https://doi.org/10.4334/JKCI.2025.37.6.679

임정국(Jeong-Guk Im) ; 채경훈(Kyoung-Hun Chae) ; 박태원(Tae-Won Park) ; 허무원(Moo-Won Heo)

Post-installed anchors are widely used in concrete structures to connect structural and non-structural components due to their flexibility in installation and ease of construction. However, current design standards tend to evaluate anchor performance conservatively, as they do not adequately consider critical factors such as anchor diameter, concrete failure area, and failure angle. This study investigates the pullout strength and failure angle of torque-controlled expansion anchors (M10, M12, M16) through experimental testing under varying embedment depths. The results indicate that the measured pullout strengths generally exceeded the nominal strengths calculated by existing design formulas, suggesting that current standards may underestimate actual anchor performance. The gap between nominal and experimental strengths widened with increasing anchor diameter. Additionally, the failure angle was observed to increase as embedment depth decreased, likely due to intensified stress concentration near the surface, leading to steeper failure planes. These findings highlight the need for revised design formulas that incorporate embedment depth, anchor diameter, and failure angle to enable more accurate strength predictions.

https://doi.org/10.4334/JKCI.2025.37.6.687

최원준(Wonjun Choi) ; 이상현(Sanghyun Lee) ; 김치경(Cheekyeong Kim) ; 허석재(Seokjae Heo)

This study examines the integration of educational theories into prompt engineering to enhance the performance of large language models (LLMs) in Mechanical, Electrical, and Plumbing (MEP) schematic design tasks within the construction industry. Drawing on parallels between human cognitive processes and LLM behavior, the research hypothesizes that prompts informed by educational principles can significantly improve the accuracy and quality of AI-generated outputs. Simplified representations of complex construction diagrams are utilized to demonstrate the applicability of LLMs in MEP design scenarios. The findings indicate that embedding educational strategies into prompt engineering enhances the relevance and precision of AI-generated designs, representing an initial step toward more effective AI-assisted design workflows in construction. This paper underscores the advantages of this approach and outlines potential avenues for future research to further refine and expand its application in the construction industry.

https://doi.org/10.4334/JKCI.2025.37.6.699

이주원(Juwon Lee) ; 김민준(Min-Jun Kim) ; 홍승주(Seungju Hong) ; 홍진영(Jin-Young Hong) ; 최하진(Hajin Choi)

This study focuses on the development of a feature extraction technique based on ultrasonic testing for the purpose of evaluating the grout-filling quality of precast concrete (PC) joint sleeves. Existing grout-filling quality inspection methods, such as visual examination, are limited in their ability to assess internal filling quality after construction. To address this issue, PC joint sleeve specimens were designed and validated to reflect potential internal filling deficiencies that may occur in actual construction environments. Dry-coupled ultrasonic transducers were applied, and the excitation frequency was optimized to enhance field applicability. The collected ultrasonic signals were analyzed using a frequency feature extraction algorithm, which successfully distinguished between unfilled and filled specimens. These findings suggest that the proposed method can effectively identify differences in grout-filling quality. Future research will involve experimental validation incorporating variables such as the rebar eccentricity, partial grout filling inside the sleeves, and grout curing age.

https://doi.org/10.4334/JKCI.2025.37.6.707

박금단(Keum-Dan Park) ; 조형규(Hyeong-kyu Cho)

This work evaluated the potential use of bottom ash generated from a circulating fluidized bed (CFB) boiler as a supplementary cementitious material (SCM). Bottom ash is generally underutilized due to its coarse particles, high porosity, and heterogeneous distribution, which results in non-uniform reactivity. To improve its usability, the ash was ground to two fineness levels (2,900 and 3,700 cm2/g) and used to replace ordinary Portland cement (OPC) at proportions ranging from 0 to 35 %. Its chemical and physical properties were analyzed using XRF, XRD, TG-DTG, and particle size measurement, and its effects on setting time, flowability, and compressive strength were evaluated. Increasing the replacement ratio delayed setting times and reduced early-age strength due to the dilution of reactive phases (C3S and C2S) and the presence of anhydrite (CaSO4). Flowability was not significantly influenced by fineness. Long-term strength improved, especially for the finer ash (3,700 cm2/g), which showed a narrower particle size distribution. The results suggest that CFB bottom ash with sufficient fineness can be used as an SCM in cement at replacement levels of up to 20 % without significantly compromising performance.

