https://doi.org/10.4334/JKCI.2026.38.2.129

김유민(Yu-Min Kim) ; 이문석(Moon-Seok Lee) ; 손동희(Dong-Hee Son) ; 배백일(Baek-Il Bae) ; 최창식(Chang-Sik Choi)

This study examined the fire resistance performance of normal-strength concrete mixed with polypropylene (PP) fibers. While previous research has focused mainly on high-strength concrete and micro fibers, this study explored how fiber shape and volume fraction can affect the residual properties after fire exposure. Test results showed that fiber inclusion contributed to the improvement of mechanical strength at room temperature, and macro fibers were generally more effective than micro fibers. However, after thermal exposure, all specimens showed reduced mechanical properties and similar deflection behavior regardless of fiber content. Compared to 94 test results reported in previous studies?primarily focused on high-strength concrete?the specimens in this study exhibited lower residual compressive strength. This difference can be attributed to the increased porosity and more severe decomposition of hydrates in normal-strength concrete after exposure to elevated temperatures, highlighting the need for refined prediction models tailored to this material.

https://doi.org/10.4334/JKCI.2026.38.2.139

박주혜(Joohye Park) ; 이준영(Junyoung Lee) ; 홍진영(Jinyoung Hong) ; 최하진(Hajin Choi)

The water-to-cement ratio (w/c), a key indicator of concrete quality, has a significant influence on both compressive strength and durability. Theoretically, the minimum w/c required for complete hydration is 0.36. In practice, however, discrepancies between the design and actual values frequently arise due to factors such as mixing mistakes, evaporation loss, and residual wash water. This highlights the need for a simple and accurate on-site method to evaluate the w/c ratio. We propose a classification model based on electrical impedance data to rapidly identify concrete mixtures that fail to meet the minimum w/c threshold (36 %) during site acceptance. Unlike conventional equivalent circuit model (ECM) approaches, our proposed method utilizes raw impedance data from early-age cement paste. After statistically confirming its classification potential, a random forest algorithm was employed to build an optimized model. The model was evaluated using cement paste datasets with various w/c ratios, achieving a classification accuracy of 92.5 % and an area under the curve (AUC) of 0.982 for the 36 % threshold, along with a macro-average F1-score of 0.917. These results demonstrate the feasibility of detecting substandard concrete through simple measurements and analysis, and suggest its potential for integration into automated quality control systems.

https://doi.org/10.4334/JKCI.2026.38.2.147

김우혁(Woo-Hyeok Kim) ; 양지수(Ji-Su Yang) ; 민근형(Geun-Hyeong Min) ; 김우석(Woo-Seok Kim)

Our goal was to predict the long-term performance of concrete bridge decks in Korea by integrating inspection records from the Facility Management System (FMS) with regional climatic data. Based on a dataset of 5,353 bridges, several preprocessing procedures were applied, including imbalance correction (SMOTE-Tomek), categorical variable transformation (One-Hot Encoding), and normalization (StandardScaler). Subsequently, four long-term prediction models were developed: Weibull, CoxPH, Lasso?Cox, and PINN-Cox. Model performance was evaluated using the Concordance Index (C-index), Integrated Brier Score (IBS), Integrated Mean Absolute Error (IMAE), and Royston?Sauerbrei’s . Among the models, the Weibull model achieved the best performance, followed by CoxPH, Lasso?Cox, and PINN-Cox. Furthermore, by converting the survival function into a cumulative distribution function (CDF) and applying monotonic regression to the average defect index (DI) with respect to service years, we propose a procedure to align probability-based predictions with actual deterioration indices. The results confirm the feasibility of estimating the long-term performance of individual bridges by applying parallel shifts to the average deterioration curve, thereby reflecting information from inspection histories.

https://doi.org/10.4334/JKCI.2026.38.2.155

정현우(Hyun-Woo Jung) ; 최승국(Seung-Guk Choe) ; 김창혁(Changhyuk Kim)

