the crack spacing is proposed using the measured average crack spacing in amorphous steel fiber reinforced concrete tension members.

• Journal of the Korea Concrete Institute
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• v.26 no.5
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• pp.581-589
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• 2014

This paper presents the tension stiffening behavior from experimental results of each 6 amorphous steel fibers and normal steel fibers reinforced direct tensile specimens with the main variables such as cover thickness to bar diameter ratio. A tension stiffening effect for steel fiber reinforced RC tension members improve on the increase in cover thickness, and also amorphous steel fiber is usually superior to normal steel fiber. The reinforcement of steel fibers controlled the splitting cracks and led to significant increase in the tension stiffening effect. In particular, if cover thickness is more than twice the bar diameter, the amorphous steel fiber reinforced specimen is controlled the splitting crack and increased the tension stiffening effect. And, the tension stiffening effect of amorphous steel fiber reinforced concrete tension members is different to current structural design code provision.

• Journal of Navigation and Port Research
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• v.39 no.4
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• pp.335-344
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• 2015

This study aims to assess the effectiveness of zeolite, montmorillonite, and steel slag as capping materials to block the release of heavy metals from marine sediment depending on their depths. The results showed that all capping materials used this study were not effective in interrupting release of As. Zeolite had negative effect on the block of Cr release but it was significantly reduced to 5 cm by montmorillonite capping. In contrast to As and Cr, Cd, Ni, and Pb were not released even from uncapped sediments. Cu and Zn were the heavy metals those were most significantly influenced by the capping conditions. Cu release from marine sediments were effectively blocked by more than 1 cm depth of montmorillonite and more than 3 cm depth of zeolite. All capping materials were found to be effective in interrupting release of Zn from marine sediments. It was concluded that the zeolite, montmorillonite, and steel slag could be used as a potential capping material for interrupting the release of Cr, Cu, and Zn from the contaminated marine sediments.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.131-141
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• 2010

The objective of this study was to propose a development length equation for GFRP bars. A total of 104 modified pullout tests were completed while the test variables were embedment length (15, 30, $45d_b$), net cover thickness ($0.5{\sim}2.0d_b$), top-cast bar effect, different GFRP bar types (K2KR, K3KR and AsUS), and bar diameters (10, 13, 16 mm). Average bond stresses were determined based on modified pullout test results. Two variable linear regression analysis was performed of the average bond stresses. Utilizing 5% fractile concept, a conservative development length design equation was derived. The design equation derived in this study was compared to the ACI 440 committee equation. The cross-comparison revealed that the current equation resulted in shorter development lengths than those determined by the ACI 440 equation when the net cover thickness was large (greater than $1.0d_b$). On the other hand, when the net cover thickness was small (equal to or less than $1.0d_b$), the development lengths required by the current equation were larger than those by the ACI equation. The bond stresses were significantly influenced by the cover thicknesses. The current equation results in development lengths that are more economical when the cover thickness is large, and more conservative lengths when the cover thickness is small than the ACI 440 committee equation.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.229-235
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• 2010

In this study, fire resistance performance of high strength concrete specimen with fireproof gypsum board was investigated for possible use in upgrading fire-resistant performance of the existing building and repair of fire damaged structures. Fire test of eight identical high strength concrete columns were carried out for 180 minutes in accordance with ISO-834. The temperature distributions in longitudinal reinforcement and concrete temperature at various depths were recorded. The fireproof performance of gypsum board and explosive spalling of concrete were observed. The specimens with 15 mm thick twoply fireproof gypsum board spalled after gypsum board crumbled regardless of fastening methods. However, when the thickness of fireproof gypsum board was more than 30 mm, it was possible to prevent the explosive spalling and control the rebar temperature. Although the effect of cover thickness could not be compared because the explosive spalling occurred, there seemed to be no difference in insulation efficiency.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.124-132
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• 2022

The corrosion potential in concrete varies greatly with exposure and concrete mix conditions. In this study, RC (Reinforcement Concrete) samples were prepared considering cover depth, chloride concentration, and W/C(water to cement) ratio as variables, and HCP(Half Cell Potential) was measured, which evaluated comparative potential between embedded steel and concrete surface. In addition, OCP(Open Circuit Potential) was measured using buried steel and CE(Counter Electrode). Agar and NaOH solution were used as ion exchange materials and Hg/HgO was used for RE(Reference Electrode), which was more sensitive to temperature than HCP. Among the influencing factors, the exposure period and chloride concentration had a relatively greater effect than cover depth and w/c ratio. Additionally, the entire measured HCP and OCP showed a clearly linear relationship with increasing cover depth and w/c ratio. Through multiple regression analysis, the relationship between HCP and OCP was quantified, and an improved correlation was obtained with temperature effect.

• Fire Science and Engineering
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• v.29 no.4
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• pp.1-6
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• 2015

It is necessary to obtain a fire resistance certification in order to use SFRM in Korea. The fire resistance tests for certifications are performed separately for beams and columns and the certifications are different. We could assume that the same SFRM has different thicknesses for beams and columns because the conditions of the fire resistance tests for them differ in the section factors etc. But most of the SFRMs in Korea have the same thicknesses for beams and columns. So the question arises as to there were the differences between the fire test results for beams and columns reside. The purpose of this study is to consider the separate evaluation of the fire resistance of members through a comparative analysis of the temperature data obtained from fire certification tests.