https://doi.org/10.4334/JKCI.2025.37.4.407

박완신(Wan-Shin Park) ; 장영일(Young-Il Jang) ; 김선우(Sun-Woo Kim) ; 윤현도(Hyun-Do Yun)

To optimize the panel shear capacity of hybrid coupled wall systems, a novel set of replaceable connection details between the steel link beam and concrete shear walls is proposed. The objective of this study was to investigate the panel shear capacity of steel link beam-to-wall connection in hybrid coupled shear wall systems. The key parameters considered in this study included the presence or absence of fibers, face bearing plates, and horizontal ties in the panel zone. The study results showed that theshear strength of all the specimens in the pseudo strain hardening cementitious composite (PSH2C) group was greater than or equal to that of the hybrid coupled wall system (HCWS) group. However, the findings also reveal that the contribution of connection strength?depending on the presence of PVC fibers and specific connection details in the PSH2C group?requires further evaluation and potential revision to accurately assess the panel shear strength of steel link beam-to-wall connections.

https://doi.org/10.4334/JKCI.2025.37.4.417

김원창(Won-Chang Kim) ; 이태규(Tae-Gyu Lee)

In this study, a statistical analysis and a machine learning-based model were developed and evaluated to predict concrete quality using data from a previous study on concrete strength prediction via ultrasonic pulse velocity (UPV) after exposure to high temperatures. A total of 22 studies on normal concrete were collected, and the data were categorized into four levels (W/C50, W/C40, W/C30, and W/C20) based on the W/C ratio. The results showed that both the mean and the standard deviation of compressive strength increased as the W/C ratio decreased. However, UPV and residual compressive strength did not exhibit significant variations across the categories. ANOVA tests performed on the four W/C ratio groups revealed statistically significant differences in compressive strength, except between W/C50 and W/C40. No significant differences were observed for UPV and residual compressive strength. In the simple linear regression analysis, although the p-value was below the significance threshold of 0.05, the R2 was very low, at about 0.47. Furthermore, in the multiple linear regression analysis, the residuals did not satisfy the assumption of homoscedasticity. When building and evaluating models using machine learning?based regression algorithms, both Random forest and XGBoost performed very well, with R2 values above 0.92 and RMSE values below 0.1.

https://doi.org/10.4334/JKCI.2025.37.4.427

방자호(Ja-Ho Bang) ; 최지완(Ji-Woan Choi) ; 권성준(Seung-Jun Kwon)

Service life is evaluated differently depending on the quantification of environmental deterioration, resistance mechanisms, and design methods. In this study, the service life of precast (PC) box structures in nuclear power plant structures constructed in the UAE was assessed with respect to sulfate attack. Concrete samples were prepared based on the obtained mixing materials, and the mean and coefficient of variation (COV) of the sulfate ion diffusion were determined through natural diffusion tests. Service life was evaluated through deterministic and probabilistic methods based on Monte Carlo simulation (MCS) and the linear degradation depth method, respectively, and the influence of various design parameters on the predicted service life was analyzed and discussed. Owing to design variables such as the environmental load factor, durability acceleration factor, and marginal erosion depth for safety, the deterministic design method was found to be slightly conservatively; however, no significant differences were observed. When the external sulfate concentration exceeded 200 ppm and the COV of aluminum oxide content was high, the results showed considerable variation, highlighting the importance of sufficient cover depth and stringent material quality control. Furthermore, it is necessary to quantify the variability of design parameters for the target structure (such as cover depth, external sulfate concentration, and diffusion coefficient) to enable a more accurate and reliable prediction of service life.

https://doi.org/10.4334/JKCI.2025.37.4.435

응웬 후 바오 안(Ngan H. B. Nguyen) ; 이성진(Sung Jin Lee) ; 김제경(Je-Kyoung Kim) ; 이정재(Jurng-Jae Yee) ; 기성훈(Seong-Hoon Kee)

This study developed a surface-mounted miniature electrochemical impedance spectroscopy (EIS) sensor to evaluate the corrosion environment of reinforcing steel in concrete and validated its performance through comparison with existing commercial sensors. The developed sensor features a compact design that integrates both the reference electrode (RE) and the counter electrode(CE) into a single structure. It demonstrated performance comparable to that of commercial sensors under various saline conditions. Specifically, the standard potential of the developed sensor was measured to be approximately +292 mV relative to the silver/silver chloride (Ag/AgCl) electrode. It was confirmed that a correction of about +24 mV is required for assessing corrosion risk based on ASTM C876 standards. The AC impedance analysis revealed that the developed sensor effectively monitors changes in the electrical properties of concrete surfaces. By analyzing impedance signals, the solution resistance (Rs) was measured to assess the drying state of the concrete, and the analysis of capacitance (Cdl,0 and Cdl,1) values, as defined by the electrochemical equivalent circuit, provided information on saline concentrations. These findings support the utility of the developed sensor in quantitatively identifying changes in the electrochemical properties and environmental conditions of reinforced concrete structures. The surface- mounted EIS sensor proposed in this study demonstrates significant potential as a practical and non-destructive tool for corrosion monitoring in field applications.