In this work, a wireless miniaturized structural deformation measurement system was developed using ultrasonic sensors to overcome the limitations of conventional wired systems. Wireless communication was achieved using Wi-Fi modules, along with compact ultrasonic sensors and Arduino boards, enabling both wireless operation and hardware miniaturization. To reduce spike noise inherent in ultrasonic distance measurements, six filtering techniques, including the Kalman filter were applied. In addition, a Multilayer Perceptron (MLP) model was employed to improve prediction performance using various combinations of these filters. Bayesian optimization and K-fold cross-validation were conducted to prevent overfitting and to determine optimal hyperparameters. As the number of filter combinations was gradually expanded and compared, the MLP model combining ultrasonic data with four filters (Kalman, Exponential Moving Average, Savitzky?Golay, and Gaussian) achieved the lowest prediction error. Additional validation using a simplified test specimen produced consistent results, confirming the effectiveness and reproducibility of the proposed approach. Through this approach, spike noise was effectively reduced, and the reliability of the measurement data was improved.

https://doi.org/10.4334/JKCI.2026.38.2.163

이용빈(Yong-Bin Lee) ; 김승희(Seung-Hee Kim) ; 최경규(Kyoung-Kyu Choi)

We experimentally investigated the mechanical and radiation shielding properties of hybrid concrete incorporating amorphous steel fibers and ultra-fine boron powders. Various mix proportions were developed to maximize radiation shielding performance while maintaining adequate workability and mechanical strength. Slump tests, compressive strength tests, and gamma-ray shielding tests were conducted to examine the relationship between mechanical and shielding properties. The results indicate that the addition of amorphous steel fibers enhances crack resistance and structural performance, while the addition of boron powders significantly improves radiation shielding performance. These findings suggest that such hybrid material can serve as a balanced radiation shielding solution with both mechanical durability and radiation attenuation capabilities.

https://doi.org/10.4334/JKCI.2026.38.2.173

노병철(Byeong-Cheol Lho) ; 서대원(Dae-WonSeo)

This paper considers the current status and emerging trends of artificial intelligence (AI) in the field of concrete structural engineering. AI applications are categorized into the following four areas and the latest research trends within each are examined: (1) structural health monitoring (SHM), (2) material and mix design, (3) structural design and analysis, and (4) construction and maintenance. In the field of structural health monitoring, significant progress has been made in automated crack and damage detection using deep-learning vision technology, internal defect diagnosis using vibration data, and the prediction of structural durability and remaining service life. In material and mix design, machine learning approaches have improved the accuracy of strength and performance predictions, while optimization techniques such as genetic algorithms have enabled optimal mix design that takes into account both cost and eco-friendliness. In structural design and analysis, AI facilitates structural optimization, reduces analysis time through metamodeling, and supports intelligent design by integrating with digital twin technologies. Finally, in construction and maintenance, AI is leading construction automation through 3D printing and robotics, and contributes to reducing life-cycle costs through predictive maintenance strategies. This paper presents core technologies and application cases for each field and proposes a blueprint for the advancement of concrete structural engineering. It also discusses technical challenges, including data acquisition, model eXplainability (XAI), and field applicability, as well as future research directions.

https://doi.org/10.4334/JKCI.2026.38.2.181

김봉준(Bong-Jun Kim) ; 염광수(Kwang-Soo Youm) ; 김기열(Ki-Yeol Kim) ; 최명성(Myoung-Sung Choi)

This study experimentally investigated the effect of cross-sectional shape on the compressive strength of concrete with identical width-to-height ratios (). Prismatic and cylindrical specimens were prepared under various curing conditions (standard and field-sealed, under cold weather and under normal weather) and ratios of 1.0, 1.5, and 2.0. The test results showed that both specimen types exhibited nearly identical strength development, with differences within 5 %. At a ratio of 2.0, cylindrical specimens showed slightly higher compressive strength than prismatic specimens. These findings indicate that prismatic specimens produced using detachable formwork during actual placement can effectively represent the in-situ quality of cast concrete and are therefore suitable for practical field quality control applications.

https://doi.org/10.4334/JKCI.2026.38.2.191

강인규(In-Gyu Kang) ; 김건우(Geon-Woo Kim) ; 이진우(Jin-Woo Lee) ; 강남규(Nam-Gyu Kang) ; 신상철(Sang-Chul Shin) ; 김진만(Jin-Man Kim)