https://doi.org/10.4334/JKCI.2025.37.6.715

박건하(Geon-Ha Park) ; 오지섭(Ji-Seob Oh) ; 우진석(Jin-Seok Woo) ; 윤현도(Hyun-Do Yun) ; 김선우(Sun-Woo Kim) ; 박완신(Wan-Shin Park)

The flexural behavior of one-way concrete slabs reinforced with carbon fiber?reinforced polymer (CFRP) grids was investigated. To optimize the reinforcing effect of the CFRP grids, parameters such as strand width, thickness, and the number of grid layers were studied. Eight full-scale slab specimens?including six CFRP-reinforced and two RC slabs?were tested under a four-point bending setup. The experimental evaluation focused on crack development patterns, load?deflection and load?strain relationships, effective flexural stiffness, and flexural strength. The results indicated that slabs with lower reinforcement ratios, corresponding to minimum of 0.20 %, exhibited greater ultimate strain and more ductile failure behavior. In contrast, slabs with higher reinforcement ratios of 0.40 % demonstrated improved load capacity and enhanced mechanical performance relative to specimens reinforced with steel. Importantly, increasing CFRP strand width and the number of layers improved crack distribution and stress mitigation, whereas increasing CFRP strand thickness adversely affected bond performance, resulting in stress concentrations that ultimately degraded overall structural behavior. Furthermore, a comparison of flexural strength prediction models from ACI 440.11-22, KDS 14 20 68, and CSA S806-12 indicated that the selection of an appropriate model should be dependent on the reinforcement ratio, providing guidance for the optimized design of CFRP-reinforced slabs.

https://doi.org/10.4334/JKCI.2025.37.6.727

김용직(Yong Jic Kim)

In this study, the crack healing performance of mortar incorporating self-healing capsules was quantitatively evaluated using ultrasonic testing. These measurements were then used to determine the crack healing efficiency and to compare the healing performance of SHC with that of plain mortar. Additionally, the healing effects of SHC were indirectly verified through water flow tests. A significant positive correlation between crack depth reduction and healing rate was identified under both 600V and 1,200V pulse voltage conditions. Linear regression and analysis of variance (ANOVA) confirmed the statistical significance of the proposed model. Based on these results, ultrasonic testing could be a reliable method for quantitatively assessing the healing performance of self-healing mortar and has potential use in standardized assessment procedures.

https://doi.org/10.4334/JKCI.2025.37.6.737

이진용(Jin-Yong Lee) ; 이정배(Jeong-Bae Lee)

In the event of a tunnel fire, it is essential to ensure sufficient evacuation time and secure escape routes to protect users from structural damage or collapse. This study evaluated the thermal performance of an improved fire-resistant mortar developed to enhance thermal insulation and fire resistance, thereby minimizing damage to concrete structures during fire exposure. Fire simulation tests were conducted based on the Rijkswaterstaat (RWS) and modified hydrocarbon (HCM) curves for fire scenarios, using mortars incorporating vermiculite as a lightweight aggregate and ground granulated blast furnace slag and fly ash as binders. The evaluation included measurements of mortar density and thermal conductivity, residual compressive strength after heating, phase changes analyzed by XRD, temperature variation in mortar-coated concrete under fire simulation, and visual assessment of post-heating surface conditions. The results showed that mortars with SG (Ground-Granulated Blast-Furnace Slag) effectively suppressed heat transfer and enhanced resistance to melting. In addition, vermiculite contributed to reducing temperature rise when used in appropriate proportions, which was closely associated with improved thermal insulation. These findings provide foundational data for material design and performance optimization of fire-resistant mortars and are expected to inform future design strategies for the practical application of fire-resistant concrete structures.

https://doi.org/10.4334/JKCI.2025.37.6.747

정유진(Yu-Jin Jung) ; 이문석(Moon-Seok Lee) ; 손동희(Dong-Hee Son) ; 배백일(Beak-Il Bae) ; 최창식(Chang-Sik Choi)