https://doi.org/10.4334/JKCI.2025.37.4.445

서수연(Soo-Yeon Seo) ; 트란 하이 반(Hi Van Tran) ; 엠 후자이파 요누스 투르(M. Huzaifa Younus Toor)

The purpose of this study was to investigate the bond failure behavior of near-surface-mounted (NSM) carbon fiber?reinforced polymer (CFRP) reinforcements with rectangular cross-sections, focusing on the effects of reinforcement size and bond length. To achieve this, nine concrete block specimens were prepared and strengthened with NSM CFRP reinforcements, then subjected to pull-out tests. The experimental variables included three different cross-sections of CFRP reinforcements, each tested with three different bond lengths. In the experiment, all specimens exhibited bond failure at the interface between the CFRP reinforcement and the concrete. Among the tested configurations, the thin plate-type reinforcements demonstrated the highest bond efficiency as bond length increased. Furthermore, the debonding strength, at which slippage at the bond interface begins to occur, was found to be proportional to the bond area, which is calculated as the product of the interface perimeter and the bond length. Based on regression analysis of this relationship, a suitable formula was proposed to appropriately predict the bond strength.

https://doi.org/10.4334/JKCI.2025.37.4.453

전상민(Sangmin Jeon) ; 김형기(Hyeong-Ki Kim)

A comprehensive understanding of the effects of carbonation on the chemical and physical properties of concrete remains limited. This study investigates the impact of carbonation on concrete compressive strength through both experimental analysis and a review of existing literature. Representative mortar mixtures were subjected to two carbonation conditions: long-term carbonation (continuous exposure from the first day of curing) and short-term carbonation curing (applied after the first day of sealed curing, followed by 24 or 72 hours of intensive carbonation and subsequent underwater curing). Compressive strength was then measured, and the results were analyzed in conjunction with previous studies to identify trends. Based on these findings, the mechanism underlying the effects of carbonation on the compressive strength of concrete are discussed.

https://doi.org/10.4334/JKCI.2025.37.4.463

오영훈(Young-Hun Oh) ; 신익수(Ik-Su Shin) ; 강승일(Sung-Il Kang) ; 문정호(Jeong-Ho Moon)

This study presents an experimental investigation into the shear strength of hollow core slabs (HCS) produced by extrusion forming. A total of 21 slab specimens were tested to evaluate both web-shear and flexural-shear strengths. The specimens included PC-HCS with heights of 200 mm, 320 mm, 350 mm, 400 mm, and 500 mm. For each height, specimens were classified into four test methods (TM-1, TM-3, TM-4, TM-5), based on variables such as topping concrete, presence of shear reinforcement, and failure modes. The experimental results were analyzed using strength ratios relative to the design strengths in the KDS. The findings revealed that web-shear specimens without shear reinforcement (TM-1, TM-3) exhibited strength ratios greater than 1.0, while specimens with shear reinforcement (TM-4) showed strength ratios below 1.0. Flexural-shear specimens (TM-5) displayed a high strength ratio distribution and exhibited failure modes approaching flexural failure. Based on these findings, it was concluded that the contribution of shear reinforcement to overall shear strength should be evaluated lower than the design standards. Additionally, the flexural-shear strength evaluation method yielded conservative estimates. Since web-shear failure will typically be evaluated near the support points, it is important to fabricate the slabs in a way that prevents excessive tendon slip.

https://doi.org/10.4334/JKCI.2025.37.4.473

이기연(Ki-Yeon Lee) ; 양근혁(Keun-Hyeok Yang)

This study presents a preliminary investigation into the development of a crack-healing mortar for precast concrete joints, designed to enhance crack healing, control, and toughness. For the purpose of promoting crack-healing, 4 % of the mortar volume was replaced with an inorganic material and bacteria-based healing agent proposed by Yoon et al. (2022) and Lee et al. (2024). To improve tensile resistance and toughness, micro steel fiber content was varied from 0.25 % to 0.5 %, and aramid fiber content from 0.5 % to 0.75 % by volume. The compressive toughness index of the fiber-reinforced mortar was evaluated based on the stress?strain relationship in accordance with ASTM C1018. Flexural toughness was evaluated using both the flexural toughness index (per ASTM C1018) and the residual flexural strength values (as defined in fib Model Code 2010). Experimental results showed a crack-healing rate of 93 % at 28 days. Mortars reinforced with a hybrid combination of micro steel and aramid fibers exhibited the most ductile descending slopes in both the flexural load?displacement and flexural stress?CMOD (crack mouth opening displacement) relationship. Notably, compared to specimens reinforced with 0.5 % micro steel fibers alone, those incorporating a hybrid of 0.25 % micro steel fibers and 0.25 % aramid fibers exhibited higher residual flexural strength when crack widths exceeded 2.5 mm. These findings indicate that the proposed mortar design approach demonstrates good potential for application in precast concrete joints, offering improved crack-healing capacity and mechanical toughness.