A survey was conducted among 337 experts from the cement and concrete industries to assess industry perspectives on establishing a Korean standard for Portland Limestone Cement (PLC), aimed at reducing CO2 emissions by utilizing limestone as a supplementary cementitious material (SCM). The survey addressed key topics related to standardization, including the necessity of a PLC standard, required limestone quality parameters (CaCO3 purity, clay content, TOC, and fineness), allowable limestone replacement levels, classification criteria based on strength and limestone content, and essential physical and chemical performance requirements. The results showed that more than 70% of respondents support the establishment of a Korean PLC standard and generally hold positive views on increasing limestone usage. However, concerns regarding potential reductions in strength and durability remain significant, with CaCO3 purity, limestone content, and compressive strength identified as critical factors for ensuring quality stability. The expert insights obtained in this study are expected to serve as valuable technical and regulatory reference data for the future development of Korean PLC standards.

https://doi.org/10.4334/JKCI.2026.38.2.203

허무원(Moo-won Heo)

In this study, cyclic loading tests were performed on two-story reinforced concrete (RC) frame specimens to evaluate the seismic strengthening effects of an externally attached concrete-filled steel tube (CFT) retrofitting method, focusing on the installation location and foundation connection conditions. The experimental results showed that the externally attached CFT system was structurally linked to the existing columns, thereby sharing the entire load. All specimens exhibited a common failure pattern, with shear failure occurring at the base of the first-floor columns. After reinforcement, damage to the existing columns tended to be relatively delayed, which is believed to be a result of the externally attached CFT seismic retrofit method reducing the required deformation of the existing columns by sharing the lateral load. Furthermore, the maximum load capacities of the specimens with foundation anchorage increased by approximately 1.47 and 1.61 times, respectively, compared to the reference specimen. The presence of foundation anchorage effectively suppressed rotational deformation during the initial loading phase, thereby maintaining the structural system’s stiffness. These findings suggest that the foundation anchorage condition plays a critical role in ensuring the initial stability of the externally attached CFT seismic retrofitting method.

https://doi.org/10.4334/JKCI.2026.38.2.211

박자민(Jamin Park) ; 권승희(Seung-Hee Kwon) ; 송호민(Homin Song) ; 최정욱(Jung-Wook Choi) ; 김형기(Hyeong-Ki Kim)

This study proposes an improved framework for evaluating the compressive strength of existing concrete structures to enhance the accuracy of structural safety assessments. Current domestic and international standards often lack clear procedures or fail to account for realistic site constraints, frequently resulting in underestimations of concrete strength. To address these issues, this research presents three practical evaluation approaches: (1) a regression-based estimation method combining core testing with nondestructive testing (NDT); (2) a minimum-value-based evaluation incorporating a statistical correction factor for cases with a limited number of core specimens; and (3) a conservative estimation method for NDT-only scenarios using a reduction multiplier to account for uncertainty. Furthermore, this study provides explicit guidelines regarding the selection of test locations and the acceptance of small-diameter core specimens thereby aligning domestic practices with EN and JCI standards. Case studies on actual structures demonstrated that the proposed framework effectively mitigates the over-conservatism of existing KDS codes while providing reliable and stable characteristic strength values that reflect field conditions.

https://doi.org/10.4334/JKCI.2026.38.2.223

이대엽(Dae-Yeop Lee) ; 이성철(Seong-Cheol Lee) ; 홍근태(Geuntae Hong)

As global efforts to reduce carbon emissions intensify in response to climate change, carbon capture, utilization, and storage (CCUS) has attracted attention as a potential mitigation strategy. This study investigates concrete blocks incorporating steelmaking slag as a partial replacement for fine aggregate, focusing on their structural performance, expansion stability, and carbon dioxide (CO2) capture characteristics under a pilot-scale production process. Based on preliminary laboratory experiments, mixture conditions satisfying the performance requirements for pedestrian concrete blocks were identified, and prototype blocks were manufactured using an actual production line. The results showed that specimens incorporating basic oxygen furnace slag (BOS) and electric arc furnace oxidizing slag (EOS) exhibited superior mechanical performance and expansion stability compared to the reference mixture, while specimens with electric arc furnace reducing slag (ERS) did not fully satisfy the required criteria. Thermogravimetric?differential thermal analysis (TG-DTA) and phenolphthalein tests further confirmed enhanced CO2 capture via mineral carbonation in the BOS- and EOS-containing specimens, with the CO2 capture potential of the EOS 35 mixture estimated at approximately 59 g per block. Overall, the results demonstrated that steelmaking slag?incorporated concrete blocks can maintain adequate structural performance under pilot-scale production conditions while providing additional CO2 capture functionality through mineral carbonation.