This study analyzed the behavior and influence of lap splice length in precast concrete slabs incorporating 180-degree standard hooked bars. Complex failure patterns involving splitting failure, side cover spalling, and prying action were simultaneously observed. As the splice length increased, the stress level along the entire bar length generally increased, and, as with hooked bar development, stress transfer was predominantly governed by the straight and bent portions of the hooked bars. In addition, bar stress was transferred primarily through bond forces, while the contribution of bearing forces was relatively minor. When the KDS development length provisions were applied to lap splices using standard hooked bars without applying the modification factor, an equivalent or higher level of performance was achieved. However, when the modification factor was applied, the KDS development equations were found to overestimate the lap splice strength. Therefore, it is necessary to revise the current design provisions to ensure the required safety margin for development length when using hooked bars for lap splicing.

https://doi.org/10.4334/JKCI.2025.37.6.757

김우혁(Woo-Hyeok Kim) ; 양지수(Ji-Su Yang) ; 민근형(Geun-Hyeong Min) ; 신경준(Kyung Jun Shin) ; 김우석(WooSeok Kim)

This study was conducted to quantitatively evaluate the effects of chloride penetration and freeze-thaw action in deicing environments on the physical performance of concrete. Concrete specimens were soaked in four different solutions?deionized water (DIW), sodium chloride (), calcium chloride (), and a mixed deicing solution (D-ice)?for 30, 60, and 180 days, followed by an equal number of freeze-thaw cycles. Compressive strength, ultrasonic pulse velocity, and relative dynamic modulus were measured under each condition. Specimens soaked in DIW and retained approximately 93 % and over 86 % of their initial compressive strength after the final test, respectively. In contrast, specimens soaked in and D-ice showed significant strength reductions, retaining only about 32 % and 64 % of their original strength, respectively, after 180 days and freeze-thaw testing. Ultrasonic pulse velocity decreased to 75 % and 74 % for DIW and , and to 59 % and 49 % for and D-ice, respectively. The relative dynamic modulus decreased to 89 % and 96 % under DIW and conditions, while and D-ice showed reductions to 70 % and 73 %, respectively. These results demonstrate the combined deterioration effects of deicing salt composition and repeated freeze-thaw cycles on the durability of concrete bridge decks.

https://doi.org/10.4334/JKCI.2025.37.6.765

노병철(Byeong-Cheol Lho) ; 김영진(Young-Jin Kim)

This paper presents a comprehensive review of the performance characteristics of hardened concrete incorporating Portland-Limestone Cement (PLC), a more sustainable alternative to Ordinary Portland Cement (OPC). PLC enhances concrete performance through the synergistic physical and chemical actions of finely ground limestone. Physically, the limestone particles improve packing density (filler effect) and accelerate hydration by providing nucleation sites. Chemically, they react to form carboaluminate phases, which stabilize ettringite and refine the pore structure. With an optimized mix design, PLC concrete can achieve mechanical properties, particularly early-age strength, comparable or superior to those of OPC. However, limestone replacement levels exceeding 10~15 % may reduce long-term strength due to the dilution effect, a challenge that can be addressed by incorporating supplementary cementitious materials (SCMs). Regarding durability, PLC shows improved resistance to the alkali-silica reaction (ASR), while its performance under freeze-thaw, chloride and sulfate exposure depends on the limestone content and fineness. This review concludes that maximizing the potential of PLC requires advanced mix design and curing techniques, advocating for an integrated approach to its application in the construction industry.

https://doi.org/10.4334/JKCI.2025.37.6.777

이인용(Inyong Lee) ; 최종권(Jongkwon Choi)

This study quantitatively evaluated the effect of concrete moisture content, determined by different curing conditions, on mechanical properties in low-temperature environments. Concrete specimens cured under water, sealed, and air-dried conditions were tested under uniaxial compression at 20 °C, -20 °C , and -60 °C. Compressive strength, elastic modulus, strain at maximum stress, and representative moisture content were measured, and regression analyses were performed to assess temperature-property relationships. Compressive strength increased with decreasing temperature for all curing methods, with water curing showing the largest gain due to its high moisture content, which promotes densification of the microstructure during the water?ice phase transition. The rate of increase in elastic modulus also varied with curing method, with water curing exhibiting the steepest slope in linear regression, indicating greater stiffness improvement. These results show that concrete behavior in cold environments depends strongly on moisture content. Higher moisture content enhances strength, stiffness, and deformation capacity through microstructural densification. For cold-region structures, securing sufficient internal moisture via proper curing should be considered a key design parameter for long-term durability and safety.