https://doi.org/10.4334/JKCI.2025.37.4.481

이현호(Hyun-Ho Lee) ; 문철(Cheol-Mun)

In this study, the mixing characteristics and 28-day compressive strength of ready-mixed concrete delivered to a construction site were evaluated before and after the implementation of a quality inspection standard for unit water content. Our dataset comprised 61 mix designs and 594 compressive strength test results. The compressive strength of concrete specimens, cast during site acceptance testing of the ready-mixed concrete, was assessed. The results indicated a reliable correlation between unit water content and compressive strength after the application of the unit water content quality inspection standard.

https://doi.org/10.4334/JKCI.2025.37.4.489

이영욱(Young-Wook Lee) ; 이찬희(Chanhui Lee) ; 고수경(Sookyung Ko)

In this study, the effect of foundation modeling on the seismic performance after seismic retrofitting was investigated for a building with isolated shallow foundations and a large ratio of short sides to long sides such as found in a typical elementary school. To examine the effectiveness of seismic retrofitting, a three-story building located in seismic zone I and on soil profile type S2 was selected. The retrofitting design incorporated four variations of horizontal stiffness achieved through the use of steel bracing. For the nonlinear static analysis, two methods of modeling the foundation were used: the commonly used fixed-base model and a model incorporating six-degree-of-freedom (6-DOF) springs. The nonlinear static procedure was applied to each of the four re-strengthened models using both foundation modeling types to evaluate and compare the seismic performance of the RC frame and foundation. The results indicated that it is preferable to use 6-DOF springs, because using a fixed-base model will overestimate the lateral stiffness, which may lead to unsatisfactory performance of the foundation. However, the spring model can lead to brittle shear failure in the columns due to increased deformation. Therefore, care should be taken to limit the horizontal deformation in retrofitted buildings.

https://doi.org/10.4334/JKCI.2025.37.4.499

이인규(Inkyu Rhee)

A square concrete slab measuring 2,550 mm in length and 180 mm in thickness was modeled using three-dimensional solid elements, incorporating both conventional reinforcement bars and hooked-end steel fiber inclusions. To accurately represent the composite behavior of steel fiber?reinforced concrete (SFRC), explicit fiber modeling was adopted on the basis of homogenized concrete. The nonlinear behavior of the concrete was captured using a damaged plasticity model. A punching shear load was applied vertically upward at the center of the slab and increased incrementally until radial cracking led to failure in the simulation. To account for the inherent variability of punching shear behavior and to explore potential enhancements in ductility, the shear resistance performance of the SFRC slab was evaluated under varying fiber orientations and aspect ratios.

https://doi.org/10.4334/JKCI.2025.37.4.509

허무원(Moo-Won Heo)

In this work, a mechanical connection method applicable to joints between existing and new structures during horizontal extension remodeling of apartment buildings is proposed. The proposed method comprises a mechanical connection detail that utilizes post-installed expansion anchors and head studs, offering excellent structural performance and constructability compared to existing chemical anchors. To evaluate the structural behavior and performance of the proposed connection detail, a series of material- and component-level experiments was conducted. The validity of the system was verified through pull-out and shear tests on post-installed expansion anchors embedded in existing concrete members. The results showed that the characteristic strengths of all anchors met or exceeded the manufacturer’s standard values, demonstrating adequate structural safety and reliability under both tensile and shear loads. Furthermore, additional pull-out and shear tests were performed on assemblies of wedge anchors and connecting materials under varying reinforcement spacings (120 mm, 130 mm, and 150 mm). In all cases, the characteristic strengths exceeded the nominal tensile and shear strength values specified in the Design Standard for Anchors for Concrete (KDS, 2021), confirming that the proposed connection provides sufficient performance that exceeds the minimum nominal strength required by the standard.

https://doi.org/10.4334/JKCI.2025.37.4.517

정재용(Jae Yong Jeong) ; 우진석(Jin Seok Woo) ; 최원창(Won Chang Choi) ; 김선우(Sun Woo Kim) ; 박완신(Wan Shin Park) ; 윤현도(Hyun Do Yun)

Biochar has gained attention as an alternative material capable of simultaneously delivering carbon reduction effects and desirable physical properties as a construction material. Recent studies have extended its application beyond cementitious admixture to include partial replacement for both coarse and fine aggregates. This study critically reviewed 21 key publications, categorizing the use of biochar based on its substitution for coarse and fine aggregates. Incorporation rates ranged from 1 % to 40 % by weight or volume, with the resulting compressive strength varying depending on the replacement ratio and pyrolysis conditions. Biochar also demonstrated excellent carbon sequestration capacity, indicating its potential not only as a replacement material but also as a carbon-reducing construction resource. However, most studies have focused on mechanical performance and mix design properties, while research on long-term durability and constructability remains limited. In conclusion, biochar has been identified as a promising material capable of providing both structural performance and carbon storage. Nevertheless, further research is needed to establish standardization evaluation criteria and to validate its long-term performance for practical implementation.