https://doi.org/10.4334/JKCI.2025.37.2.125

편수정(Su-Jeong Pyeon) ; 김규용(Gyu-Yong Kim) ; 최병철(Byung-Cheol Choi) ; 이상수(Sang-Soo Lee) ; 남정수(Jeong-Soo Nam)

This study evaluated the compressive strength characteristics of lightweight aggregate mortar by replacing fine aggregates with waste glass beads (WGBs). The evaluation examined the compressive strength, plastic hardness, pH, and SEMresults of mortars with varying WGB replacement ratios. While the compressive strength of WGB-replaced mortar was lower than that of plain mortar, the addition of WGBs significantly increased the long-term compressive strength ratio. As the WGBreplacement ratio increased, the pH reduction over time was less pronounced compared to plain mortar. SEM analysis confirmed thatthe microstructure was enhanced due to ongoing hydration reactions at later ages. However, water absorption by the WGBs increasedthe porosity of the cement paste and reduced the density of the interfacial transition zone (ITZ), leading to a decline in plastichardness regardless of the WGB replacement ratio. Although WGBs did not enhance compressive strength at 28 days, it is expectedthat continuous hydration, facilitated by internal curing effects, will positively influence long-term compressive strengthdevelopment beyond 90 days.

https://doi.org/10.4334/JKCI.2025.37.2.133

정현규(Hyun-Kyu Jeong) ; 이정배(Jeong-Bae Lee)

This paper presents an experimental study focused on developing fire-resistant mortar to prevent the degradation of concrete structures exposed to fire, and evaluating its effectiveness in maintaining concrete performance. The study investigates the deterioration of the physical properties and durability of concrete when subjected to high temperatures. Tests were conducted by varying the exposure temperature and duration, measuring residual compressive strength, recording temperature history, andassessing durability. To confirm fire resistance, temperature changes were monitored after simulating a fire scenario, applying theRABT guidelines on the fitting and operation of road tunnels, as regulated by the German Federal Ministry of Transport and DigitalInfrastructure. The results revealed that higher exposure temperatures and longer exposure durations led to more significantdegradation of concrete performance, but that the application of fire-resistant mortar effectively blocked heat transfer into theconcrete, thereby preventing performance degradation. It was found that a fire-resistant mortar thickness of 20?30 mm or more issufficient to ensure the required fire resistance performance.

https://doi.org/10.4334/JKCI.2025.37.2.143

김형근(Hyung-Geun Kim) ; 양근혁(Keun-Hyeok Yang) ; 김용현(Yong-Hyun Kim) ; 김재포(Jae-Po Kim)

This study examined the composite behavior at the interface between precast peripheral concrete and cast-in-placeconcrete in a hollow section, as part of the development of a hollow column technique. The main test parameters included the amountof supplementary ties passing through a hollow core, the presence of burring hole protrusions designed to accommodate the hollowsection, and the configuration of the supplementary ties. Shear transfer and slip were measured using push-out test specimens thatsimulated the developed hollow column sections, incorporating both precast peripheral concrete and cast-in-place concrete. Theshear transfer due to the shear friction mechanism of the supplementary ties and the dowel action of the burring hole protrusions at theinterfacial failure plane was considered for the composite response at the interface. The test results indicated that the burring holeprotrusions played a significant role in controlling slip between the two concrete blocks along the interface. As a result, thesupplementary ties and burring hole protrusions were found to be effective in achieving a fully composite response at the interface,enhancing the integrity of the hollow column technique.

https://doi.org/10.4334/JKCI.2025.37.2.151

권성준(Seung-Jun Kwon) ; 고경택(Kyung-Taek Koh) ; 김경철(Kyong Chul Kim) ; 임광모(Kwang-Mo Lim) ; 윤용식(Yong-Sik Yoon)

The rapid chloride penetration test (RCPT) is widely used for evaluating and interpreting the chloride durability ofconcrete structures due to its relatively simple procedure and short testing time. However, its inherent characteristic of electricallyaccelerating chloride ion movement often leads to overly conservative durability assessments. In this study, the relationship betweenlong-term outdoor marine exposure tests performed under multi-level exposure conditions and rapid chloride permeability testsconducted indoors was analyzed. Data from previous studies were utilized, involving both long-term marine exposure tests and RCPTassessments on concrete mixtures incorporating ordinary Portland cement (OPC), ground granulated blast furnace slag (GGBFS), andfly ash (FA) with varying water-to-binder ratios. The experimental results were analyzed to assess the effects of concrete age andwater-to-binder ratio on chloride durability. Furthermore, a multiple linear regression analysis was performed, using passed charge andexposure duration (aged days) as input variables and the apparent chloride diffusion coefficient as the output variable, to evaluate therelationship between the two test methods. The analysis revealed determination coefficients (R²) ranging from 0.75 to 0.94 across allconditions, indicating a strong correlation between the two methods. However, relatively lower determination coefficients wereobserved for certain mixtures, and these were attributed to structural limitations of the linear regression model.