https://doi.org/10.4334/JKCI.2025.37.6.787

이빛나(Binna Lee) ; 이종석(Jong Suk Lee)

The cement industry plays a critical role in achieving carbon neutrality by 2050, with clinker reduction and the use of supplementary cementitious materials (SCMs) recognized as effective strategies. While international standards have established regulations for multi-component cements based on the type and proportion of SCMs, fundamental data for establishing Korean KS standards are remain limited. In this study, four types of ternary blended concrete were prepared using ordinary Portland cement (Type I), fly ash, and blast furnace slag, with SCM replacement levels of 30 %, 40 %, and 50 % by mass of cement. The specimens were exposed in an outdoor exposure site for five years, and compressive strength, carbonation depth, and porosity were evaluated. The analysis showed that compressive strength decreased with increasing SCM replacement ratios. Although the strength difference diminished at long-term ages, it remained lower than that of the reference OPC specimen. Carbonation depth increased with higher SCM replacement ratios, but, the carbonation rate tended to slow from one year of age. Analysis of the five-year porosity indicated similar values across all specimens, regardless of the SCM content.

https://doi.org/10.4334/JKCI.2025.37.6.797

전세진(Se-Jin Jeon)

During the construction of prestressed concrete (PSC) structures, the management of tendon elongation during the tensioning of prestressing tendon is a critical factor to ensure that the PSC structure behaves as predicted in the design, including aspects such as camber and concrete stress distribution. For accurate elongation calculations, a variety of data must be considered without error, and in particular, the friction coefficients must be reasonably assumed. One of the key purposes of elongation management is to verify whether the assumed friction coefficients in the design are also valid in the field and to take corrective measures if necessary. However, in practice, there are frequent cases where the focus is limited to meeting the allowable elongation by arbitrarily adjusting friction coefficients, neglecting the validity of the calculations and the fundamental purpose of elongation management. This study discusses common errors and approximation-related discrepancies in elongation calculation during tensioning plans, and proposes improvement measures. Through example cases, it also aimed to comparatively examine the impact of such calculation errors and approximations.

https://doi.org/10.4334/JKCI.2025.37.6.807

신현섭(Hyun-Seop Shin) ; 김성욱(Sung-Wook Kim) ; 문재흠(Jae-Heum Moon) ; 김원우(Won-Woo Kim)

Although numerous studies have investigated non-ideal explosions, such as size effects, relatively few have mechanistically analyzed behaviors resulting from chemical reactions. In this study, parameters and their interrelationships related to non-ideal explosions were examined from a mechanical viewpoint using FE analysis with the ALE method. By analyzing the volumetric strain distribution within the explosive cylinder, it was possible to compare the expansion of the reaction products according to the cylinder diameter, allowing inferences regarding the corresponding pressure growth. Furthermore, by quantifying the confinement level using a physical parameter, it was possible to objectively analyze the effect of initial conditions, such as diameter size, on the pressure development. Finally, it was found that in order to examine whether the FE model used can adequately account for size effects, one possible approach is to analyze key parameters and their relationships, including detonation velocity, reaction rate, and detonation energy. Evaluation of explosive behavior is essential to more accurately predict the blast resistance of structures. Continued analysis of explosive behaviors under varying initial conditions is necessary to generalize these findings.

https://doi.org/10.4334/JKCI.2025.37.6.819

이정휘(Jungwhee Lee) ; 백인열(Inyeol Paik)

This paper presents a study to determine the impact factor applicable to the safety assessment of bridges subjected to heavy-vehicle loading. A measurement system was installed on a concrete hollow-slab bridge, and data obtained through loading tests and long-term monitoring were analyzed for a heavy low-bed trailer and a mobile-crane vehicle. Static displacements were determined by applying a low-pass filter to the dynamic displacement data from the loading tests and by referring to the low-speed loading results. The impact factors were then calculated and analyzed using dynamic displacement data for heavy vehicles extracted from the long-term monitoring records. For the slab bridge and heavy vehicles studied, the resulting impact factors were below the value defined in the current bridge code. The low-bed trailer exhibited a higher impact factor than the mobile crane due to the long distance between its middle axles and the amplified vibration generated at the rear axles.