https://doi.org/10.4334/JKCI.2026.38.2.231

손윤기(Yun-Ki Son) ; 남왕현(Wang-Hyun Nam) ; 이동원(Dong-Won Lee) ; 남문석(Moon-Seok Nam) ; 황훈희(Hun-Hee Hwang)

This study experimentally investigated the structural feasibility of using glass fiber?reinforced polymer (GFRP) bars in concrete noise-barrier foundations. Embedded and non-embedded bending tests were conducted on GFRP bars with diameters of G13 and G16, and the results were evaluated against domestic and international design standards. In addition, full-scale foundation specimens, including one steel-reinforced concrete (RC) specimen and two GFRP-reinforced specimens, were tested under monotonic lateral loading. The results showed that all GFRP bent bars satisfied the required tensile strength criteria. The GFRP-reinforced foundations achieved safety factors comparable to or greater than those of the RC foundation. Moreover, the GFRP specimens exhibited greater deformation capacity without load degradation even after entering the plastic region. These results indicate that GFRP reinforcement can be structurally applied to noise-barrier foundations when appropriate detailing is provided.

https://doi.org/10.4334/JKCI.2026.38.2.239

이진희(Jin-Hui Lee) ; 우진석(Jin-Seok Woo) ; 윤현도(Hyun-Do Yun) ; 박완신(Wan-Shin Park) ; 김선우(Sun-Woo Kim) ; 서수연(Soo-Yeon Seo)

The shear strength of precast concrete (PC) wall vertical joints depends on various factors, including horizontal reinforcement, shear keys, and joint configuration. However, current design codes do not sufficiently reflect the combined influence of these variables, resulting in significant discrepancies between predicted and observed shear capacity. To address this limitation, this study evaluated the effects of horizontal reinforcement based on the shear friction concept by comparing shear strength predictions from five major design standards?KDS 41, ACI 318, Eurocode 2, fib Model Code 2010, and CSA A23.3?with experimental results reported in available literature. The results indicated that ACI 318 provides predictions that most closely align with experimental results, while Eurocode 2 and fib Model Code 2010 tend to underestimate shear capacity. In contrast, KDS 41 and CSA A23.3 generally overestimate shear strength and do not effectively account for the influence of horizontal reinforcement. Based on the observed flexural behavior and non-yielding characteristics of horizontal bars, a refined reinforcement contribution model is proposed, offering improved reliability in predicting the shear strength of PC wall vertical joints.

https://doi.org/10.4334/JKCI.2026.38.2.251

이창근(Chang Gun Lee) ; 안기용(Ki Yong Ann)

This study presents a quantitative assessment of the durability of concrete treated with a commercial water-repellent agent. Additionally, the compatibility of the water-repellent agent was examined in terms of concrete strength, cost efficiency, durability, environmental impact, long-term feasibility, and constructability. Mortar specimens were prepared with a cement-water- sand ratio of 1.00:0.50:2.50, and a silane-based water-repellent agent was applied to the surface twice. It was found that the water-repellent agent enhanced carbonation resistance by over 60 %, meaning that the time required for carbonation to reach a certain depth increased by at least sixfold. Regarding chloride-induced corrosion, the onset of corrosion occurred between 12 and 22 weeks. In contrast, specimens treated with the water-repellent agent exhibited delayed corrosion initiation at 22 and 24 weeks, with two specimens showing no signs of corrosion even after 26 weeks of monitoring. Furthermore, the water-repellent agent refined the pore structure, leading to a densification of capillary pores in the range of 500?1,000 nm.