https://doi.org/10.4334/JKCI.2025.37.2.165

문주현(Ju-Hyun Mun)

The objective of this study is to examine the effect of void formers on the flexural behavior of semi-precast concreteone-way slabs using lightweight aggregate concrete with micro-steel fiber (SPCS_FLWC). The main parameters are the type oflongitudinal reinforcement and the presence or absence of void formers. Four simply supported SPCS_FLWC specimens wereprepared and tested under a top two-point load. Test results showed that although the SPCS_FLWC specimens were made oflightweight aggregate concrete, which has lower flexural crack resistance performance than normal-weight concrete and incorporatingvoid formers, their first cracking moment and maximum moment of the SPCS_FLWC specimens were higher than the valuespredicted by KDS 14 20. However, specimens with void formers exhibited brittle post-peak behavior in the load?deflectionrelationship, due to horizontal cracks at the interface between the upper SPC slab and the lower topping concrete. This resulted in alower displacement ductility ratio. Furthermore, the displacement ductility ratio was lower than the value predicted by the nonlinearanalysis procedures proposed by Yang et al.

https://doi.org/10.4334/JKCI.2025.37.2.177

정자혜(Jahe Jung) ; 이종석(Jong-Suk Lee)

In this study, coastal airborne chloride levels were investigated along the entire coastline of South Korea. Monthlymeasurements were taken for a total of three years, from July 2021 to June 2024, at 64 coastal locations, including Jeju Island. Weanalyzed the regional variations in coastal airborne chloride and their reduction patterns with increasing distance from the shoreline. The results showed that at a distance of 100 meters from the shoreline, the coastal airborne chloride levels for the eastern coast,western coast, southern coast, and different regions of Jeju Island (east, west, south, and north area) were recorded as follows: 4.0,3.8, 1.6, 32.9, 13.0, 4.0 and 10.6 mdd, respectively. The highest levels were observed on Jeju’s eastern coast, and the lowest wererecorded on the southern coast. Notably, chloride levels in Gochang (western coast) and Geoje (southern coast) were more than threetimes and over 3.4 times higher, respectively, than the average for their respective coastline areas. Reduction equations for coastalairborne chlorides were derived for each region, confirming that chloride levels decrease with increasing distance from the shore. Therate of reduction was most significant on Jeju’s western coast and least pronounced along the southern coast.

https://doi.org/10.4334/JKCI.2025.37.2.187

구현철(Hyun-Chul Koo) ; 이윤우(Yun-Wu Lee) ; 이재훈(Jae-Hun Lee) ; 조형규(Hyeong-Kyu Cho)

The demand for electromagnetic shielding has recently increased in specific domains, such as in military facilities,power transmission, and hospitals. To address this need, while promoting by-product recycling and cost efficiency, this studydeveloped a solid-state carbon capsule to enhance dispersibility in concrete. The capsule was produced using carbon-basedby-products, such as carbon nanotubes (CNTs) and cathode materials generated in the lithium secondary battery industry. Theheating performance of mortar blended with solid-state carbon capsules was evaluated, revealing that when 23 % of the capsuleswere incorporated, the surface temperature rose by more than 60 °C within 20 minutes and by 30 °C within about 16 minutes frominitial temperature. This indicated the formation of an effective electrical network. Through the electromagnetic shieldingperformance tests of concrete blended with solid-state carbon capsules, it was found that the electromagnetic shielding performanceimproved as the proportion of solid-state carbon capsules increased. Notably, when 30 % of the capsules were incorporated, theshielding effectiveness exceeded 60 dB.

https://doi.org/10.4334/JKCI.2025.37.2.195

신형엽(Hyeongyeop Shin) ; 이득행(Deuckhang Lee) ; 강현구(Thomas H.-K. Kang)

The current KDS 14 20 22 prestressed concrete (PSC) one-way shear design provision provides two approaches forconcrete shear strength (?): approximate and detailed methods. Since its first introduction in the 1983 Concrete Standard Specificationsin Korea, the safety and practicality have been thoroughly validated. However, issues remain, such as relatively complex calculation,inconsistent definitions for effective depths (? and ??), and application range for the approximate method that lacks sufficientmechanical basis. This study proposes modifications regarding these issues to reduce complexity and inconsistency while retainingthe basic philosophy of the current method. The proposed revision includes: (1) simplifying the flexure-shear strength (??) equationby removing the self-weight dead load terms and integrating them with the external load terms; (2) redefining the application rangefor the approximate method based on the average compressive stress by prestressing (???, or ????); and (3) introducing a new effectivedepth (??) specifically for the approximate method. The proposed modification is expected to maintain accuracy and conservatismcomparable to the current method while improving practical applicability by reducing calculation complexity.

https://doi.org/10.4334/JKCI.2025.37.2.207

서동주(Dong-Ju Seo) ; 전형민(Hyung-Min Jun) ; 박종건(Jong-Gun Park) ; 최범균(Beom-Gyun Choi) ; 허광희(Gwang-Hee Heo)

Conductive sidewalk blocks are created by adding a conductive agent to conventional sidewalk blocks and applyingcurrent through electrodes embedded within the blocks. The heat generated by this process can melt snow and ice in areas prone tofreezing, such as sidewalks and pavements. This study investigated the effects of conductive materials, specifically multi-walledcarbon nanotubes (MWCNTs) and carbon fibers (CFs), on the flow performance, self-heating capability, and electrical properties ofconductive sidewalk blocks (Type I). Experimental results showed that as the mixing concentration of MWCNTs and the amount ofCF increased, the self-heating performance improved and significantly reduced electrical resistivity. Additionally, while the plaincement mixture and the cement mixtures mixed with MWCNT satisfied the target flow value of 180 mm, cement mixtures mixedwith only CF exhibited a significant reduction in flow performance due to clumping. High-resolution field-emission scanningelectron microscopy (HR FE-SEM) analysis confirmed that MWCNTs were relatively evenly distributed within the cement matrixalongside CF.

https://doi.org/10.4334/JKCI.2025.37.2.219

김예은(Yeeun Kim) ; 김수빈(Subin Kim) ; 이기학(Kihak Lee) ; 신지욱(Jiuk Shin)

This study proposes a machine learning model with a combining method capable of accurately evaluating the blastresistance performance of reinforced concrete (RC) columns using a small dataset of 200 samples. To achieve this, a blastperformance evaluation response database was established based on finite element analysis models that consider various columndetails and blast scale values. Each individual learning model applied seven classification algorithms, and the model demonstratingthe highest evaluation metrics was developed and combined. The proposed machine learning model achieved a 65.5 % reduction indata usage compared to an existing model based on 700 samples while improving performance by an average of 14.3 %. These resultsdemonstrate that the proposed method enables highly accurate and rapid evaluations even in data-limited environments.

https://doi.org/10.4334/JKCI.2025.37.2.229

김효정(Hyo-Jung Kim) ; 서지석(Ji-Seok Seo) ; 이방연(Bang Yeon Lee) ; 김윤용(Yun-Yong Kim)

In this study, the 3D printing quality of fiber-reinforced mortar incorporating a recycled cactus powder admixture wasevaluated. Rheological properties, visual characteristics (printing continuity and surface pore distribution), and 3D printing accuracy(dimensional error rate and layer thickness accuracy) were experimentally investigated. Experimental variables included fibervolume fraction and the amounts of superplasticizer (SP), methyl cellulose, and recycled cactus powder admixture (CS). The CS usedin this study was obtained by crushing discarded cactus stems into a dry powder. Results indicated that mortar fluidity increased asthe amount of CS increased. Furthermore, adjusting the amounts of CS and SP allows for control over fluidity changes associatedwith varying fiber volume fractions, and enables improvement of the printed product’s surface quality.

https://doi.org/10.4334/JKCI.2025.37.2.237

문도영(Do Young Moon) ; 이강진(Kang Jin Lee)

In this study, the effect of forced alignment of steel fibers using an electromagnetic field on the distributioncoefficient, orientation coefficient, and fracture energy was analyzed through a three-point bending test. Flexural specimens withsteel fibers aligned under an electromagnetic field, varying in volume fraction and aspect ratio, were fabricated and tested alongsidecontrol specimens cast without electromagnetic exposure. Experimental results indicated that while the electromagnetic field hadminimal influence on the distribution of steel fibers, it significantly affected their orientation. It was observed that steel fibers alignedperpendicular to the fracture plane contributed to an increase in fracture energy. Based on the analysis of the effective steel fiberreinforcement ratio and fracture energy, a trend analysis was conducted, and an equation was proposed to evaluate the fracture energyof steel fiber-reinforced flexural specimens with aligned fibers subjected to an electromagnetic field.

https://doi.org/10.4334/JKCI.2025.37.2.247

최홍순(Hong-Sun Choi) ; 허무원(Moo-won Heo) ; 이현호(Hyun-Ho Lee) ; 류정식(Jeong-Sik Ryu)

This work proposes a seismic retrofit method using concrete-filled steel tube(CFT). To evaluate the effectiveness ofthis approach, a material test was conducted on a post-installed anchor that directly connects the existing frame to the CFT, alongwith a cyclic loading test on a reinforced column. In addition, in order to verify the improvements in seismic performance, two testspecimens were fabricated: a two-story, one-span reinforced concrete frame representing an existing structure and a CFT-reinforcedframe. Both specimens underwent repeated loading tests to measure seismic performance enhancements. The tensile and shearstrength test results of the anchor were found to exceed the average design strength specified by the manufacturer. Experimentalresults from the CFT-reinforced column specimens showed an increase in yield load ranging from about 105% to 125% and anincrease in maximum load from 110% to 140% compared to the reference specimen. As a result of the two-story frame experiment,the CFT-reinforced specimen exhibited a maximum strength of about 2.3?2.6 times greater than that of the non-retrofitted specimen. In addition, the energy dissipation ratio of the non-retrofitted specimen to the CFT-reinforced specimen was approximately 2.22,indicating that the double-frame reinforcement significantly enhanced energy dissipation.